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Has anyone ever tried to sweep the 50Khz I.F. in the R4B with a spectrum analyzer?? WA8SAJ had a powerpoint presentation a few years ago showing screenshots using his SA to sweep the 50 Khz I.F., but he gave no real explanation of how he performed the test and adjustments for the passband curves. I have tried to reproduce his SA sweeps without success just can't seem to find the right input for the tracking generator and output from the R4B to the SA? input.? Anyone have success performing this procedure?

Dave

Guess I should mention I have the exact same spectrum analyzer as WA8SAJ used in his test.

50 KHz is hard. Most analyzers that could fall into ham hands don't go down that far. I have an old HP that goes down to 20 Hz but it would anchor a decent size boat.

73

-Jim
NU0C

On Sun, 19 Mar 2023 17:17:32 -0700
"W6MQI via groups.io" <w6mqi@...> wrote:

Has anyone ever tried to sweep the 50Khz I.F. in the R4B with a spectrum analyzer?? WA8SAJ had a powerpoint presentation a few years ago showing screenshots using his SA to sweep the 50 Khz I.F., but he gave no real explanation of how he performed the test and adjustments for the passband curves. I have tried to reproduce his SA sweeps without success just can't seem to find the right input for the tracking generator and output from the R4B to the SA? input.? Anyone have success performing this procedure?

Dave

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When I sweep something like this I feed in the tracking generator signal, preferably a stage before, through with around a 10k resistor. ?The I preferably use an FET probe to pick off the signal that goes back into the spectrum analyzer. ?A 10X passive probe may work but the termination will be wrong. ?

I use an HP 3585A which is good from audio through 40 MHz. Rob, NC0B

I have a 3585B. A beautiful instrument. I also have a 8594E with TG and narrowband options that is a bit more portable. It's spec-ed down to 9 KHz but I've never pushed it that low. My NanoVNA claims coverage to 50KHz. Might work OK on a Drake low IF.

73

-Jim
NU0C

On Mon, 20 Mar 2023 00:39:54 +0000
"Rob Sherwood" <rob@...> wrote:

I use an HP 3585A which is good from audio through 40 MHz. Rob, NC0B

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For my single conversion Hammarlund alignments I make extensive use of an SA - the Hammarlund folks at the factory were funny about that. Anyway, any of the new generation SA's like Siglent, Rigol, etc., will sweep +/- 50 kHz.

Boy that was a fast response thanks guys for the tips. The SA I have is a Rigol 815TG? which is the same unit WA8SAJ uses so figured I was good to go unfortunately I'm a little new to spectrum analyzers' operation. The first test I did was the 5645 Khz sweep with the SA connected through a blocking cap to pin1-V2 then used a small coil of insulated wire to basically sniff on the underside of V3. There was enough signal to draw a pattern on the SA seemed to work really well. Think I will revisit the 5645 test again without a direct connection to see if there's any difference in SA response.?
?In regards to the 50Khz test, I was directly connecting the TG through a blocking cap in multiple places without success, and from what you all said this is the wrong test setup to use. Was also using a blocking cap for the SA input as well I will refine my connections and report back as long as I can find the right test points for TG and SA input.

Dave

Hi Dave!
I use an Elecraft K3 with a P3 daily, and when I refurbished my old(ish) B-twins a few years ago I wanted to see the effect of the variable passband filtering, so that meant looking at the 50 kHz IF.? I used a small impedance buffer preamp mounted under the chassis of the R-4B near the 50 kHz amp V5 feeding an SMA in the 'Spare' jack position on the rear skirt and feed an .? It was the only one I could find which went below 100 kHz, indeed it will receive as low as 500 Hz.

Of course there are issues: the 50 kHz LO feeds through to V5 and shows up as a constant peak in the display, but that is a minor complaint.? In general it works well, but those of us spoiled by steep crystal filters and DSP IFs, or in my case the will find the resulting passband shape factor to be somewhat...lumpy may be a good word?? I have been a broadcast engineer for 40 years and have serviced more FM transmitters (I love my old Gates FM-1H!), receivers and ham gear than I care to remember so although I will not claim to be the most expert RF aligner, I do have a passing familiarity with RF and IF alignment.? This being said, I ran through a full alignment as per the manual and the receiver works gangbusters.? Sensitivity is on par with my K3 but sounds SOOOO much better and the analog passband tuner is a thing of beauty compared to the DSP filtering in the K3 which gets harsher the more narrow you squeeze it.? Despite this fine performance, the 50 kHz IF passband shape is still not as nice as a crystal filter...I'll bet NC0B would see much better results on his modded R-4C, still it is nice to be able to see the band activity on my PC, it is usable and fun to see.

Cheers & 73,
Howie / WA4PSC