[R-390] Image problem solved

[Jon Schlegel]

Tony,

Can you give a page/figure reference for the field change?  I'm 
looking at "TM 11-856A  Dept. of the Army, January 1956" and I'm not 
seeing the field change.  My copy may be too old.  If so, might you 
be able to direct me to a newer copy?

Jon


At 06:36 AM 10/25/2007 -0600, you wrote:
>No, I am not feeding the two balanced inputs the same signal. I tied 
>the shield of the coax to one sine of the balanced input amd the 
>center of the coax to the other side. I just don't tie either side 
>to chassis at the same time. This seems to give the best results.
>
>The field change connections look odd to me as well but I tried it 
>vecause it was shown that way on the schematic.It does seem to work 
>much better, but not as well as lifting the chassis ground from one 
>side of the balanced input.
>
>The schematic I am referring to is in TM-11-856a.
>
>Tony
>
>
>----- Original Message ----- From: "Jon Schlegel" <ews265 at rochester.rr.com>
>To: <r-390 at mailman.qth.net>
>Sent: Thursday, October 25, 2007 12:03 AM
>Subject: Re: [R-390] Image problem solved
>
>
>>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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