Filter width on DSP radios


Gary Kinsman
 

Hello all,

I noticed that on my PL-380, I can detune up to one filter width and still get good sound quality. For example, if I'm listening to 1070 kHz with the 2 kHz filter, I can tune as low as 1068 kHz or as high as 1072 kHz.

In the past, I've always used the rule that you can detune up to one half the filter width. This is how is works with my Satellit 800 and Icom R75 for example. With the 4 kHz filter selected on the Sat 800, I can detune by 2 kHz.

This leads me to believe that on the Tecsun DSP radios, the specified filter width is half as wide as it is on my other radios. For example, the 2 kHz DSP filter is equivalent to a 4 kHz filter on my other radios.

On most of my radios the filter width is specified using both sidebands; on the DSP radio it appears to be specified using just one sideband. I always thought the former was the standard way of measuring filters. Is this not the case?

Regards,
Gary


Kevin Schanilec
 

Hi Gary:

You've got it spot-on: the DSP bandwidth is specified per sideband, not for the whole thing like most filters. So, the 1 khz bandwidth is actually a 2 khz (total) in normal parlance.

At the beach last time listening to split frequency targets, I did some comparisons between DSP filtering and the outstanding 2.4 khz Murata filter that has found its way into a lot of Eton e100's and CCrane SWP's. The Murata is tighter than the 1 khz (2 khz total) filter on the DSP radios, so kudos to Murata for still having the best filtering. For instance, listening to 738 under a domestic on 740, the Murata has less slop when the receiver is detuned by a khz to 737. So, the 1 khz DSP setting might be better compared to a 2.8 khz "regular" filter - still pretty darn good.

Since the 1 khz DSP filter does allow a little more signal through, one can detune by 2 khz (i.e., down to 736) on the Tecsuns sometimes, and get a better overall result than the Murata de-tuned by only a single khz. The limiting factor is whether or not there is still enough carrier frequency to modulate the signal: otherwise, the Donald Duck distorted audio results. This requires either a healthy signal for the desired target (i.e., a near-local), or the use of a regenerative loop like the Super SAT which when tuned to the carrier frequency supplies the carrier that the DSP filter is otherwise largely cutting off. Using a regen loop like this, tight trans-oceanic targets (like 729 under a 730 khz domestic) are much better IMO. The Murata filter is just too tight to allow this.

Thanks - Kevin

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

Hello all,

I noticed that on my PL-380, I can detune up to one filter width and still get good sound quality. For example, if I'm listening to 1070 kHz with the 2 kHz filter, I can tune as low as 1068 kHz or as high as 1072 kHz.

In the past, I've always used the rule that you can detune up to one half the filter width. This is how is works with my Satellit 800 and Icom R75 for example. With the 4 kHz filter selected on the Sat 800, I can detune by 2 kHz.

This leads me to believe that on the Tecsun DSP radios, the specified filter width is half as wide as it is on my other radios. For example, the 2 kHz DSP filter is equivalent to a 4 kHz filter on my other radios.

On most of my radios the filter width is specified using both sidebands; on the DSP radio it appears to be specified using just one sideband. I always thought the former was the standard way of measuring filters. Is this not the case?

Regards,
Gary


Gary Kinsman
 

Thanks for your explanation, Kevin.

--- In ultralightdx@yahoogroups.com, "dhsatyadhana" <dhsatyadhana@...> wrote:

Hi Gary:

You've got it spot-on: the DSP bandwidth is specified per sideband, not for the whole thing like most filters. So, the 1 khz bandwidth is actually a 2 khz (total) in normal parlance.

At the beach last time listening to split frequency targets, I did some comparisons between DSP filtering and the outstanding 2.4 khz Murata filter that has found its way into a lot of Eton e100's and CCrane SWP's. The Murata is tighter than the 1 khz (2 khz total) filter on the DSP radios, so kudos to Murata for still having the best filtering. For instance, listening to 738 under a domestic on 740, the Murata has less slop when the receiver is detuned by a khz to 737. So, the 1 khz DSP setting might be better compared to a 2.8 khz "regular" filter - still pretty darn good.

Since the 1 khz DSP filter does allow a little more signal through, one can detune by 2 khz (i.e., down to 736) on the Tecsuns sometimes, and get a better overall result than the Murata de-tuned by only a single khz. The limiting factor is whether or not there is still enough carrier frequency to modulate the signal: otherwise, the Donald Duck distorted audio results. This requires either a healthy signal for the desired target (i.e., a near-local), or the use of a regenerative loop like the Super SAT which when tuned to the carrier frequency supplies the carrier that the DSP filter is otherwise largely cutting off. Using a regen loop like this, tight trans-oceanic targets (like 729 under a 730 khz domestic) are much better IMO. The Murata filter is just too tight to allow this.

Thanks - Kevin


Marc Coevoet
 

Op 19-12-10 22:15, dhsatyadhana schreef:
Hi Gary:


At the beach last time listening to split frequency targets, I did some
comparisons between DSP filtering and the outstanding 2.4 khz Murata
filter that has found its way into a lot of Eton e100's and CCrane
SWP's. The Murata is tighter than the 1 khz (2 khz total) filter on the
DSP radios, so kudos to Murata for still having the best filtering. For
instance, listening to 738 under a domestic on 740, the Murata has less
slop when the receiver is detuned by a khz to 737. So, the 1 khz DSP
setting might be better compared to a 2.8 khz "regular" filter - still
pretty darn good.

I am not sure is the slop coming from the 740Khz station, or is the slop coming from the detoriation of all signals?

