Re: Open HPSDR Hermes (14 bit ADC, EP3C25) Transceiver Card

Conrad, PA5Y

Why so hostile? I am not trying to upset you. I made it perfectly clear that I was referring to the transverter port at 0dBm and that I only operate at 50MHz and above. I also said that the K3S PA was a disaster on 6m, it is and that is why I use the TS-890S. I also said that I cannot achieve these numbers on 50MHz but accept it because of the higher noise floor on 6m. My aim is to be a good radio neighbour and to try and get others to do the same. You are obviously one who cares about such things, so I think that we are on the same side here.  You did not bother to read my post because you have your own preconceptions. You just want agreement that PS on the ANAN-7000 is the cleanest possible signal available. I agree FWIW.


My measurements were on HF, 28MHz to be precise and appropriate for some potential users.


You made a statement that Class A amplifiers cannot be better than -40dBc 3rd orders, that is not correct. Analogue TV amplifiers are better than -50dBc and have been for years. They used to operate at 1kW or more. I just grabbed the first thing that I could find that was not heavily mathematical to show that class A amplifiers were not limited to the constraints you mentioned. A mini circuits datasheet seemed reasonable. It is harder to get good IMD at 950MHz.


I am not the only one who is going to use the Hermes with transverters, the thread was originally about Hermes. Simon said that it is better to start clean rather than use pure signal as a crutch. I agree.  The Hermes is a clean source.




Conrad PA5Y


From: <> On Behalf Of oldjackbob via
Sent: 25 February 2022 18:48
Subject: Re: [SDR-Radio] Open HPSDR Hermes (14 bit ADC, EP3C25) Transceiver Card


On Fri, Feb 25, 2022 at 08:16 AM, Conrad, PA5Y wrote:

Look here at figure 3a, this is a Class A RF amplifier with no pre-distortion running at 2W per tone. The IM3 is -51.48dBc, this is at 950 MHz.


Good grief! This entire topic of your claims of wildly spectacular IMD3 numbers for your K3S and 890S has nothing to do with tiny amounts of power at 950 MHZ! The radios we're discussing (and the 7300 and the ANANs) operate at HF, not gigahertz!

And we've always been talking clearly in terms of final PA stage IMD3 levels, not some measurements taken at a transverter jack.

Show me the measured IMD3 from your K3S or 890S at the output of the PA finals at any power level over 5 watts, at any frequency the finals are designed to operate at, and show me it's anywhere near -50dB. Go ahead, I'll wait...


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