TinySA/TinySA Ultra for AM/FM Receiver Alignment

[A Sound Mind]

Hi All.
(Please let me know if this is the correct forum for this subject)

I just picked up a TinySA Ultra hoping to use if for alignments.
This device is primarily used as spectrum analyzer, but it also has powerful function generator capabilities.
However, I haven't been able to locate much info on how to use it for receiver tuner calibrations.
Unfortunately, it can't perform FM multiplex calibrations and isn't equipped to output to a stereo analyzer.
Can anyone here give me some pointers on using this instrument? I believe I've exhausted all the YouTube videos on it.
And I'd appreciate recommendations for possible alternatives that won't vaporize my pocketbook.
I only get three or four receivers a year to service, so I need to justify the investment.

 

[Brian1970]

I got one for Christmas but haven't had a chance to figure it all out yet. You're right that it can't do MPX but should work well for AM & FM Mono. If you can find a way to generate MPX at baseband, it looks like you can feed that into the Tiny SA to modulate the RF signal. I think I read somewhere that it might be possible to use a computer soundcard to generate an MPX signal at baseband but haven't tried it.

 

[A Sound Mind]

I got one for Christmas but haven't had a chance to figure it all out yet. You're right that it can't do MPX but should work well for AM & FM Mono. If you can find a way to generate MPX at baseband, it looks like you can feed that into the Tiny SA to modulate the RF signal. I think I read somewhere that it might be possible to use a computer soundcard to generate an MPX signal at baseband but haven't tried it.

The unit only has one usable SMA port, so I don't see how an external signal can be mixed in.

 

[Brian1970]

The unit only has one usable SMA port, so I don't see how an external signal can be mixed in.

I saw the external option in the menu and read too much into it. Should have googled it. Looks like that external option has some pretty limited functionality.

 

[Bob@FM]

Don't own one, but looks like the TinySA may be able to do the RF front end alignment, and that's about it. This is the alignment step where you adjust the L and C on the RF front end with a low RF input level, and make sure the dial tracks properly. It's mostly a spectrum analyzer, and apparently decent constant wave generator - but a poor FM generator - it appears the FM mode is "approximated" so likely has very high distortion, which makes it useless to align an FM detector.

The other alignment steps, which depend on the type of "receiver" you have, require low distortion wide bandwidth FM, and FM MPX generator.
Maybe OK for old mono radios and such, but for better modern tuners, you need a proper FM MPX generator - ST-1000A, VP-8174A, VP-8175A, etc. For older stuff, SG-165 with sweep.

You can get "close" FM MPX generation, perhaps, if you use a little car FM stereo converter, which may have both analog and bluetooth inputs. I reviewed a few of these very low cost units a year or two ago. The main problem with these is the RF signal is way too high, no cabled RF output, so RF needs to be greatly attenuated to be useful. And you need to know what the heck you are doing to use something like this, not great for a novice to learn on. See "$16 FM Transmitter" here -

main@FMtuners.groups.io | $16 FM transmitter

fmtuners.groups.io

 

[A Sound Mind]

I'm a retired microelectronic design engineer, but a rookie when it comes to RF.
Nowadays, I generally work on antique and vintage radios, record players, etc, and only come across a few stereo receivers a year to work on, which isn't enough to justify investing hundreds in RF test equipment beyond all the equipment I have.
Despite that, these receivers usually end up working quite well and I haven't had any complaints in the past ten years or so.
But right now, I'm working on a Pioneer SX-939 and I can't get the FM stereo to properly kick in.
Everything else on this receiver is working fine.
I just need some help getting over this hurdle.

 

[Bob@FM]

The SX-939 is worth fixing. You can look at the FM detector output from pin 6 of the HA1137 on the 4 CH MPX out jack on the back panel. Be sure that same signal is reaching pin 2 (input) on the HA1156 MPX chip. It goes through the mute section in between, through a 2SK30A FET.

You can also check the VCO pot VR1 - may be dirty, or need tweaking. With strong stereo station, move VR1 both CW ans CCW slowly while watching for stereo to kick in. Set it in the middle. You can do a lot of stereo trouble shooting by injecting an exact (use a counter) 19 kHz signal into pin 2 on HA1156, ~200 mV rms level. If stereo is working, it will turn on this way. The key caps involved are C36, C37, C38. Also check pins 8,9 for proper DC levels. The HA1156 data sheet has more info. Sometimes those chips go bad, too.

You can use an FM car stereo adapter to adjust stereo separation. Set it up 20 ft away, and play a 1 kHz test signal into the stereo adapter. use only L input, then R, to do the separation. The ones I tested are good for maybe 40 dB separation, way better than doing it by "ear".
You can only get good at this stuff by doing it, making mistakes, and learning. A lot of it involves adapting the alignment steps to what you have. On the older stuff with cweramic filters like this unit, you can get pretty far simply using over the air stations, and a car stereo adapter.
Bob

 

[A Sound Mind]

I partially comprehend what you're saying Bob. (200mV rms?) (40dB separation?)
Can I use my HP3312A to generate these signals? I also have a freq counter.
I had played with VR1 and got stereo to kick in near one extreme, but the stereo light barely flickered and the audio became distorted.
Would you please link me to those FM car stereo adapters you mentioned? All I see are lighter socket types.
A video demo of these procedures would be very helpful, but I give them a try.
Thanks!

 

[Bob@FM]

I forgot the model numbers, they are buried in the message thread linked above. You should read that to understand the limits of these things, and finer points too. Short story, The first one tested, Lencent, was powered by a wallwart that supplied 12V power via lighter socket on a cable. That cable effectively works as the transmit antenna.
It gave full control of FM band tuning frequency, and was stable and accurate. You can play bluetooth or SD/USB files. Impressive for the price. I generated a set of FLAC test tones in Audacity, and used those for testing via USB. All the details are in that thread.
Separation is stereo separation, measured in dB. This is important for a transmitter used in testing, to know. It limits the ability to do better than that n the alignment, if possible on a good tuner.
The 3312A is not super stable, but will work, just use a counter and let it both warm up for an hour before using.
Also, forgot to mention - the TinySA has a 50 ohm input. So 10:1 probes for 1M input scopes are no good. You need and active probe with 50 ohm out to use that for RF probing. There is a guy on ebay selling these FET probes from Europe for $30-40. That is the least expensive option. Google this stuff if it's unclear.