Tube Hi-Fi directional AM antenna?


Rik
 

I have a circa 1959 Fisher Hi-Fi 101-R tuner which is so sensitive on FM it usually hears more than one station / freq here in the middle of Southern New England. I am at a high location with large cities in all directions, but no local transmitters. I have a Unidirectional FM antenna on its way.
AM is very sensitive too, and it has two selectivity settings, basically wide and wider still. An air core loop is often needed to separate AM stations on the same freq. I have the CCrane tuned/amplified ferrite and and a large ?Stormwise to try. I guess what I'd really like is something which can be used untuned to find stations on an unknown tuner frequency, which is more directional than the air core loops. High Q should help the wide and wider selectivity for DXing, but it might need to be tuned for that? Being able to switch in an antenna tuning cap would be ideal. An antenna with an amp would probably just overload the extremely sensitive Fisher tuner.

I am not able to make my own, so I am interested in something I can buy suitable for use with a tube tuner with screw terminals for AM, and likely to work better than what I have. - FARMERIK


Lee
 

Heh,heh....I have the Kenwood KT6040 AM/FM Tuner that has had the
filters replaced with lower value filters for tighter selectivity.
There is a 50KHz FM filter that gets in between "local" stations
and winkles out weaker stations hidden by "splatter" when in
"normal" (Hi Fi) 100KHz settings.... making it one "mean DX FM
machine"...

Regards.

Lee...G6ZSG.

--- In ultralightdx@..., "farmerik" <farmerik@...> wrote:

I have a circa 1959 Fisher Hi-Fi 101-R tuner which is so sensitive on FM it usually hears more than one station / freq here in the middle of Southern New England. I am at a high location with large cities in all directions, but no local transmitters. I have a Unidirectional FM antenna on its way.
AM is very sensitive too, and it has two selectivity settings, basically wide and wider still. An air core loop is often needed to separate AM stations on the same freq. I have the CCrane tuned/amplified ferrite and and a large ?Stormwise to try. I guess what I'd really like is something which can be used untuned to find stations on an unknown tuner frequency, which is more directional than the air core loops. High Q should help the wide and wider selectivity for DXing, but it might need to be tuned for that? Being able to switch in an antenna tuning cap would be ideal. An antenna with an amp would probably just overload the extremely sensitive Fisher tuner.

I am not able to make my own, so I am interested in something I can buy suitable for use with a tube tuner with screw terminals for AM, and likely to work better than what I have. - FARMERIK


Gabriel Velez
 

The problem isn't selectivity, which is separating adjacent stations (like 99.1 and 99.3) but receiving two stations on the same frequency.

The option in my mind for FM is to get the directional FM antenna and put in a potentiometer to control signal strength. I think one might be able to get some kind of user friendly one (meaning you don't have to make it yourself). These used to be readily available from your local electronics stores for television reception where a nearby strong adjacent station steps on the one one wishes to view.

http://www.kenselectronics.com/lists/tvant.htm

http://www.solidsignal.com/pview.asp?p=1296f&d=antennas-direct-20db-variable-attenuator-for-vhf-uhf-hd-off-air-reception-1296f&sku=853748001293

http://www.antennasdirect.com/store/variable_attenuator.html


For AM, the loop ought to be sufficient for directional selection. However, it won't help much if the stations are 180 degrees (one to the west and one to the east). However, with AM even if one has signal strength control, it is difficult to completely filter out the unwanted station on the same frequency without having to go into the electronics and add modifications. That tuner appears to have an IF sized AM RF antenna. I am not sure you can stick an external loop on that without adversely affecting the tuning.

So to summarize, use the directional FM antenna (hopefully you got a rotator also) with the attenuator (you might need to get baluns for either end of the wire and use coax all the way, which baluns will reduce signal strength a little also) to pick which station you want to listen to while reducing the other station to a point where the tuner can reject it.

For AM, the tuned passive loop (either air or ferrite) is your best bet.

Gabe

--- In ultralightdx@..., "Lee" <leo1949uk@...> wrote:



Heh,heh....I have the Kenwood KT6040 AM/FM Tuner that has had the
filters replaced with lower value filters for tighter selectivity.
There is a 50KHz FM filter that gets in between "local" stations
and winkles out weaker stations hidden by "splatter" when in
"normal" (Hi Fi) 100KHz settings.... making it one "mean DX FM
machine"...

Regards.

Lee...G6ZSG.



--- In ultralightdx@..., "farmerik" <farmerik@> wrote:

I have a circa 1959 Fisher Hi-Fi 101-R tuner which is so sensitive on FM it usually hears more than one station / freq here in the middle of Southern New England. I am at a high location with large cities in all directions, but no local transmitters. I have a Unidirectional FM antenna on its way.
AM is very sensitive too, and it has two selectivity settings, basically wide and wider still. An air core loop is often needed to separate AM stations on the same freq. I have the CCrane tuned/amplified ferrite and and a large ?Stormwise to try. I guess what I'd really like is something which can be used untuned to find stations on an unknown tuner frequency, which is more directional than the air core loops. High Q should help the wide and wider selectivity for DXing, but it might need to be tuned for that? Being able to switch in an antenna tuning cap would be ideal. An antenna with an amp would probably just overload the extremely sensitive Fisher tuner.

