[Amps] Checking for IMD

[Gary Schafer]

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Tom W8JI
> Sent: Monday, August 14, 2006 11:34 AM
> To: amps at contesting.com
> Subject: Re: [Amps] Checking for IMD
> 
> > Switching side bands IS the same as tuning your receiver
> > the width of your
> > filter.
> 
> No. It is not the same.
> 
> The filter is offset from the carrier in both the
> transmitter and the receiver, and you will miss the
> close-spaced high audio frequency tones that would be in the
> clear if you tuned.
> 
>  >If you have a 3 KHz wide filter and listening to the upper
> side band
> > and you tune down 3 KHz with the tuning dial, you have
> > moved the receiver
> > pass band the same amount as when you switch to lower side
> > band and leave
> > the receiver dial alone.
> 
> No it isn't. The transmitter has a 300Hz or some filter
> offset from the carrier.
> 
> Assuming the receiver has the same, the error is 2X the
> offset. This does not occur if you tuned down the filter
> bandwidth and stayed on the same sideband.
> 
> 73 Tom

Think about that again. If you are listening to upper side band with a 3 KHz
filter and you tune down 3 KHz in frequency with the dial you have moved the
band pass the same amount lower in frequency as you would if you switched
side bands with the side band switch. The only difference is that the
carrier will be on the other side of the filter.

Yes the transmitter has an offset of 300 Hz or so and we will be receiving a
slightly different set of IM frequencies due to the offset but with voice as
the signal source it doesn't matter. If we were using two fixed tones for
modulation of the transmitter then yes it would matter.

73
Gary  K4FMX