Re: [Amps] Checking for IMD

["Tom W8JI" <w8ji@w8ji.com>]

> Ok... in my case I use the old TS-940 and I would have to 
> put a
> generator on it to see how it responded. The point was a 
> convenient
> point to compare the signals and your suggestion of 
> another point on the
> meter is well taken. The important point being that the 
> thing isn't in
> compression and you can compare levels there.

The important point is to know the flaws and keep the flaws 
of most receivers from being what we measure.

You'd have to look at the adjacent channel IM 
characteristics of the receiver and know its S meter 
behavior to know the best setting.

My only points are:

1.) It is not an average reading. It is something very near 
a peak power reading of the energy in the passband of the 
receiver filter.

2.) You have the make sure the receiver is far enough away 
in frequency so receiver filter blow through and filter 
skirts aren't an issue.

3.) You have to make sure the measurement level of the 
"splatter" is low enough on the meter that receiver IM isn't 
an issue.

4.) You have to know something about the S meter behavior. 
You don't want it to be in compression.

5.) If it's an "in the shack reading", you'd have to be VERY 
sure you measure all signal from a line tap and none from 
direct or power supply pickup.

6.) If it's an off-the-air reading you'd have to be sure you 
are reading the undesired signal and not noise or other 
signals. This would severely limit the ability to test a "no 
amp/amp" situation.

Other than that it is probably good.

73 Tom 


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