What Signal Generator do you use?

[Lkaskel]

Ok, so the life of a hobbiest. I am aligning a radio and having trouble with the receive alignment. I play with everything but it turns out that my HP 8660C signal generator is not working correctly. When I go from -80dB to -70dB the signal drops out. It's a battleship of a piece of equipment but it may be time to replace it on a budget. What are you using that would be considered a budget buy?

 

[brandon7861]

It is just a radio, try fixing it. Since it works on -80dBm, all of the synthesizer stuff works. That narrows the problem down to the attenuators and the switches between them. I bet there's a schematic out there for it somewhere.

This is where one of those carlson super probes or other audio tracing probe would shine. Set that thing to output modulated AM signal and follow it until you lose it.

 

[brandon7861]

Ok, here we go, found it. The attenuator schematic was in a different manual.

A13 is the attenuator module and it does use relays.

See how with no attenuation, the output is +10dBm? That means to have the output set to -80dBm requires 90dB of attenuation, or 2 of the 40dB attenuators and the one 10dB attenuator switched in. If going from -80dBm to -70dBm makes the signal go away, it suggests the relay that bypasses the 10dB attenuator is bad.
To test my bad relay theory, see if you can set it to --100dB (two of the 40dB attenuators, the 20dB attenuator and the 10dB attenuator in line), should have signal, and then go to --90dB (which would bypass the 10dB) and see if the signal disappears.

 

[Lkaskel]

Ok, here we go, found it. The attenuator schematic was in a different manual.

A13 is the attenuator module and it does use relays.
View attachment 72179
See how with no attenuation, the output is +10dBm? That means to have the output set to -80dBm requires 90dB of attenuation, or 2 of the 40dB attenuators and the one 10dB attenuator switched in. If going from -80dBm to -70dBm makes the signal go away, it suggests the relay that bypasses the 10dB attenuator is bad.
To test my bad relay theory, see if you can set it to --100dB (two of the 40dB attenuators, the 20dB attenuator and the 10dB attenuator in line), should have signal, and then go to --90dB (which would bypass the 10dB) and see if the signal disappears.

Thanks Brandon,
I'll check it out tonight and keep you posted.

 

[NODENS]

TinySA Ultra: Low budget, small and nice signal generator and spectrum analyzer for cbradio hobby

 

[Smiley429]

I use an IFR / Marconi that does a good job for me to align radios.

 

[guitar_199]

Well... I came in to answer the question in the Subject line.....

I have two...
A B&K Precision 2040 CB Signal Generator for basic CB/11m band work
and if that doesn't do it.....
A Boonton 102F 500 MHz AM/FM RF Generator that covers anything else up to 500 Mhz

Then I saw.... "a budget"

On that, I too lean in the direction of the Tiny SA. Not a lot of bucks but a pretty good bit of capability.

 

[Pez]

Hopefully you can fix the HP, but if not I would also recommend the Tiny SA Ultra. It gives you a lot of bang for the buck. It's hard to beat for the price, but you will want to add some external attenuation to bring the generator levels down low enough for some tests.

If you are looking for an even more budget HF generator, the Feeltech FY6900 is pretty good. It works to 100MHz depending on the version, and runs on an internal 10MHz TCXO reference. Doing a modification to accept an external 10MHz reference is pretty easy. It supports AM and FM modulation too. And of course also does all of the 1KHz tone / 2-tone generation you might want to do at the audio level.
You will again need to use external attenuation to get your typical HF signals low enough for some jobs, but it works pretty well and it is very cheap. I haven't tested how accurate the output levels are as I have better quality generators available, but for frequency stability and features it's great for the money.

 

[Michael M]

Motorola R26XX Series Mobile Tester
IRF FM/AM-1200 Service Monitor

 

[brandon7861]

I have the 60MHz version of this one. The only reason I mention it here is to tell you to avoid it in your search. Looks nice, but it sucks. Ask me why it sucks if you really want the thread cluttered up. It took some internal modifications to make it usable for radio work.

 

[Cable Guy]

Well, another thread that costs me money, just what I needed lol. I use an old HP sign gen, the model escapes me atm, but it's old. Now after this thread landed me on the Amazon tinysa ultra listing, I'm a little lighter in the wallet. I have been waiting to come across a sa that was affordable. The added sig gen function is nice. Just need something, anything to tell the wife. Not only is this hobby of ours hard, it's expensive.

 

[brandon7861]

Just need something, anything to tell the wife.

Just say "I know sanity is important to both of us, so I want you to go to the spa". She will be in such a good mood when she returns that she won't even notice the new SA sitting there..

It might also help if you accidentally leave a browser tab open giving the impression you were also looking at jewelry.

 

[Gman]

HP606A. All tube. Let it warm up for an hour, then its stable.

 

[Lkaskel]

So here is the update for now. The attenuator is bad. The relays act a lot like a solenoid and one of them is bad. I did order a replacement off eBay and it should be here this weekend. We shall see. These HP higher end generators are built like a spaceship. Holy smokes is it impressive......

 

[Michael M]

Motorola R26XX Series Mobile Tester
IRF FM/AM-1200 Service Monitor

Thanks for the heads up. Looks nice, but......