From: Garey Barrell 
Subject: Re: [drakelist] R-4B Good for AM ???


Garey Barrell  made an utterence to the drakelist gang
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Al -

To receive AM on the R-4B you will want to tune in the AM signal in what 
is known as "exalted carrier" mode.  All this means is that you tune the 
the AM signal as if it were an SSB signal, i.e., product detector on, 
carrier at zero-beat.  Then you can use the Passband tuning to choose 
either sideband, but only one, to listen to.

The R-4B has a 6 kHz "roofing filter" in the first IF, and the maximum 
bandwidth for the Passband tuner is 4.8 kHz.  BOTH these filters have 
gently sloping skirts rather than the "drop off the edge of the table" 
crystal filters today.  But there really is only room for one sideband 
at a time.  On the other hand, using the Passband tuner you can listen 
to ANY 4.8 kHz segment at any one time.

One problem with this scenario is that many AM signals are not stable 
enough to STAY at zero-beat, so you have to keep retuning.

The R-4C, on the other hand, has an 8 kHz roofing filter, and so the 
"native" bandwidth as delivered from the factory was 8 kHz, since the 
"optional" AM filter position had a resistor in place of the optional AM 
filter.  There were available filters of 4 kHz, 6 kHz and 8 kHz to plug 
into this spot.

If "full fidelity" AM is what you are looking for, consider instead 
something like an HQ-129X (old), HQ-140X (not so old), NC-300 (NOT an 
NC-303), 75A-1 or 75A-2, or 51J-3.  ANY of these will give superior 
performance  _on AM_  to an R-4B, IF "full fidelity" AM is what you 
want, at a penalty of size and/or expense for the Collins units.

For  _communications quality_  AM, the R-4B will do an outstanding job!!

73, Garey - K4OAH
Atlanta


n7ioh wrote:
> 
> n7ioh  made an utterence to the drakelist gang
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>    Hi, I am currently trying to decide if the R-4B would be good for AM 
> reception in the ham bands.  I would like to use the radio with my 
> Johnson Viking Ranger II.  I am currently leaning toward the R-4B 
> because of cost and all the good things I have heard and read about it.  
> I was told that the R-4B filters may be to narrow for really good AM?  
> Others have said that this is not true and that the R-4B would make a 
> fine receiver for AM.  Anyone use this receiver for AM and are there any 
> mods that I should or could do to improve the AM?  I like everything 
> about the R-4B just have concerns about using it for AM.  I will also 
> use the radio for SSB and some light CW use so I don't want to degrade 
> the radio in these areas.  Thanks in advance for your help and input.
>                                              Al N7IOH
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