[R-390] Image problem solved

[Jon Schlegel]

Tony,
Please see inline.

At 11:23 PM 10/24/2007 -0600, you wrote:
>I was using an BNC to twinax adapter which grounds one side of the 
>balanced connection. When I remove this and run the signal generator 
>or antenna two the balanced pins without tying one side to the 
>chassis, I can see nothing on the spectrum analyzer.

So it sounds like you are saying that you are feeding the two 
balanced twinax pins in common mode, i.e. the twinax pins are tied 
together and fed with the center conductor of the coax.  Coax shield 
to radio case/ground.  Is this correct?


>  That is, With thereceiver tuned to 3 Mhz and the sig gen at 
> 1.5MHz, I see nothing at the input to the RF amplifier.
>
>Looking at the schematic, they show a field change which grounds one 
>side of the balanced input but SWAPS J105 AND J106.

It sounds like the intent of the field change is to ground one side 
of the balanced input and transfer the other side of the balanced 
input so that it would appear at the single ended connector referred 
to at least on my schematic as "J103 Whip Unbalanced".  Is this correct?


>  They were not swapped in my receiver. Swapping them and then going 
> back to my adapter gives much improved performance. I don't hear 
> the 1650KHz broadcast station at 3.3MHz any more but I can again 
> see some a 1.5 MHz signal at the RF amp input when the receiver is 
> tuned to 3 MHz. But it is way down from before. The best 
> performance for the preselector seems to be with J105 and J106 not 
> swapped  and neither side of the balanced input grounded to the 
> receiver chassis.

I'm not getting this part because it sounds like the balanced input 
is being fed common mode.  Maybe I'm misunderstanding what you mean 
swapped and not swapped.

BTW - I'm still waiting for the eBay seller to ship my radio. 
GRRR  &$@)&@!$%^.  If I had the darn thing to look at it probably 
wouldn't be confusing!

Jon





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