[R-390] Image problem cause... sort of

[Bob Camp]

Hi

I would be surprised if the 392 has more front end selectivity than  
the 390A up to the first RF amp plate. It's been a long time since I  
was last inside a 392 though. The 392 is a "390 not an A" clone in  
that it has two RF stages and a second deck of RF tuning in front of  
the first mixer. That should give a bit more selectivity in front of  
the mixer.

Bob


On Oct 23, 2007, at 11:04 PM, Tony Casorso wrote:

> I believe I have a handle (part of a handle) on my image problem. I  
> compared the preselector selectivity of my R-392 to the R-390a and  
> the R-392 is way way better.
>
> I put in a signal from the generator on the balanced antenna input  
> and put the spectrum analyzer on the grid of the first RF stage  
> through a 10x probe and a small capacitor. With the generator at  
> 1.5 Mhz I tune the receiver to 1.5Mhz and peak the antenna control.  
> I note the amplitude of the 1.5MHz signal on the analyzer and then  
> tune the reciver to 3 MHz. On the 390a the 1.5MHz signal drops less  
> than 20db. On the 392 it drops over 50db.
>
> I also note that the peaking with the antenna trimmer is much  
> sharper in the 392 than with the 390a.
>
> I want to look at some other bands and see if it is like this  
> everywhere.
>
> Tony
>
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