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two tone questions

I am confused over the "ideal" frequencies to use for a two tone test of a SSB transmitter. Art Collins' book states that using two tones with a 3 to

5 relationship will make it easier to identify intermod products and harmonics and in fact Collins used 3 and 5 KHz as the two tones. Modern SSB rigs only have about 2.7 to 3 KHZ audio passbands so 3 and 5 are not much help. I see articles using evrything from 400 & 1900 Hz to 1.1 & 2.2 KHz.. Is there a "best" pair for testing modern rigs, or is this all a lot of hype and any two tones inside the passband wil work?

Ron H.

Reply to
Ron H
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You don't have to use 3 and 5 kHz to have the same ratio - you could use 1.5 and 2.5 kHz, or 900 Hz and 1.5 kHz.

I think the "magic" of the 3:5 ratio is that 2nd-order intermod comes out at 2 and 8, and neither 2 nor 8 are harmonics of the 3 and 5. This helps you test for intermod independently of nonlinearities in the audio chain. 1.1&2.2 doesn't have this, but 400&1900 does.

The small-integer ratios help a lot with identifying frequencies on Lissajous figures (something that 400&1900 doesn't have for appropriate values of "small integers".) This doesn't seem particularly relevant to intermod testing but it may determine what standard fixed freqs you have at your test stations.

For broadcast-quality (AM or FM radio) audio they tend to use one very low frequency (like 60Hz) and one very high frequency (like 7kHz) in intermod measurements. I don't think these are relevant to SSB comms because they both fall way outside the passband. I seem to recall that for broadcast intermod measurements they are also interested in higher-than-2nd-order intermod (so they are looking for F2-2F1 and F2+2F1 as well) and for SSB voice comms we usually aren't that picky.

Tim.

Reply to
Tim Shoppa

And as always the intermodulation test signal products should be in the passband.

--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.  
--Schiller
Reply to
Joseph2k

Is that necessarily true? I mean, intermod made in the drivers or finals have no chance of being filtered out by your sideband filters. It ends up splattering all over the band, and while that's not "your" passband it is everybody else's!

Tim.

Reply to
Tim Shoppa

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