Hey, folks.  I am a newbie.  Please explain how I would judge sensitivity, selectivity and quality.  Last night between thunder storms my Tecsun Dr-920c picked up a strong signal from WCBS 880 in NYC at 920 miles.  Traffic reports. That seems like excellent sensitivity to me.  no other stations were bleeding in so that excellent selectivity, right? Some background static was constant but not bothersome.  I guess that is good signal quality.  Am I scoring correctly? Thanks.

I personally find that this is about how radio a compares to radio b in a given location and at given time.

I have had radios that have worked well for me in my location that don't work as well for somebody else at their location.

Paul

On Mon, 7 Mar 2022, 4:48 am , <Jim.rohrer1955@...> wrote:

Hey, folks.  I am a newbie.  Please explain how I would judge sensitivity, selectivity and quality.  Last night between thunder storms my Tecsun Dr-920c picked up a strong signal from WCBS 880 in NYC at 920 miles.  Traffic reports. That seems like excellent sensitivity to me.  no other stations were bleeding in so that excellent selectivity, right? Some background static was constant but not bothersome.  I guess that is good signal quality.  Am I scoring correctly? Thanks.

Atmospheric conditions were strange last night. 

On Sun, Mar 6, 2022 at 3:32 PM Paul Blundell <tanger32au@...> wrote:

I personally find that this is about how radio a compares to radio b in a given location and at given time.

I have had radios that have worked well for me in my location that don't work as well for somebody else at their location.

Paul

On Mon, 7 Mar 2022, 4:48 am , <Jim.rohrer1955@...> wrote:

Hey, folks.  I am a newbie.  Please explain how I would judge sensitivity, selectivity and quality.  Last night between thunder storms my Tecsun Dr-920c picked up a strong signal from WCBS 880 in NYC at 920 miles.  Traffic reports. That seems like excellent sensitivity to me.  no other stations were bleeding in so that excellent selectivity, right? Some background static was constant but not bothersome.  I guess that is good signal quality.  Am I scoring correctly? Thanks.

Selectivity is a combination of the channel selection filter’s bandwidth and how steeply the filter attenuates frequencies outside the filter’s bandwidth.

Narrow filters have greater selectivity, but they’re also narrower than the bandwidth broadcast by the station. When this is the case, the audio’s treble is lost. If the radio is capable of it, then detuning the radio slightly can restore some of the treble. Also, if there is a strong station on an adjacent frequency, choosing a narrow filter setting and detuning a little, in the direction away from the strong adjacent, helps reject the adjacent channel interference.

The reason why it is often impossible to completely reject adjacent channel interference is because the sidebands broadcast by the adjacent station overlap the sidebands broadcast by the station you’re tuned to. There will be splashover no matter how good your radio is

But

It is often possible to completely or almost completely eliminate this kind of interference by using a directional antenna. Loop antennas have two sharp nulls 180 degrees apart. If you can point one of the nulls toward the offending station, its interference can be reduced or eliminated.

Sensitivity is about how weak a signal the radio can receive. Theoretically, the only thing necessary is to have the received signal be stronger than the noise generated internally in the radio. Usually atmospheric noise coming in from the antenna is much higher than this, so increasing the gain does little to help beyond a certain point. Therefore sensitivity is more about signal to noise ratio than it is about how much the radio amplifies. The way to get better sensitivity is by placing the antenna away from sources of noise, and by using an antenna with directional characteristics. If atmospheric noise is coming from all directions, an antenna that is sensitive only to signals coming from one direction will reject much of it. In fact, such an antenna usually has very low signal amplitude, but the noise is even lower, making sensitivity better. 

This explains it very well. I have shown it to a ham friend of mine and he thinks it is spot on.

Sent with ProtonMail Secure Email.

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

On Monday, March 7th, 2022 at 10:46 PM, Robert Conboy <robconboy@...> wrote:

> Selectivity is a combination of the channel selection filter’s bandwidth and how steeply the filter attenuates frequencies outside the filter’s bandwidth.
>
> Narrow filters have greater selectivity, but they’re also narrower than the bandwidth broadcast by the station. When this is the case, the audio’s treble is lost. If the radio is capable of it, then detuning the radio slightly can restore some of the treble. Also, if there is a strong station on an adjacent frequency, choosing a narrow filter setting and detuning a little, in the direction away from the strong adjacent, helps reject the adjacent channel interference.
>
> The reason why it is often impossible to completely reject adjacent channel interference is because the sidebands broadcast by the adjacent station overlap the sidebands broadcast by the station you’re tuned to. There will be splashover no matter how good your radio is
>
> But
>
> It is often possible to completely or almost completely eliminate this kind of interference by using a directional antenna. Loop antennas have two sharp nulls 180 degrees apart. If you can point one of the nulls toward the offending station, its interference can be reduced or eliminated.
>
> Sensitivity is about how weak a signal the radio can receive. Theoretically, the only thing necessary is to have the received signal be stronger than the noise generated internally in the radio. Usually atmospheric noise coming in from the antenna is much higher than this, so increasing the gain does little to help beyond a certain point. Therefore sensitivity is more about signal to noise ratio than it is about how much the radio amplifies. The way to get better sensitivity is by placing the antenna away from sources of noise, and by using an antenna with directional characteristics. If atmospheric noise is coming from all directions, an antenna that is sensitive only to signals coming from one direction will reject much of it. In fact, such an antenna usually has very low signal amplitude, but the noise is even lower, making sensitivity better.
>
>