The AM Forum

Hi!

Perhaps no surprise... but I did something interesting today (beyond troubleshooting and making repairs on intermittent problems with various pieces of equipment I own)

I acquired a 192 ksps audio interface (essentially a sound card) that connects to my computer using Firewire (IEEE 1394). It is an M-Audio Profire 610

After an hour or so of figuring out which settings to use to get it to work properly... I had it up and running with Flex Radio's Power SDR application.

Now for the interesting part (at least for me):

I connected the 50kHz  i.f. output of my Drake R-4C directly to the input of the Profire 610 (no mixer). With 192 kHz sampling rate... the combination of the Profire 610 and the Flex Radio software had no problem accepting the 50kHz i.f. signal, displaying the spectrum, and demodulating it in the usual modes (AM, sunchronous AM, ...).

Obvious in theory... but interesting in practice.

Next experiment... replace the 8kHz wide  first i.f. filter in the Drake R-4C with a much wider bandwidth  "roofing filter" ... and get an even wider 50 kHz-centered panadapter display from the 50kHz i.f. output. The interesting part (for me) is the "marriage" of old and new equipment.

Best regards
Stu

Stu

Interesting. Don't know how wide you're planning to go with the new filter and whether your receiver is stock or not, but as I recall the DR for a stock R4C at 2kHz was in the mid 50's. Be careful how wide you open that barn door.   :-\

Jay

Good point!

Any thoughts on where in the rf input => demodulated audio chain the DR-limitation is in the R-4C?

My R-4C came with most of the Sherwood mods... but those won't have any impact on the signal at the 50kHz i.f. [I did notice that the stock AM demodulator (per the schematic and the actual performance) in the R-4C is really poorly designed. The top end started to roll off at around 1500 Hz, and the bottom end started to roll off at around 1000 Hz ( :o) I had to increase the value of the AM envelope detector's output DC-blocking capacitor to open up the bottom end, and I had to add a resistor in parallel with the capacitor in the AM envelope detector in the to open up the top end. It sounds much better (when I use it) now]

Separate question...

Can I change the total number of samples used to calculate each sweep of the spectral display in Power SDR? With a 192 ksps sampling rate, I need 4x as many samples in each FFT computation in order to keep the same spectral display resolution.

Best regards
Stu