I am not able to make my own, so I am interested in something I can buy suitable for use with a tube tuner with screw terminals for AM, and likely to work better than what I have. - FARMERIK


Phillip Fimiani
 

Instead of buying a new antenna.... keep an eye on freecycle groups locally. I found a deep fringe antenna I want to use for meteor work tuning into long range FM sigs. You might find one free from whoever had the energy to take it off their roof. Maybe you can volunteer to take one down for a neighbor!

No I just have to find a free antenna rotor! lol
 
 
Best Regards
Phil
Lat: 40.8367633  Long: -74.1768412
 



From: gabevee
To: ultralightdx@...
Sent: Monday, June 3, 2013 12:01 PM
Subject: [ultralightdx] Re: Tube Hi-Fi directional AM antenna?

 
The problem isn't selectivity, which is separating adjacent stations (like 99.1 and 99.3) but receiving two stations on the same frequency.

The option in my mind for FM is to get the directional FM antenna and put in a potentiometer to control signal strength. I think one might be able to get some kind of user friendly one (meaning you don't have to make it yourself). These used to be readily available from your local electronics stores for television reception where a nearby strong adjacent station steps on the one one wishes to view.

http://www.kenselectronics.com/lists/tvant.htm

http://www.solidsignal.com/pview.asp?p=1296f&d=antennas-direct-20db-variable-attenuator-for-vhf-uhf-hd-off-air-reception-1296f&sku=853748001293

http://www.antennasdirect.com/store/variable_attenuator.html

For AM, the loop ought to be sufficient for directional selection. However, it won't help much if the stations are 180 degrees (one to the west and one to the east). However, with AM even if one has signal strength control, it is difficult to completely filter out the unwanted station on the same frequency without having to go into the electronics and add modifications. That tuner appears to have an IF sized AM RF antenna. I am not sure you can stick an external loop on that without adversely affecting the tuning.

So to summarize, use the directional FM antenna (hopefully you got a rotator also) with the attenuator (you might need to get baluns for either end of the wire and use coax all the way, which baluns will reduce signal strength a little also) to pick which station you want to listen to while reducing the other station to a point where the tuner can reject it.

For AM, the tuned passive loop (either air or ferrite) is your best bet.

Gabe

--- In ultralightdx@..., "Lee" wrote:
>
>
>
> Heh,heh....I have the Kenwood KT6040 AM/FM Tuner that has had the
> filters replaced with lower value filters for tighter selectivity.
> There is a 50KHz FM filter that gets in between "local" stations
> and winkles out weaker stations hidden by "splatter" when in
> "normal" (Hi Fi) 100KHz settings.... making it one "mean DX FM
> machine"...
>
> Regards.
>
> Lee...G6ZSG.
>
>
>
> --- In ultralightdx@..., "farmerik" wrote:
> >
> > I have a circa 1959 Fisher Hi-Fi 101-R tuner which is so sensitive on FM it usually hears more than one station / freq here in the middle of Southern New England. I am at a high location with large cities in all directions, but no local transmitters. I have a Unidirectional FM antenna on its way.
> > AM is very sensitive too, and it has two selectivity settings, basically wide and wider still. An air core loop is often needed to separate AM stations on the same freq. I have the CCrane tuned/amplified ferrite and and a large ?Stormwise to try. I guess what I'd really like is something which can be used untuned to find stations on an unknown tuner frequency, which is more directional than the air core loops. High Q should help the wide and wider selectivity for DXing, but it might need to be tuned for that? Being able to switch in an antenna tuning cap would be ideal. An antenna with an amp would probably just overload the extremely sensitive Fisher tuner.
> >
> > I am not able to make my own, so I am interested in something I can buy suitable for use with a tube tuner with screw terminals for AM, and likely to work better than what I have. - FARMERIK
> >
>




Lee
 

If you`re receiving two FM stations on the same frequency then it IS
selectivity... you need attenuation... try soldering a resistor in
line with the centre core of the antenna coax - try 1kilohm to
2megohm! or a 2meg potentiometer (not advisable) if using twinfeed
then a resistor on both lines, keeping the feed balance correct.

Then you might winkle some DX from the gaps.

In europe, there are stations EVERY 100khz..very full..so a selective
receiver is paramount.

Regards.

Lee...G6ZSG,

--- In ultralightdx@..., "gabevee" <gabevee@...> wrote:

The problem isn't selectivity, which is separating adjacent stations (like 99.1 and 99.3) but receiving two stations on the same frequency.

The option in my mind for FM is to get the directional FM antenna and put in a potentiometer to control signal strength. I think one might be able to get some kind of user friendly one (meaning you don't have to make it yourself). These used to be readily available from your local electronics stores for television reception where a nearby strong adjacent station steps on the one one wishes to view.

http://www.kenselectronics.com/lists/tvant.htm

http://www.solidsignal.com/pview.asp?p=1296f&d=antennas-direct-20db-variable-attenuator-for-vhf-uhf-hd-off-air-reception-1296f&sku=853748001293

http://www.antennasdirect.com/store/variable_attenuator.html


For AM, the loop ought to be sufficient for directional selection. However, it won't help much if the stations are 180 degrees (one to the west and one to the east). However, with AM even if one has signal strength control, it is difficult to completely filter out the unwanted station on the same frequency without having to go into the electronics and add modifications. That tuner appears to have an IF sized AM RF antenna. I am not sure you can stick an external loop on that without adversely affecting the tuning.

