How to measure IMD?
- 13/06/2013 12:11
I run a couple of Softrock SDR transceivers and have now connected my
30, 20 and 17 meter one to my old Collins 30L-1 valved linear which I
restored a while back. It now gives about 5 to 8 watts. (WOW! :)) I
would like to see what the IMD looks like though, less than one watt
with a bit of IMD isn't going to worry many people, but if I up the
power I feel obliged to do my best to check the signal is as clean as
I can make it. I have a spectrum analyser, but I am not very good with
it yet as I worry about blowing it up. I am becoming a bit more
confident since getting a pair of DC blocks and some step and fixed
attenuators. I also have a biggish 100 watt 30dB attenuator and an
adjustable RF coupler. There are software programmes to inject a two
tone audio frequency into the SDR transceiver, I think? I believe this
is all I might need? So what I am short of is clear instruction as to
what to do and how to interpret the results. I believe just looking at
the signal on my `scope can be misleading as it may not show IMD well,
or at all.
I looked on You Tube and Googled, but found nothing of great use. Can
anyone assist please, either here, or by pointing me to some other
Chris Wilson. 2E0ILY
- 'cause IMD, as measured using the ARRL protocol, is specified with reference to PEP, which is accepted to be 6 dB higher than the two tone level.
I would be interested to see the mil protocol and specification if you have it.
(AKA Warren Allgyer - 9V1TD)
--- In email@example.com, FRANCIS CARCIA <carcia@...> wrote:
> The ARRL spec is the 6dB gift method not the mil method. If you add 6dB to the two tone level why don't you add 6dB to the IP3 also since it is the result of the two tones. Splain that Lucy.
> I'm attending the school of hard knocks trying to modify a 1200 watt MRI board to HF. Fairly easy to make power but a different issue to get good IMD on all bands.
> Frank WA1GFZ