I was on 40m #JS8Call when OH8STN sent Heartbeat message from few kilometers away. It was overwhelming my RX and I managed to catch a screenshot.
His message was sent on frequency 889Hz, but we can also see signal harmonic on 1778Hz (2 * 889Hz) and 2667Hz (3 * 889Hz).
Also notice how the width doubles on 2nd harmonic (1778Hz) and triples on 3rd harmonic (2667Hz).
Maybe this doesn't have any other point, but to show how harmonics look like on waterfall.
Sorry, there's error between screenshot and numbers!
I have wrong base frequency here. Screenshot doesn't match the numbers. Clearly in screenshot it's not 889Hz, but something between 900-1000Hz.
My numbers are wrong due to earlier screenshot I took where the base frequency was 889Hz. Sorry about this!
However, the math should still work (just change numbers) and waterfall screenshot shows how it looks.
@M0YNG Indeed! It took me a while to understand what's happening. What I don't know if why is it happening.
From these little things we can learn and build our knowledge.
@M0YNG That looks fine. A better metric for too much power would be seeing very lopsided reports like sent -23 received +10 😂. Sometimes band conditions are great and even a tin whistle signal gets a great report.
How does the signalink not reduce the tx power? Of course it does. I always have a power meter running btwn transceiver and antenna when I am in digi mode. And I really hate fiddeling with the tiny nobs of the signalink. But I always reduce the output power to 10-35W, depending on the mode. I never touch the radio.
As you all know, digi doesn't feel like the 'real thing' to me when being on the radio but being a witness of the arms race of power increase feels ridiculous. To get a rare DXpedition station, people are ready to run 1KW in FT8.
@M0YNG @es0mhi @oh8hub You really need watch the ALC and make sure you are not driving it into limiting. Also research your specific rig. Elecraft had a different approach to the ALC metering than most with their K3. A cross-needle SWR bridge between rig and antenna could serve the dual purpose of keeping an eye on your SWR as well as showing the forward power.
Concerning observation 2: of course you know this very well but the general naivity in these matters may make it worth repeating: doubling the power will result in a signal increase of 3dB. If your antenna is poor or the propagation is problematic that will make no real difference. (And the reason ur not heard doesn't have to be ur signal at all: I get the impression, that digi modes are often run by people with horrible antennas and a terrible noise floor ;-)
obs. 1: sounds as if you can see how much amps it is drawing - now there should be noticeable difference there.
@W8HF Yeah, I'm using a cross needle SWR/PWR meter.
I had my rig's RF gain up. Lowering gain down removed the harmonics. So this phenomenon was purely on my RX side.
This is a screenshot of me lowering the RF gain in middle of heartbeat transmission. See how the harmonics just disappear while original signal still continues on it's frequency.
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