So to summarize, use the directional FM antenna (hopefully you got a rotator also) with the attenuator (you might need to get baluns for either end of the wire and use coax all the way, which baluns will reduce signal strength a little also) to pick which station you want to listen to while reducing the other station to a point where the tuner can reject it.

For AM, the tuned passive loop (either air or ferrite) is your best bet.

Gabe



--- In ultralightdx@..., "Lee" <leo1949uk@> wrote:



Heh,heh....I have the Kenwood KT6040 AM/FM Tuner that has had the
filters replaced with lower value filters for tighter selectivity.
There is a 50KHz FM filter that gets in between "local" stations
and winkles out weaker stations hidden by "splatter" when in
"normal" (Hi Fi) 100KHz settings.... making it one "mean DX FM
machine"...

Regards.

Lee...G6ZSG.



--- In ultralightdx@..., "farmerik" <farmerik@> wrote:

I have a circa 1959 Fisher Hi-Fi 101-R tuner which is so sensitive on FM it usually hears more than one station / freq here in the middle of Southern New England. I am at a high location with large cities in all directions, but no local transmitters. I have a Unidirectional FM antenna on its way.
AM is very sensitive too, and it has two selectivity settings, basically wide and wider still. An air core loop is often needed to separate AM stations on the same freq. I have the CCrane tuned/amplified ferrite and and a large ?Stormwise to try. I guess what I'd really like is something which can be used untuned to find stations on an unknown tuner frequency, which is more directional than the air core loops. High Q should help the wide and wider selectivity for DXing, but it might need to be tuned for that? Being able to switch in an antenna tuning cap would be ideal. An antenna with an amp would probably just overload the extremely sensitive Fisher tuner.

I am not able to make my own, so I am interested in something I can buy suitable for use with a tube tuner with screw terminals for AM, and likely to work better than what I have. - FARMERIK


Michael <michael.setaazul@...>
 

--- In ultralightdx@..., "gabevee" <gabevee@...> wrote:

The problem isn't selectivity, which is separating adjacent stations
(like 99.1 and 99.3) but receiving two stations on the same frequency.
Gabe
---------------------------------

If the two FM signals are on the same frequency but approx 180 apart,
I would try a dipole in front of a mesh reflector. The attenuation of the
unwanted signal should be sufficient for the wanted one to prevail.
An up-scaled version of a UHF design should be feasible, for
example.

Michael

Not quite sure how a tube hi-fi receiver would squeeze into
uldx size limitations, even though there appear to be none
for the antenna configuration :-) Long live creativity!


Michael <michael.setaazul@...>
 

Not quite sure how a tube hi-fi receiver would squeeze into
uldx size limitations; however, there appears to be none
for the antenna configuration :-) Long live creativity!

If the two FM signals are on the same frequency but approx 180 apart,
I would try a dipole in front of a mesh reflector. The attenuation of the
unwanted signal should be sufficient for the wanted one to prevail.
An down-scaled version of a UHF design should be feasible, for
example.

Michael

--- In ultralightdx@..., "gabevee" wrote:

The problem isn't selectivity, which is separating adjacent stations
(like 99.1 and 99.3) but receiving two stations on the same frequency.
Gabe


Gabriel Velez
 

No, you are incorrect. Selectivity pertains to adjacent stations and interference of other frequencies.

"Selectivity is a measure of the performance of a radio receiver to respond only to the radio signal it is tuned to (such as a radio station) and reject other signals nearby in frequency, such as another broadcast on an adjacent channel." - http://en.wikipedia.org/wiki/Selectivity_%28electronic%29

"Selectivity of any radio receiver is described as the ability to only receive the radio stations that the radio is tuned into while rejecting all other frequencies which can be the adjacent channel station, man made other unwanted frequencies. Rejecting unwanted frequencies will give you a good indication of the radios quality usually specified as adjacent channel rejection ratio." - http://www.kc2ra.org/index.php/jacks-corner/163-two-main-qualities-of-a-radio-receiver

Wide bandwidth results in lower selectivity. A narrow bandwidth, or better yet one that is sharper, that is has a sharper roll off at the specified parameters, (10 kilohertz, in the case of AM) makes the receiver more selective.

The fact that one signal of the same frequency steps on another does not mean the radio has poor selectivity. And the only thing that can be done about that in the case of FM is to use a very directional antenna, not a dipole, but a multipole (well, those are actually dipoles with various sized directors and reflectors. The mesh isn't enough) and some attenuator which will reduce the secondary signal from behind or whatever direction, which will be weaker than the signal directly in front of the antenna, so as to only allow the stronger of the two to be received.

Also, kilohm to megohm resistances are absurd for FM, as the impedance for the FM antenna is 300 ohms! Even for AM megohm values are absurd.

No, my suggestion of using the baluns to match the receiver's 300 ohm FM to the 75 ohm coax to use the attenuator I suggest is the correct one, considering the user said he didn't want to make one.

Gabe

--- In ultralightdx@..., "Lee" <leo1949uk@...> wrote:

If you`re receiving two FM stations on the same frequency then it IS
selectivity... you need attenuation... try soldering a resistor in
line with the centre core of the antenna coax - try 1kilohm to
2megohm! or a 2meg potentiometer (not advisable) if using twinfeed
then a resistor on both lines, keeping the feed balance correct.

