And the SDR radio and software now makes this possible. Have to say however you do this by SDR or analyzer that’s one clean amp you got there for that power level.
Hi Ray,
Thanks.
I'm using an HPSDR radio for spec display. These are semi-kit boards using a Mercury and Penny to produce a transmitter/ receiver combo that covers 160 - 6M. It uses Flex software, so has the same spectrum analyzer layout. I have it in the "duplex" mode so that I can sample an external signal and feed it into the receiver while transmitting. Most SDR's (Flex) are set up to monitor their own internal, low level signal, which always looks perfect... :-) Using a second Flex RX or a duplex option is required to see the high level final TX signal.
Later, I may use the low level signal from the HPSDR to drive this new amplifer chain that I've built up and have been testing.
The HPSDR spectrum display noise floor is quite deep when running 100 watts or so, but when up at 1500 watts, I can see some noise coming in at the floor. I think it is standard leakage thru coax, etc. It doesn't hurt the readings I am interested in since -70 dB is plenty of dynamic range.
The good thing is if the IMD is poor, it certainly shows up as it did in pic #1 of the barefoot FT-1000D ricebox. I used to think the 1000D was a pretty clean radio when running at reduced power, but it's no different than the average ricebox. The technology is available to produce riceboxes that are -40dB 3rd and much higher, but there's maybe one or two available that cost over $6K. I don't understand it.
As you said, these software spectrum analyzers are the best tool we've had as hams in a long time. I appreciate it and it gets a lot of use, now that the test set up is reliable.
I plan to run some IMD tests on my 24 pill class E AM rig soon. That should be very interesting to see. Stay tuned.
T