Signal Generator for SSB - Page 1
Forum section: electronics / testgear

author: ErnieEngineer
author_rank: Contributor
timestamp: March 17, 2014, 11:16:44 pm
content: Hi,There many synthesized signal generators on the market that do AM, FM, and phase modulation. I just purchased an HP 8648A for example. I can't find a single model that does SSB modulation. There has to be something out there! Ideally it would be reasonably priced too. I know I can use an actual radio, but that's not the point. I need to do actuate measurements . Any ideas what would work?

author: VK5RC
author_rank: Unknown
timestamp: March 18, 2014, 12:27:27 am
content: One technique is to use a DDS type of software defined radio, the hpsdr group (associated with tapr) produced an exciter that can produce I think around a few hundred milliwatt level output with reasonable (low) phase noise on the hf frequency band. The signal generators that have all the modulation modes start really climbing in price.

author: ErnieEngineer
author_rank: Contributor
timestamp: March 18, 2014, 12:57:42 am
content: Just found this (what you are talking about)https://www.tapr.org/kits_PL.html. The funny thing is, I can't find a SSB generator at any price from Agilent or rohde and schwarz ,etc. Is there anything commercial out there? Not that I can afford it, just curious .Also What is the advantage of using the PennyLane exciter VS a high quality SSB radio transmitter? Either way I would have to use a variable attenuator and calibrate the output with a power meter I believe.

author: G0HZU
author_rank: Super Contributor
timestamp: March 18, 2014, 01:05:48 am
content: Normally, you can just use a basic sig gen in cw mode to generate a single tone SSB signal. If you want two tones you can combine two sig gens. Or are you planning to send human speech as the SSB modulation?I suppose you could use an IQ sig gen and send in your (speech or test tone) modulation to the I and Q inputs to get an SSB signal from a suitable generator. But this kind of generator will be expensive and I've not tried to do this myself.I usually use two sig gens and a combiner and send two cw test tones to mimic a two tone modulated SSB signal. If there is 3dB loss in the combiner then I just take this into account when setting the levels from the two sig gens.

author: w2aew
author_rank: Super Contributor
timestamp: March 18, 2014, 02:37:18 am
content: Quote from: G0HZU on March 18, 2014, 01:05:48 amditto.

author: GK
author_rank: Super Contributor
timestamp: March 18, 2014, 03:01:57 am
content: If you want to use an audio modulation source your options are limited. DSB is easy as all you need is a multiplier. SSB on the other hand requires filtering of one sideband, and that isn't easy to do unless your requirements can be met with a fixed operating frequency.

author: VK5RC
author_rank: Unknown
timestamp: March 18, 2014, 03:02:10 am
content: I haven't noticed that the sig gens don't do ssb until you pointed it out , I think the phase noise may be a bit better out of of a direct up convertor but am not sure, if you really want to know, there is a hpsdr blogg site and the answer may be there, I think a good ssb transceiver looks pretty good value for money, good attenuation needed.

author: GK
author_rank: Super Contributor
timestamp: March 18, 2014, 03:09:17 am
content: ALL signal generators do continuous tone SSBSome of those with a VCA input can also do DSB (if the VCA input range is bipolar - otherwise they can only do AM).

author: VK5RC
author_rank: Unknown
timestamp: March 18, 2014, 03:37:27 am
content: I might be confused but isn't single tone ssb just cw, either up (usb) or down (lsb) by the tone frequency from the suppressed carrier? I was thinking of at least dual tone ssb.

author: GK
author_rank: Super Contributor
timestamp: March 18, 2014, 04:06:52 am
content: Quote from: VK5RC on March 18, 2014, 03:37:27 amYes it is. A signal generator (with a bipolar VCA input) capable of DSB generation could even be used as twin-tone SSB source.

author: KJDS
author_rank: Super Contributor
timestamp: March 18, 2014, 09:15:38 am
content: If you want a general sig gen capability with audio on SSB, then build a fixed frequency SSB source and mix this with a standard sig-gen.The alternative is plating with IQ modulation, and all the major test equipment companies have IQ capable sig-gens.

author: GK
author_rank: Super Contributor
timestamp: March 19, 2014, 03:53:06 am
content: Quote from: KJDS on March 18, 2014, 09:15:38 amI almost suggested the same thing, but if a variable operating frequency is required over some significant range, filtering out the image (if required) becomes an issue.

author: G0HZU
author_rank: Super Contributor
timestamp: March 19, 2014, 11:21:26 pm
content: QuoteI don't really play much with old school SSB radios these days but in terms of getting accurate signal levels into the radio then as I said earlier I either use a single sig gen in cw mode, or combine two cw sig gens for a classic two tone SSB signal. Or I inject noise.The above methods are very simple and hard to beat. However, if you go down the alternative route(s) of trying to use a discrete modulator + mixer and filter and variable attenuator then it becomes harder to keep the total measurement uncertainty under control. You can do it this way but you need some pretty decent test gear if you want to prove you are still getting good level accuracy.However, a lot depends on what band you are testing. On HF it doesn't really matter too much when it comes to measuring the sensitivity of the radio because accuracy isn't really that important. But on VHF/UHF the uncertainty of measurement can soon become very significant with respect to the noise performance of the radio.If you really do want to use speech waveforms then I'd be tempted to just use the low level output from a low level stage in another radio via a suitable attenuator. I'm guessing that level accuracy isn't important here and it would be things like AGC performance and general clarity that would be the most important.I find the two sig gen approach to be the best in terms of fishing for problems in the receiver path. But a single tone is OK for looking at basic sensitivity and basic AGC tests etc. Being able to inject noise (especially gated noise) can be useful too because you can test out things like the noise blanker characteristics and it can be useful for sensitivity tests too

author: rjk5378
author_rank: Contributor
timestamp: March 24, 2014, 12:24:26 pm
content: Perhaps this may be of some help?http://www.elecraft.com/manual/2T-Gen_Manual_Rev_B.pdf