Then you might winkle some DX from the gaps.

In europe, there are stations EVERY 100khz..very full..so a selective
receiver is paramount.

Regards.

Lee...G6ZSG,



--- In ultralightdx@..., "gabevee" <gabevee@> wrote:

The problem isn't selectivity, which is separating adjacent stations (like 99.1 and 99.3) but receiving two stations on the same frequency.

The option in my mind for FM is to get the directional FM antenna and put in a potentiometer to control signal strength. I think one might be able to get some kind of user friendly one (meaning you don't have to make it yourself). These used to be readily available from your local electronics stores for television reception where a nearby strong adjacent station steps on the one one wishes to view.

http://www.kenselectronics.com/lists/tvant.htm

http://www.solidsignal.com/pview.asp?p=1296f&d=antennas-direct-20db-variable-attenuator-for-vhf-uhf-hd-off-air-reception-1296f&sku=853748001293

http://www.antennasdirect.com/store/variable_attenuator.html


For AM, the loop ought to be sufficient for directional selection. However, it won't help much if the stations are 180 degrees (one to the west and one to the east). However, with AM even if one has signal strength control, it is difficult to completely filter out the unwanted station on the same frequency without having to go into the electronics and add modifications. That tuner appears to have an IF sized AM RF antenna. I am not sure you can stick an external loop on that without adversely affecting the tuning.

So to summarize, use the directional FM antenna (hopefully you got a rotator also) with the attenuator (you might need to get baluns for either end of the wire and use coax all the way, which baluns will reduce signal strength a little also) to pick which station you want to listen to while reducing the other station to a point where the tuner can reject it.

For AM, the tuned passive loop (either air or ferrite) is your best bet.

Gabe



--- In ultralightdx@..., "Lee" <leo1949uk@> wrote:



Heh,heh....I have the Kenwood KT6040 AM/FM Tuner that has had the
filters replaced with lower value filters for tighter selectivity.
There is a 50KHz FM filter that gets in between "local" stations
and winkles out weaker stations hidden by "splatter" when in
"normal" (Hi Fi) 100KHz settings.... making it one "mean DX FM
machine"...

Regards.

Lee...G6ZSG.



--- In ultralightdx@..., "farmerik" <farmerik@> wrote:

I have a circa 1959 Fisher Hi-Fi 101-R tuner which is so sensitive on FM it usually hears more than one station / freq here in the middle of Southern New England. I am at a high location with large cities in all directions, but no local transmitters. I have a Unidirectional FM antenna on its way.
AM is very sensitive too, and it has two selectivity settings, basically wide and wider still. An air core loop is often needed to separate AM stations on the same freq. I have the CCrane tuned/amplified ferrite and and a large ?Stormwise to try. I guess what I'd really like is something which can be used untuned to find stations on an unknown tuner frequency, which is more directional than the air core loops. High Q should help the wide and wider selectivity for DXing, but it might need to be tuned for that? Being able to switch in an antenna tuning cap would be ideal. An antenna with an amp would probably just overload the extremely sensitive Fisher tuner.

I am not able to make my own, so I am interested in something I can buy suitable for use with a tube tuner with screw terminals for AM, and likely to work better than what I have. - FARMERIK


Lee
 

--- In ultralightdx@..., "gabevee" <gabevee@...> wrote:

No, you are incorrect. Selectivity pertains to adjacent stations and interference of other frequencies.
have you read my original post??

"Selectivity is a measure of the performance of a radio receiver to respond only to the radio signal it is tuned to (such as a radio station) and reject other signals nearby in frequency, such as another broadcast on an adjacent channel." - http://en.wikipedia.org/wiki/Selectivity_%28electronic%29

"Selectivity of any radio receiver is described as the ability to only receive the radio stations that the radio is tuned into while rejecting all other frequencies which can be the adjacent channel station, man made other unwanted frequencies. Rejecting unwanted frequencies will give you a good indication of the radios quality usually specified as adjacent channel rejection ratio." - http://www.kc2ra.org/index.php/jacks-corner/163-two-main-qualities-of-a-radio-receiver

Wide bandwidth results in lower selectivity. A narrow bandwidth, or better yet one that is sharper, that is has a sharper roll off at the specified parameters, (10 kilohertz, in the case of AM) makes the receiver more selective.

The fact that one signal of the same frequency steps on another does not mean the radio has poor selectivity. And the only thing that can be done about that in the case of FM is to use a very directional antenna, not a dipole, but a multipole (well, those are actually dipoles with various sized directors and reflectors. The mesh isn't enough) and some attenuator which will reduce the secondary signal from behind or whatever direction, which will be weaker than the signal directly in front of the antenna, so as to only allow the stronger of the two to be received.

Also, kilohm to megohm resistances are absurd for FM, as the impedance for the FM antenna is 300 ohms! Even for AM megohm values are absurd.
I have some belling-lee coaxial attenuators that plug into the t/v
socket and the coax plugs into the attenuator.. the smallest being
1 kilohm... the highest attenuator being 1 megohm .. the antenna
coax is 75 ohm !!!! Antiference is the manufacturer !!!