Marc

--
What's on Shortwave guide: choose an hour, go!
http://shortwave.tk
700+ Radio Stations on SW http://swstations.tk
300+ languages on SW http://radiolanguages.tk


Kevin Schanilec
 

Hi Marc:

It's coming from 740. Broadcast signals are dual sideband, meaning that there is essentially identical information on both the upper sideband. US signals are required to fit within a 10.2 khz total bandwidth, meaning that it extends plus/minus 5.1 khz on either side, thus "sideband". As a result, treble response is basically limited to 5.1 khz (it used to be 7.5 khz, and still is in Canada, which is why some Canadian stations sound a lot better IMO)

In the case of a domestic on 740, their lower sideband extends between 735 and 740, meaning that a TP on 738 is being severely trounced upon. However, the 738 itself has a lower sideband from 733 to 738, so tuning down to 737 or even 736 gets you farther away from 740 while listening to 738's lower sideband. There will still be some of 740's lower sideband mushing things up, but it will be diminished compared to tuning to the TP right on 738.

Hope this helps - Kevin

--- In ultralightdx@yahoogroups.com, Marc Coevoet <sintsixtus@...> wrote:

Op 19-12-10 22:15, dhsatyadhana schreef:
Hi Gary:


At the beach last time listening to split frequency targets, I did some
comparisons between DSP filtering and the outstanding 2.4 khz Murata
filter that has found its way into a lot of Eton e100's and CCrane
SWP's. The Murata is tighter than the 1 khz (2 khz total) filter on the
DSP radios, so kudos to Murata for still having the best filtering. For
instance, listening to 738 under a domestic on 740, the Murata has less
slop when the receiver is detuned by a khz to 737. So, the 1 khz DSP
setting might be better compared to a 2.8 khz "regular" filter - still
pretty darn good.

I am not sure is the slop coming from the 740Khz station, or is the slop
coming from the detoriation of all signals?

Marc

--
What's on Shortwave guide: choose an hour, go!
http://shortwave.tk
700+ Radio Stations on SW http://swstations.tk
300+ languages on SW http://radiolanguages.tk


seta <michael.setaazul@...>
 

10 kHz channel spacing, but with two 5.1 kHz sidebands.
There must be a good reason for this - no?
And how do adjacent channels sound in Canada?

Michael

----- Original Message --------------------------------------------------

From: "dhsatyadhana"

Hi Marc:


US signals are required to fit within a 10.2 khz total bandwidth, meaning that
it extends plus/minus 5.1 khz on either side, thus "sideband". As a result,
treble response is basically limited to 5.1 khz (it used to be 7.5 khz, and still is
in Canada, which is why some Canadian stations sound a lot better IMO)


Kevin Schanilec
 

Not sure how/why the FCC chose 5.1 khz - perhaps they were planning ahead to make AM IBOC untenable :-) It seems like stations are generally 20 khz or more apart in a given geographic area, so letting a station bleed 0.1 khz into the next adjacent channel isn't a big deal.

Canada's MW band has always been less densely populated than the US's, and with more and more Canadian stations going silent, any adjacent channel interference is likely pretty minimal. The FCC went from 10 to 7.5 to 5.1 khz audio as the US band swelled with new stations - it may be interesting to see if they loosen it back up again as stations go silent???

Kevin

--- In ultralightdx@yahoogroups.com, "seta" <michael.setaazul@...> wrote:

10 kHz channel spacing, but with two 5.1 kHz sidebands.
There must be a good reason for this - ¿no?
And how do adjacent channels sound in Canada?

Michael


----- Original Message --------------------------------------------------

From: "dhsatyadhana"

Hi Marc:


US signals are required to fit within a 10.2 khz total bandwidth, meaning that
it extends plus/minus 5.1 khz on either side, thus "sideband". As a result,
treble response is basically limited to 5.1 khz (it used to be 7.5 khz, and still is
in Canada, which is why some Canadian stations sound a lot better IMO)


Russ Edmunds <wb2bjh@...>
 

As Kevin points out, the 10 kHz spacing isn't really relevant. In any given market, spacing is almost always 40 kHz between stations. Regionally, it can be 20 kHz., however at the kinds of distances involved, it could be ten and you probably wouldn't notice that extra 0.1.

Russ Edmunds
15 mi NNW of Philadelphia
Grid FN20id

FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'; Grundig G8
AM:  Modified Sony ICF 2010's barefoot


--- On Sun, 12/19/10, dhsatyadhana wrote:

From: dhsatyadhana
Subject: [ultralightdx] Re: Filter width on DSP radios
To: ultralightdx@...
Date: Sunday, December 19, 2010, 7:22 PM

 

Not sure how/why the FCC chose 5.1 khz - perhaps they were planning ahead to make AM IBOC untenable :-) It seems like stations are generally 20 khz or more apart in a given geographic area, so letting a station bleed 0.1 khz into the next adjacent channel isn't a big deal.

Canada's MW band has always been less densely populated than the US's, and with more and more Canadian stations going silent, any adjacent channel interference is likely pretty minimal. The FCC went from 10 to 7.5 to 5.1 khz audio as the US band swelled with new stations - it may be interesting to see if they loosen it back up again as stations go silent???

Kevin

--- In ultralightdx@..., "seta" wrote:
>
> 10 kHz channel spacing, but with two 5.1 kHz sidebands.
> There must be a good reason for this - ¿no?
> And how do adjacent channels sound in Canada?
>
> Michael
>
>
> ----- Original Message --------------------------------------------------
>
> From: "dhsatyadhana"
>
> Hi Marc:
>
>
> US signals are required to fit within a 10.2 khz total bandwidth, meaning that
> it extends plus/minus 5.1 khz on either side, thus "sideband". As a result,
> treble response is basically limited to 5.1 khz (it used to be 7.5 khz, and still is
> in Canada, which is why some Canadian stations sound a lot better IMO)
>