Power output when operating CW from the front key jack?

K1FSY
Posts: 13
Joined: Mon Mar 27, 2023 1:30 pm

Power output when operating CW from the front key jack?

#1

Unread post by K1FSY »

Hello! I'm working on my CW and I have a hardware keyer (winkeyer) for computer control and paddle control. I have noticed that when using it on the PTT/KEY jack on the front of the Hermes Lite that it always runs full power output. I was able to lower the power very insignificantly with the "OP Power" slider on the radio panel, and the drive slider on the TX panel appears to have no effect. Is this expected behavior or am I missing something? I typically run at max OP and around 60% drive, so 100% drive is a little much into the amplifier. I am using the low power output on the HL2. I can turn down the TX gain on the transverter to compensate but I wanted to check if I am missing something first.

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Simon G4ELI
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Re: Power output when operating CW from the front key jack?

#2

Unread post by Simon G4ELI »

Sorry, at the moment I don't know the answer.
Simon Brown :shock:
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Max
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Re: Power output when operating CW from the front key jack?

#3

Unread post by Max »

K1FSY wrote: Mon Nov 13, 2023 1:12 pm Hello! I'm working on my CW and I have a hardware keyer (winkeyer) for computer control and paddle control. I have noticed that when using it on the PTT/KEY jack on the front of the Hermes Lite that it always runs full power output. I was able to lower the power very insignificantly with the "OP Power" slider on the radio panel, and the drive slider on the TX panel appears to have no effect. Is this expected behavior or am I missing something? I typically run at max OP and around 60% drive, so 100% drive is a little much into the amplifier. I am using the low power output on the HL2. I can turn down the TX gain on the transverter to compensate but I wanted to check if I am missing something first.
I think you will find this is expected behaviour.

The key is to understand what the two sliders do (I hope have this right Simon):

Drive on the TX DSP panel (not enabled or relevant in pure HL2 "CW mode") changes the amount of audio drive sent to the HL2 via IQ output.
OP Power (in the radio panel) changes the power range adjustment directly on the AD9866 chip in the HL2. This is of limited range (see below)

So in pure HL2 CW mode understanding is that the IQ inside the AD9866 is keyed "full on" and so the only gain adjustment you have is the gain setting of the chip via OP Power. This only operates over a relatively small range of 7.5dB. So that's the maximum gain control you have in CW mode at RF1. Steve Haynal has stated this on quite a few occasions over on the HL2 Group:

https://groups.google.com/g/hermes-lite ... kT9WhrAgAJ

You can confirm this by watching the output of the HL2 with the PA enabled and on the ANT (RF2) output. Short the CW/keyer input pin (can be done by wrapping silver paper over the 3.5mm audio jack plug) and vary the power out purely by use of the OP Power slider in the radio panel. You will see the range approximates to that 7.5dB. I don't have a lab accurate wattmeter but on 40m I see variation achievable using solely the OP Power control of about 1W to about 4W so sort of nearish to 7.5dB. It does seem to vary a bit depending on band. I put that down to the PA and all additional circuitry which of course is not seen at the low power output. I have nothing to measure power out at the very low levels of RF1 but my guess is it's pretty much bang on 7.5dB.

I got around it by turning down (or is it up!) the input drive attenuator inside my transverter.

Hope it helps.

73

Max

K1FSY
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Joined: Mon Mar 27, 2023 1:30 pm

Re: Power output when operating CW from the front key jack?

#4

Unread post by K1FSY »

Thanks for the detailed reply Max, this makes sense. I'll probably re-adjust the input gain on the transverter to compensate as you have.

Max
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Joined: Thu Aug 13, 2020 9:47 am

Re: Power output when operating CW from the front key jack?

#5

Unread post by Max »

K1FSY wrote: Wed Nov 15, 2023 12:14 pm Thanks for the detailed reply Max, this makes sense. I'll probably re-adjust the input gain on the transverter to compensate as you have.
Yes, for pure HL2 CW mode I think it's the only way (or use an external variable attenuator). I guess this is the correct thing to do anyway because it also calibrates the maximum permissible input power to the transverter if full drive is set on SSB too, so it's not a bad thing.

Ideally I guess it would be nice to have finer control of the output power in true CW mode, but that's just a Hermes Lite "thing" for this mode. Other option (no doubt you have thought of it) is to operate CW as SSB mode via audio tone input to TX DSP (create some custom RX filters in the SSB mode). It's a bit messy though I think. I believe it's a common solution for SDRs that have no native CW mode (like Pluto I think?)

73

Max

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