No, my suggestion of using the baluns to match the receiver's 300 ohm FM to the 75 ohm coax to use the attenuator I suggest is the correct one, considering the user said he didn't want to make one.
European equipment generally 75 ohm ccoaxial cable the antenna
already has a balun fitted... different to 300 ohm balanced in the
usa...

Gabe
Regards.


Lee...G6ZSG.


--- In ultralightdx@..., "Lee" <leo1949uk@> wrote:

If you`re receiving two FM stations on the same frequency then it IS
selectivity... you need attenuation... try soldering a resistor in
line with the centre core of the antenna coax - try 1kilohm to
2megohm! or a 2meg potentiometer (not advisable) if using twinfeed
then a resistor on both lines, keeping the feed balance correct.

Then you might winkle some DX from the gaps.

In europe, there are stations EVERY 100khz..very full..so a selective
receiver is paramount.

Regards.

Lee...G6ZSG,


Gabriel Velez
 

--- In ultralightdx@..., "Lee" <leo1949uk@...> wrote:

[snip]

Also, kilohm to megohm resistances are absurd for FM, as the impedance for the FM antenna is 300 ohms! Even for AM megohm values are absurd.
I have some belling-lee coaxial attenuators that plug into the t/v
socket and the coax plugs into the attenuator.. the smallest being
1 kilohm... the highest attenuator being 1 megohm .. the antenna
coax is 75 ohm !!!! Antiference is the manufacturer !!!


No, my suggestion of using the baluns to match the receiver's 300 ohm FM to the 75 ohm coax to use the attenuator I suggest is the correct one, considering the user said he didn't want to make one.
European equipment generally 75 ohm ccoaxial cable the antenna
already has a balun fitted... different to 300 ohm balanced in the
usa...
USA equipment has both., I repeat, those values are absurd for attenuators. I suspect you are seeing the frequency range as resistance values. The numbers you specify are impossible for 2-15 dB attenuation. They are likely 5 kilohertz to 1000 megahertz.

Attenuation for RF like AC is virtually the same as for DC. 1 kilohertz in line with 75 ohms makes the signal virtually zero. And we're talking about microvolt levels.

Specs from ANTIFERENCE:

http://www.vanjak.com/index.php?dispatch=products.view&product_id=33261

The internal circuit is made of resistors as you seem to know. However the 75 ohm impedance must be matched. That means the input and output resistor must be 75 ohms. The resistor from the input to the output, to drop 6 decibels, which his half the voltage, must be 75 ohms! It is a simple voltage divider circuit.

Z2/Z1+Z2 X Vin

The input 75 ohms doesn't count unless you worry about the current, which is in the pico range. Inputs to RF in receivers are generally only concerned about voltage. So the input resist provides a fixed load for the signal to prevent standing waves. So we have 75 ohms plus 75 ohms for 150 ohms. 75 ohms over 150 ohms times the input voltage is the same as 1/2 the input voltage. 6dB drop. Voltage. The dB level is different for power (femtowatt).

1 kilo to 1 megohm is *ABSURD*.

Gabe


Gary Kinsman
 

Lee,

Picking up two stations on the same frequency on FM is a function of the capture ratio, not selectivity. The lower the capture ratio, the better an FM tuner will be able to separate two FM signals on the same frequency. The signals have to be different in strength by at least the capture ratio (which is measured in dB) in order to do this. As Gabe pointed out, selectivity pertains to separating stations on adjacent frequencies, not the same frequency. Since it's probably not easy or practical to modify an FM tuner to improve the capture ratio, a directional antenna, possibly combined with variable attenuation, may be one solution.

-Gary

--- In ultralightdx@..., "Lee" <leo1949uk@...> wrote:

If you`re receiving two FM stations on the same frequency then it IS
selectivity... you need attenuation... try soldering a resistor in
line with the centre core of the antenna coax - try 1kilohm to
2megohm! or a 2meg potentiometer (not advisable) if using twinfeed
then a resistor on both lines, keeping the feed balance correct.

Then you might winkle some DX from the gaps.

In europe, there are stations EVERY 100khz..very full..so a selective
receiver is paramount.

Regards.

Lee...G6ZSG,


Lee
 

Nevertheless... they WORK, to quickly analyze a front end like a
barn door that`s trying to de-mod a crashing signal!

Have you checked what is inside a coaxial attenuator ?

Don`t scoff without testing.. not everyone has a service bay in
their basement and university pass in radio.. they have to use
what`s to hand... :) lol.

Regards,

Lee...G6ZSG.

--- In ultralightdx@..., "gabevee" <gabevee@...> wrote:



--- In ultralightdx@..., "Lee" <leo1949uk@> wrote:

[snip]

Also, kilohm to megohm resistances are absurd for FM, as the impedance for the FM antenna is 300 ohms! Even for AM megohm values are absurd.
I have some belling-lee coaxial attenuators that plug into the t/v
socket and the coax plugs into the attenuator.. the smallest being
1 kilohm... the highest attenuator being 1 megohm .. the antenna
coax is 75 ohm !!!! Antiference is the manufacturer !!!


