[Amps] Why hasn't solid state replaced tubes?

[Gary Schafer]

Ian White, G3SEK wrote:

> GW4FRX made some very useful tests using a borrowed analyser with a 
> digital peak hold facility. By continuing to sweep across the whole 
> signal for several minutes, holding the highest signal level found at 
> each frequency step, the analyser builds up a good statistical picture 
> of the overall bandwidth that the signal occupies.
> 
> The composite spectrum is composed of IMD products from all speech 
> frequencies, and it generally looks like a ragged triangle with the 
> higher-order IPs disappearing below the noise. The longer you sweep, the 
> better the statistics, and the smoother-edged the triangle becomes.
> 

Hi Ian,

The problem with peak hold analyses is that a particular peak only has 
to hit once and it becomes the same class of data as a frequency that is 
almost constantly present.
It will tell you all the possible frequency "hits" that occurred but may 
give a false impression as to problems.

Broadcast stations have different standards to adhere to than amateurs. 
A broadcast station must have a certain "frequency contour" that the 
signal conforms to. It must not transmit anything outside that contour. 
Sample and hold analyses is how that is measured.


Probably the simplest and most repeatable way to monitor inter mod is to 
just switch your receiver to the opposite side band. Im products are 
going to fall on the opposite side band as well as on the wanted side 
band. On the opposite side band you don't have the wanted signal 
components to interfere with hearing the IM products.

As most transmitters now days have decent side band suppression, 
anything that is not 40 to 50 db down on the other side is a good 
indication of IM performance. It also takes the guess work out of tuning 
and how far away you can be heard. (how strong how far away is always 
subjective)
By listening to the opposite side band signals can be quickly compared 
to others.
Yes filter type and quality will make some difference so it is not perfect.

73
Gary  K4FMX