[AMPS] Splatter and ALC

[Ian White, G3SEK]

W8JI quoted:
>
>"How's my audio?"
>
> "It sounds great."
>
> "OK thanks, then I must not be splattering."

Yecchhh.... it's the same the whole world over!


The only way to check whether you're splattering across the band is to
ask another ham to go and listen.

Find a totally quiet band, and a local station whose operator whose
operator you can trust, and whose receiver you can trust to handle your
strong signal. Then ask him/her to tune across your signal and at least
20kHz either side, while you count slowly up to 20 and back down again. 

(Don't ask somebody to tune across your signal, and then continue
talking as normal - they'll politely stay on the frequency in case they
miss something. If you count up and down, it tells them how long you
expect it to take, and they know they won't miss anything important.)

When you're both back on the same frequency, ask them to tell you:

1. How many kHz does it take for your signal to drop into the noise, on
either side of your main signal?

2. Further out, are there any transient peaks of splatter? How high, how
far out, and how often?


Then change over and return the favor. 

This isn't a laboratory-standard measurement, but it does have some real
advantages over lab techniques:

* Our HF receivers often have more dynamic range than our spectrum
analysers (which tend to be older models if we have one at all). 
You can hear low-level IMD from a spreading signal, and also transient
IMD - splatter - that the analyser would never show.

* You can check for receiver overload by comparing the width of another
signal of equal or greater strength.

* The voice test exercises the whole transmitter: the exciter, the
amplifier and its power supplies. A two-tone lab test doesn't check for
any transient effects, which are often the most annoying.

* It gives a direct answer to the key question: am I causing
interference to my neighbors on the air?


73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)

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