No, my suggestion of using the baluns to match the receiver's 300 ohm FM to the 75 ohm coax to use the attenuator I suggest is the correct one, considering the user said he didn't want to make one.
European equipment generally 75 ohm ccoaxial cable the antenna
already has a balun fitted... different to 300 ohm balanced in the
usa...
USA equipment has both., I repeat, those values are absurd for attenuators. I suspect you are seeing the frequency range as resistance values. The numbers you specify are impossible for 2-15 dB attenuation. They are likely 5 kilohertz to 1000 megahertz.

Attenuation for RF like AC is virtually the same as for DC. 1 kilohertz in line with 75 ohms makes the signal virtually zero. And we're talking about microvolt levels.

Specs from ANTIFERENCE:

http://www.vanjak.com/index.php?dispatch=products.view&product_id=33261

The internal circuit is made of resistors as you seem to know. However the 75 ohm impedance must be matched. That means the input and output resistor must be 75 ohms. The resistor from the input to the output, to drop 6 decibels, which his half the voltage, must be 75 ohms! It is a simple voltage divider circuit.

Z2/Z1+Z2 X Vin

The input 75 ohms doesn't count unless you worry about the current, which is in the pico range. Inputs to RF in receivers are generally only concerned about voltage. So the input resist provides a fixed load for the signal to prevent standing waves. So we have 75 ohms plus 75 ohms for 150 ohms. 75 ohms over 150 ohms times the input voltage is the same as 1/2 the input voltage. 6dB drop. Voltage. The dB level is different for power (femtowatt).

1 kilo to 1 megohm is *ABSURD*.

Gabe


Lee
 

Gary... I agree with what you say, except, Farmerick did not say the
stations were on the same frequency (on FM) he said "stations /f"
whatever that "f" means in context, if not a typo!!

Regards.

Lee...G6ZSG.

--- In ultralightdx@..., "gkinsman1" <gkinsman@...> wrote:



Lee,

Picking up two stations on the same frequency on FM is a function of the capture ratio, not selectivity. The lower the capture ratio, the better an FM tuner will be able to separate two FM signals on the same frequency. The signals have to be different in strength by at least the capture ratio (which is measured in dB) in order to do this. As Gabe pointed out, selectivity pertains to separating stations on adjacent frequencies, not the same frequency. Since it's probably not easy or practical to modify an FM tuner to improve the capture ratio, a directional antenna, possibly combined with variable attenuation, may be one solution.

-Gary

--- In ultralightdx@..., "Lee" <leo1949uk@> wrote:

If you`re receiving two FM stations on the same frequency then it IS
selectivity... you need attenuation... try soldering a resistor in
line with the centre core of the antenna coax - try 1kilohm to
2megohm! or a 2meg potentiometer (not advisable) if using twinfeed
then a resistor on both lines, keeping the feed balance correct.

Then you might winkle some DX from the gaps.

In europe, there are stations EVERY 100khz..very full..so a selective
receiver is paramount.

Regards.

Lee...G6ZSG,


Gabriel Velez
 

Replies below.

--- In ultralightdx@..., "Lee" <leo1949uk@...> wrote:

Nevertheless... they WORK, to quickly analyze a front end like a
barn door that`s trying to de-mod a crashing signal!

Have you checked what is inside a coaxial attenuator ?
Evidently, you haven't. Yes, since I have been playing with electronics from 9 years old (41 years ago) I have broken apart my share of gadgets, including attenuators. Resistors valued at the rated impedance, from several ohms to a few hundred.

I have been an electronics engineer for 28 of those years, BTW.

Don`t scoff without testing.. not everyone has a service bay in
their basement and university pass in radio.. they have to use
what`s to hand... :) lol.

Regards,
You have obviously ignored the links I provided as actual technical reference.

No, not everyone has a basement lab or university pass (degree, I presume), which is why they ought to pay attention and listen to those of us who DO. ;-)

Don't scoff without *knowing*. What's at hand does *not* use thousands to millions of ohms. That's absurd.

Here is another reference:

http://www.radio-electronics.com/info/rf-technology-design/attenuators/attenuator-resistor-values.php

Nothing over 500 ohms. This is for a 50 ohm however. 75 ohm would not be much more.

Gabe


Gabriel Velez
 

Wow... someone needs to look a little closer.

The actual quote is:
"...which is so sensitive on FM it usually hears more than one station / freq here in the middle of Southern New England."

That is, he hears multiple stations PER FREQUENCY. IN CONTEXT. Not a typo.

Even you acknowledged that when you replied to me incorrectly stating that two stations on the same frequency meant a selectivity problem.

Or would Britons have said what Farmerick meant differently?

Gabe

--- In ultralightdx@..., "Lee" <leo1949uk@...> wrote:

Gary... I agree with what you say, except, Farmerick did not say the
stations were on the same frequency (on FM) he said "stations /f"
whatever that "f" means in context, if not a typo!!

Regards.

Lee...G6ZSG.


--- In ultralightdx@..., "gkinsman1" <gkinsman@> wrote:



Lee,

Picking up two stations on the same frequency on FM is a function of the capture ratio, not selectivity. The lower the capture ratio, the better an FM tuner will be able to separate two FM signals on the same frequency. The signals have to be different in strength by at least the capture ratio (which is measured in dB) in order to do this. As Gabe pointed out, selectivity pertains to separating stations on adjacent frequencies, not the same frequency. Since it's probably not easy or practical to modify an FM tuner to improve the capture ratio, a directional antenna, possibly combined with variable attenuation, may be one solution.

