Simplest is to talk into the mike and use a second receiver and flip to the
opposite side band and compare levels. An attenuator of known calibration
ahead of the second receiver will get you in the ball park for overall IMD.
If using two tones, use the second receiver as your spectrum analyzer. Tune
it to where the 3rd and 5th order frequencies should fall using the cw
filter. That will separate the IM products from the fundamentals. Then read
the difference in levels with the calibrated attenuator. This will give you
just as good readings as a spectrum analyzer will.
You must take care to not overload the receiver and make sure the signal
only arrives to the receiver via the attenuator and not stray pickup.
It is best to check the attenuation of the attenuator / receiver setup at
levels that you will be measuring.
An HP selective level meter can be used to do the same thing. They can be
picked up for around $150.00. Works very well. It gives you a direct readout
in db of level difference.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Bill Turner
> Sent: Friday, August 11, 2006 9:24 AM
> To: amps@contesting.com
> Subject: [Amps] Checking for IMD
>
> Is there a simple procedure one can use for checking the IMD of an
> amplifier? Frankly, it's something I have never tested myself, instead
> just keeping the amp tuned correctly and underdriving when using SSB.
> I've never gotten any complaints of splatter so I think it's under
> control. Since I do mostly RTTY and some CW it has not been an issue
> but I would like to be able to check it.
>
> Any recommended reading on the issue?
>
> Bill, W6WRT
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