[Collins] Connecting a Panadapter to an S-Line Receiver

[Dr. Gerald N. Johnson]

I presume the FunCube has very good sensitivity. Several places would 
work. The grid of the second mixer, coupled with a small capacitor, 
probably less than 5 pf, or the plate of that tube similarly coupled. 
The grid of the second mixer sees a pass band of about 2.955 to 3.155, 
probably wider. Its upside down because the crystals are on the high 
side for the first mixer. The plate of the 2nd mixer (or input to the 
mechanical filter) probably won't have as much bandwidth as the grid and 
is centered on 455 kHz which is a more usually place for panadapter 
connections.

There would be a wider spectrum off the plate of the first mixer before 
the band pass filter of the first IF, or even broader off the grid of 
the first mixer.

The bandpass the FunCube would see at the first mixer grid is set by the 
RF tuning coils. Peaking them is noticeable when changing to opposite 
ends of some bands. That would be signal frequency.

The pass band at the first mixer plate would be that 2.955 to 3.155 
upside down but would be broader there than at the grid of the 2nd mixer 
after the bandpass filter.

The spectrum at the output of the 2nd mixer centered on 455 kHz will 
still be upside down.

If you can't get enough signal with 5 pf coupling capacitor you could 
use more but then should realign that tuned circuit and that can be 
touchy when the ceramic trimmers are stuck. Alternatively you could add 
a preamp with an low noise MMIC like a MSA-0685 or use a FET as a source 
follower. But I think the funcube will have adequate signal after the RF 
stage or mixers because of the gain in each of those stages.

Picking off at the first IF frequency you always see the same frequency 
range there that changes with the band/crystal selection.

Picking off at the first mixer grid you see what the RF section is tuned 
to and so have to change the center frequency of the funcube when you 
change band segments.

Picking off at the second mixer plate you always see the spectrum 
centered on the frequency the receiver is tuned to.

It may take a little software adjustment to make the funcube display 
show the higher received frequency on the right side of the display, but 
that may not be difficult or something impossible to get used to.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 11/30/2013 7:42 PM, Bob Myers wrote:
> Howdy,
>
> Does anyone have experience using an SDR FunCube Pro+ Dongle USB receiver as a panadapter/analyzer with an S-Line receiver? I'd like to connect the SDR Dongle to my 75S-3 to provide Spectrum View of band segments.
>
> Are there suggestions for a connection point in a 75S-3 for an Analyzer?
>
> The Dongle works very well with the 9 MHz output of my more-modern transceiver.
>
> Thanks,
>
> Bob W1XT  Sun City West, Arizona
>