-Gary

--- In ultralightdx@..., "Lee" <leo1949uk@> wrote:

If you`re receiving two FM stations on the same frequency then it IS
selectivity... you need attenuation... try soldering a resistor in
line with the centre core of the antenna coax - try 1kilohm to
2megohm! or a 2meg potentiometer (not advisable) if using twinfeed
then a resistor on both lines, keeping the feed balance correct.

Then you might winkle some DX from the gaps.

In europe, there are stations EVERY 100khz..very full..so a selective
receiver is paramount.

Regards.

Lee...G6ZSG,


Lee
 

lol

--- In ultralightdx@..., "gabevee" <gabevee@...> wrote:

Replies below.

--- In ultralightdx@..., "Lee" <leo1949uk@> wrote:

Nevertheless... they WORK, to quickly analyze a front end like a
barn door that`s trying to de-mod a crashing signal!

Have you checked what is inside a coaxial attenuator ?
Evidently, you haven't. Yes, since I have been playing with electronics from 9 years old (41 years ago) I have broken apart my share of gadgets, including attenuators. Resistors valued at the rated impedance, from several ohms to a few hundred.

I have been an electronics engineer for 28 of those years, BTW.

Don`t scoff without testing.. not everyone has a service bay in
their basement and university pass in radio.. they have to use
what`s to hand... :) lol.

Regards,
You have obviously ignored the links I provided as actual technical reference.

No, not everyone has a basement lab or university pass (degree, I presume), which is why they ought to pay attention and listen to those of us who DO. ;-)

Don't scoff without *knowing*. What's at hand does *not* use thousands to millions of ohms. That's absurd.

Here is another reference:

http://www.radio-electronics.com/info/rf-technology-design/attenuators/attenuator-resistor-values.php

Nothing over 500 ohms. This is for a 50 ohm however. 75 ohm would not be much more.

Gabe


Lee
 

--- In ultralightdx@..., "gabevee" <gabevee@...> wrote:

Wow... someone needs to look a little closer.

The actual quote is:
"...which is so sensitive on FM it usually hears more than one station / freq here in the middle of Southern New England."

That is, he hears multiple stations PER FREQUENCY. IN CONTEXT. Not a typo.
Heh heh.

Thankyou... most people don`t short cut using /f.. "PER FREQUENCY"
is far clearer... it tells me it IS A BARN DOOR front end, I have
a homebrew FM Superegen that sounds like that when I wind the wick
up.. lol..

Yes, I have an attenuator dismantled in front of me...

Enough already...send me an e-mail if you wish to
continue the flames ... I was 9 in 1949 :)

Regards.

Lee...G6ZSG.









Even you acknowledged that when you replied to me incorrectly stating that two stations on the same frequency meant a selectivity problem.

Or would Britons have said what Farmerick meant differently?

Gabe

--- In ultralightdx@..., "Lee" <leo1949uk@> wrote:

Gary... I agree with what you say, except, Farmerick did not say the
stations were on the same frequency (on FM) he said "stations /f"
whatever that "f" means in context, if not a typo!!

Regards.

Lee...G6ZSG.


--- In ultralightdx@..., "gkinsman1" <gkinsman@> wrote:



Lee,

Picking up two stations on the same frequency on FM is a function of the capture ratio, not selectivity. The lower the capture ratio, the better an FM tuner will be able to separate two FM signals on the same frequency. The signals have to be different in strength by at least the capture ratio (which is measured in dB) in order to do this. As Gabe pointed out, selectivity pertains to separating stations on adjacent frequencies, not the same frequency. Since it's probably not easy or practical to modify an FM tuner to improve the capture ratio, a directional antenna, possibly combined with variable attenuation, may be one solution.

-Gary

--- In ultralightdx@..., "Lee" <leo1949uk@> wrote:

If you`re receiving two FM stations on the same frequency then it IS
selectivity... you need attenuation... try soldering a resistor in
line with the centre core of the antenna coax - try 1kilohm to
2megohm! or a 2meg potentiometer (not advisable) if using twinfeed
then a resistor on both lines, keeping the feed balance correct.

Then you might winkle some DX from the gaps.

In europe, there are stations EVERY 100khz..very full..so a selective
receiver is paramount.

Regards.

Lee...G6ZSG,


Gabriel Velez
 

--- In ultralightdx@..., "Lee" <leo1949uk@...> wrote:



--- In ultralightdx@..., "gabevee" <gabevee@> wrote:

Wow... someone needs to look a little closer.

The actual quote is:
"...which is so sensitive on FM it usually hears more than one station / freq here in the middle of Southern New England."

That is, he hears multiple stations PER FREQUENCY. IN CONTEXT. Not a typo.
Heh heh.

Thankyou... most people don`t short cut using /f..
No, not /f, but / freq.

"PER FREQUENCY"
is far clearer... it tells me it IS A BARN DOOR front end, I have
a homebrew FM Superegen that sounds like that when I wind the wick
up.. lol..

Yes, I have an attenuator dismantled in front of me...

Enough already...send me an e-mail if you wish to
continue the flames ... I was 9 in 1949 :)
Then you should know better. Not going to personalize this via email. Nor am I trying to flame anyone. There's enough evidence to show the correct technology.

