DX on a dummy load?

Foundations of Amateur Radio

Recently I made a joke about operating your station with a dummy load in response to John VA3KOT operating their station with the craziest antenna they ever used.

It got me thinking about the ubiquitous "dummy load" as an antenna.

Since becoming licensed I've spoken with several amateurs who tell a similar story, one comes to mind immediately, Lance VK6LR, now SK, who told me that they managed an unexpected 2m contact with another station using a dummy load, across the city. There's various versions of this doing the rounds, incandescent light bulbs used as both dummy load and antenna, coiled up roll of coax, everyone has a story to tell.

Having spent several years proving that you can in fact use 10 mW and be heard on the other side of the planet, 13,945 km away, it tickled my fancy to think about what would happen if I replaced my antenna with a dummy load on purpose, as a test.

For the past two or so months my WSPR beacon has been transmitting every ten minutes on the 15m band. It was heard 3,493 km away. Interestingly, even in that short amount of time, the radiation pattern of my antenna as seen on the "wspr.live" website shows a similar outline to the 10m transmissions I've been doing since late 2021.

The number of total spots wasn't nearly as significant. I added a local receiver to my shack, just to prove that I was in fact transmitting, but there were plenty of days without a single external report, this in contrast with my 10m experiment where most days I had at least one or more reports from outside my shack, most of them outside my state.

In other words, not every band gets the same kind of report. My license restricts me to the 80m, 40m, 15m, 10m, 2m and 70cm bands. The two antennas I've used so far are essentially limited to a single band, unless I start tuning it every time I change bands.

As you might recall, I purchased a Hustler 6BTV antenna several years ago. Unfortunately, it's still sitting in the box. Climbing on my roof has not been an option for several years, but its time will come. The purpose of getting that antenna was specifically so I could use WSPR across multiple bands and see how propagation was in my shack in real-time without needing to rely on external forecasts or predictions.

Switching to a dummy load has several benefits and impacts.

First of all, it's not something I've seen anyone do. Then there's the idea of band hopping without needing to re-tune. The idea of radiating into something that's not supposed to radiate, is something that makes me smile.

Given that each band has a different level of propagation, which ones should I choose? I could pick all the ones I'm licensed for, but that would leave out the WARC bands and the ever popular 20m band.

What if I ignored convention and transmitted on all bands supported by my WSPR transmitter? Remember, I'm transmitting into a dummy load. By all accounts this should not radiate. It's taken as gospel by the amateur community that it doesn't.

So, using a dummy load, one that's rated at 15 Watts between DC and 150 MHz, feeding it with 200 mW, or 23 dBm, my WSPR transmitter is currently merrily pinging away across 80m, 40m, 30m, 20m, 17m, 15m, 12m and 10m.

If all goes to plan, nobody will ever hear this.

That said, I can hear the uproar from here.

What's the point? You're illegally transmitting on bands you're not licensed for. I'll report you to the regulator.

Here's the point.

The community and the regulator both state that the dummy load is the approved method for testing equipment. It's implied that the equipment will be happy and there will be no radiation. I'm testing and monitoring that assumption.

I'm using all bands because if conventional wisdom is right, nobody will hear this. On the other hand, if conventional wisdom is wrong, there will be reports from bands where there are many people monitoring.

I'll note a couple of other things.

There's a patch lead between the WSPR transmitter and the dummy load. It's about 200 mm long. It's the shortest one I have. It was terminated at the factory and connects the SMA output of the WSPR transmitter to the SO-239 on the dummy load. Theoretically it might radiate. Perhaps this is where other transmissions into a dummy load emanate from, perhaps not.

I discussed the idea of measuring the emissions from a dummy load with a fellow amateur versed in testing much more sensitive equipment. We were not able to come up with a way that would be simple to do by any amateur. If you have ideas, feel free to share.

I'm likely going to cop flack from those who think I'm doing something illegal. You cannot have it both ways. Either I'm transmitting legally or a dummy load isn't a suitable testing tool. Unless instructed by the regulator to cease, I'm confident that I'm operating precisely within the obligations and requirements of my license which encourages me to test and monitor interference, which is literally what I'm doing.

One other point. Until now my WSPR transmitter has paused for eight minutes between transmissions, transmitting once every ten minutes, or six times per hour. It was the default as I recall. I've changed that to transmitting every cycle on a different band. This means that every 16 minutes, the same band will get activated. It also means that because 16 minutes doesn't fit neatly into an hour, the band will move over time, which I think is a good thing. The frequency hopping appears to be round robin, so no grey-line changes, but feel free to correct me.

I don't know what this will do to the transmitter and if it will sustain this. I haven't asked Harry SM7PNV, but if it cooks itself, I'm sure that I can order a new one and mark it down as a lesson learnt.

So, have at it. Point your receiver at VK6 and see what you can hear. I expect to keep this running for a year and see what we learn.

I'm Onno VK6FLAB