HF Propagation can not be so bad! ;-)

I am currently testing a remake of the “Old School SSB TRX” modified by adding a Dual-DDS-VFO to enhance frequency accuracy and stability.  The rig is completed and a description will follow within the next weeks. But another finding is notable.

Currently I am using WEBSDR sites to monitor my own signal from time to time. On sdr.hu you can find a large number of WEBSDR sites from all over the world. Most of them are somehow insensitive because they seem to use suboptimal antennas. M0RZF appears to be different.

I first had an initial test monitoring the two-tone signal for some seconds on 14.200 MHz with the WEBSDR and the transceiver connected to a half wave dipole antenna.

After some seconds I switched the transmitter off, disconnected the antenna and connected a BNC cable terminated by a 50Ω dummy load. I watched the signal on the scope and the spectrum analyzer and did some measurements. Output power was about 20 watts PEP.

When adjusting the transmitter I, by accident, got the PC monitor from the corner of the eye with the SDR still on it. I was pretty surprised when I noticed this figure:

SSB signal to dummyload received on UK WEBSDR (PWR 20 watts PEP)
SSB signal to dummyload received on UK WEBSDR (PWR 20 watts PEP)

Well, the antenna cable is on the desk about half a meter distant from the dummy load and it seems that there is enough stray energy coupled into the 50Ω-antenna-cable to produce a discernable signal over 1000 kilometers away. But nonetheless, pretty surprising.

Conclusion: Always be careful when testing your transmitters with a dummy load what you are about to  talk into the microphone! Use a two-tone test generator instead! 😉

Vy 73 de Peter (DK7IH)

2 Replies to “HF Propagation can not be so bad! ;-)”

  1. Even a small amount of RF is a sneaky thing, it gets in and gets around. And out to the ether. A few months ago I was on SOTA summit Mt Dandenong VK3/VC-025. I made 4 or 5 CW contacts but wondered why the reports were so low. The next week a few regular chasers complained that they couldn’t hear me. On the bench I found the IRF510 had blown and the BFU590 driver was delivering 15mW to the dummy load. An unintended QPRp activation.

    The KiwiSDRs on SDR.hu have been absolutely invaluable for remote monitoring my transmitters. I also use them to get a better copy on interstate stations on 160m AM in the evenings. They are a great development.

    Hope to read of your Old School SSB Trx soon. Paul VK3HN.

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