Question: what do you mean by "barn door"? That it's "wide enough" to let anything in? If you've looked at the schematic the front end is as it has always been since Armstrong invented FM. A high Q RF tuner, second Rf stage, local oscillator, IF stages.

Superregen won't separate two equidistant FM stations from being received at the same time at the same frequency. And oddly enough, your statement about "turning up the wick" reinforces what I said about using an adjustable attenuator in the line of the antenna. The reason your regen does that is because now you've increased the sensitivity.

And now we seem to have come full circle.

Gabe


Rik
 

I did receive the directional FM antenna ordered from Universal Radio, and tried it on my PL-390 because it has ETM.

On the fully extended whip, ETM locked onto 32 stations here about 5:20 PM local time and using the directional antenna I got 59. I turned the antenna about 90 degrees and got 57.

I wasn't sure if the PL-390 would like the 300 Ohm antenna connected without a matching transformer to the 1/8 th inch mini telephone plug, but it does seem to work well. Does anyone think a matching transformer to 50 or 75 Ohms would be significantly better?

The directional antenna is just near the ceiling in my radio room, only a couple feet higher than the top of the whip, not outside on a mast.

In switching from the 4 foot LW loop and putting the FM antenna in that spot, I damaged the end winding. I had been considering removing turns and using it for AM BCB. If I left some turns and grounded them at one end, does any one think it would shield AM signals from that side enough to help? [when an other station on the frequency is in the opposite direction?]

The reason I ask so many questions as I do is because I am disabled, and just trying things can take a lot of time and effort, so I'd like to only try things which people with more understanding of radio theory think could work.

-FARMERIK

--- In ultralightdx@..., "Lee" <leo1949uk@...> wrote:

Gary... I agree with what you say, except, Farmerick did not say the
stations were on the same frequency (on FM) he said "stations /f"
whatever that "f" means in context, if not a typo!!

Regards.

Lee...G6ZSG.


--- In ultralightdx@..., "gkinsman1" <gkinsman@> wrote:



Lee,

Picking up two stations on the same frequency on FM is a function of the capture ratio, not selectivity. The lower the capture ratio, the better an FM tuner will be able to separate two FM signals on the same frequency. The signals have to be different in strength by at least the capture ratio (which is measured in dB) in order to do this. As Gabe pointed out, selectivity pertains to separating stations on adjacent frequencies, not the same frequency. Since it's probably not easy or practical to modify an FM tuner to improve the capture ratio, a directional antenna, possibly combined with variable attenuation, may be one solution.

-Gary

--- In ultralightdx@..., "Lee" <leo1949uk@> wrote:

If you`re receiving two FM stations on the same frequency then it IS
selectivity... you need attenuation... try soldering a resistor in
line with the centre core of the antenna coax - try 1kilohm to
2megohm! or a 2meg potentiometer (not advisable) if using twinfeed
then a resistor on both lines, keeping the feed balance correct.

Then you might winkle some DX from the gaps.

In europe, there are stations EVERY 100khz..very full..so a selective
receiver is paramount.

Regards.

Lee...G6ZSG,


Gabriel Velez
 

I say if it works as it is, and provides you with the stations without them stepping on each other, then simply use it as is.

I think the matching transformer would be better for the PL-390, but you would not need it for the Fisher. But use 75 ohm. 50 ohm is generally used for transmitters and two-way HAM gear.

For AM, it is virtually impossible (it is possible, but needs a big back yard) to make 180 degrees directional (but it *is* 90 degree directional, unless one uses a long wire antenna and small non directional coil) for a couple of reasons. One is the wavelength. The wavelength for FM is, using 100 MHz, 3 meters (one an use 1/4 wavelength to make a very effective antenna, which makes it 2.5 feet). AM at 1 MHz is 300 meters. The other is AM is more ubiquitous. One can get a signal from both the ground and the air. That's some of why AM can be received from a much further distance. In fact, I was reading an article from the 1970s speaking of how using trees as antennas worked well for low frequencies.

Even attenuating AM one still gets weaker stations bleeding in.

Of course, one can play with AM traps but it is more suited to reducing the strength of adjacent frequency stations which overpower weaker stations. But not on the same frequency.

Gabe

--- In ultralightdx@..., "farmerik" <farmerik@...> wrote:

I did receive the directional FM antenna ordered from Universal Radio, and tried it on my PL-390 because it has ETM.

On the fully extended whip, ETM locked onto 32 stations here about 5:20 PM local time and using the directional antenna I got 59. I turned the antenna about 90 degrees and got 57.

I wasn't sure if the PL-390 would like the 300 Ohm antenna connected without a matching transformer to the 1/8 th inch mini telephone plug, but it does seem to work well. Does anyone think a matching transformer to 50 or 75 Ohms would be significantly better?

The directional antenna is just near the ceiling in my radio room, only a couple feet higher than the top of the whip, not outside on a mast.

In switching from the 4 foot LW loop and putting the FM antenna in that spot, I damaged the end winding. I had been considering removing turns and using it for AM BCB. If I left some turns and grounded them at one end, does any one think it would shield AM signals from that side enough to help? [when an other station on the frequency is in the opposite direction?]

The reason I ask so many questions as I do is because I am disabled, and just trying things can take a lot of time and effort, so I'd like to only try things which people with more understanding of radio theory think could work.

-FARMERIK