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Author Topic: Two Tone Tests  (Read 2177 times)
N6PAA
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« on: October 09, 2012, 12:41:10 AM »

Good evening all. The Precise RF Co. has a model TTG1 two tone audio generator for a steep asking price.  My question: Other than trying to build my own, are there other sources with a better price break for a 2 tone test generator? This of course is to be used to check transmitter linearity etc. Thanks, Ron
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G8JNJ
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« Reply #1 on: October 09, 2012, 01:06:58 AM »

Hi,

If you use a PC & digital modes You may already have all you need for a 2 tone generator !

I got rid of all my old clunky audio test gear some time ago. I now just use some freeware and my PC & Soundcard.

All of the following include tone generators and spectrum analysers.

Sound Card Oscilloscope - Easy to use and very versatile - will teach you a lot about audio !

http://www.zeitnitz.de/Christian/scope_en

T Cube - even easier to use but slightly less versatile

http://www.weaksignals.com/

Spectrum Lab -Very versatile but takes some getting used to

http://www.qsl.net/dl4yhf/spectra1.html

If you have an RF generator and build a simple mixer you can also perform simple RF measurements.

http://www.astromag.co.uk/ssa/

http://koti.netplaza.fi/~jonverro/sb_netm.htm

Regards,

Martin - G8JNJ

www.g8jnj.webs.com

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N6PAA
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« Reply #2 on: October 09, 2012, 01:16:42 AM »

Thanks for the suggestions Martin. Elecraft has a mini module kit "2-Tone Test Generator" model 2T-gen. Looks like a good piece of hardware coming from Elecraft. Thanks again, Ron
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G3RZP
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« Reply #3 on: October 09, 2012, 03:33:49 AM »

Getting the IMD way (60dB or better) down can be a problem with most any generator. I've done it with conventional generators by using a telephone type hybrid.
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W8JI
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« Reply #4 on: October 09, 2012, 04:52:14 AM »

Good evening all. The Precise RF Co. has a model TTG1 two tone audio generator for a steep asking price.  My question: Other than trying to build my own, are there other sources with a better price break for a 2 tone test generator? This of course is to be used to check transmitter linearity etc. Thanks, Ron

Many people think any way we generate a two-tone results in a good test, and even that a good two-tone test means a system has good bandwidth. A two-tone test is far better than no test, but does not check overshoot or dynamic regulation. It only tests RF dynamics at the tone spacing. For example if tone spacing is 1 kHz,  a 600 Hz and 1.6 kHz audio tone, the IF and RF stages, ALC, and power supplies are all tested at a 1 kHz load change rate.

That, of course, is nothing like speech. Of course it is much better than no test, but it really doesn't tell us we don't have a problem. It only tells us if could be clean, not if it is clean, but that can still be worthwhile compared to nothing.

The problem is always obtaining a signifcantly cleaner two-tone signal than the system beyond the generator, but fortunately most radios and amplifiers are not especially pure.

I use two or three good audio generators, each through a very high attenuation pad, as an audio tone generator.
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G8JNJ
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« Reply #5 on: October 09, 2012, 09:42:03 AM »

I agree with Tom.

Two tones don't tell the whole story - especially when ALC (and DSP processing) comes into play. Some sort of dynamic test signal is really required.

However even a soundcard based test is normally of sufficiently low distortion. That any contribution from the source will still be a long way down on the typically -30dBc intermod products, produced by an average amateur grade TX.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com



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