[Elecraft] An AGC story

[Geoffrey Mackenzie-Kennedy]

Hi John,

The NPR test is, I agree, certainly a very useful method to expose IMD
problems, but I think that when used as a *diagnostic* tool the requirements
placed on the notch filter's bandwidth limits this method's versatility -
unless one is prepared to build a set of band reject filters (probably
crystal) that may be required, whose IMD contribution is much less that that
of the receiver, device or sub-system being tested.

To obtain low phase noise from my IMD test arrangement I have been using low
noise crystal oscillators followed by +40dbm output amplifiers, which is I
admit a cumbersome approach, but it did provide useful results until I
damaged the equipment while measuring the IMD generated by some types of RF
transformer - a sad story!

If Santa gave me a K3 I could stop speculating about its multi signal
performance :-)

73,
Geoff
GM4ESD


"juergen" <plebian99 at yahoo.com> wrote on Saturday, December 11, 2010, at
6:18 PM:

> Hi Geoff

> The noise power ratio test(NPR) might show more clearly any mixer IMD
> problems. The NPR test might also better characterize any roofing filter 
> IMD
> as well.

> The noise power ratio test  better characterizes dynamic receiver
> performance. The NPR test  also does not require expensive low phase noise
> signal generators.

> 73
> John