The Baked Potato Radial

I recently watched Michael KB9VBR's YouTube video on using a Faraday cloth as a radial network. He has been using a window screen for this purpose, but found that a Faraday cloth has the same performance with less weight.

I was almost about to click "Buy It Now" on the Faraday cloth when I had a thought, "Would a Mylar blanket work the same way as the Faraday cloth or window screen?". So at lunch I went off the hardware store and grabbed a 36" x 84" window screen and some hardware to clip it to my mag mount. I already had a 52" x 84" Mylar blanket in my bag, so I didn't have to buy one of those.

I made 3 different radial networks:

  1. 4–17' speaker wire radials
  2. A 36" x 84" window screen connected via an alligator clip
  3. A 52" x 84" Mylar blanket connected via an alligator clip

My test methodology is to extend the 17' whip 100% and do the following:

  1. Record the SWR curve for 20m with NanoVNASaver
  2. Transmit 5W of WSPR for 10 minutes and record who hears me

I set up each radial in my backyard and recorded the results.

Speaker Wire Radials

So this was my "control". It is 4 17' speaker wires. It is probably the bare minimum as far as the number of radial wires for a vertical antenna. Even with so few radials, the SWR was OK. I guess my soil has good ground conductivity.

You'll notice that the curve slopes downward on the left, this means that I could make the SWR even better by shortening the 17' whip. To get an idea of how low it could go, I expanded the sweep a little bit. I could get it as low as 1.3 with some tweaks. Would I bother? Maybe not. If the SWR is <2, I let the auto-tuner take care of the rest.
Here is how many stations heard me after 10m of transmitting 5w WSPR at 100% of the time

My FT-991A tuned the antenna just fine and reported about 1.1 SWR
The speaker wire radials are pretty nice. The SWR is good, and they're pretty easy to set up. The downside is that their footprint is pretty large. I need a 17' x 17' patch of ground to fit the radials. They literally filled my puny yard corner to corner.

The "Magic Carpet"

Michael KB9VBR introduced the magic carpet to the world. It is a 36"x84" patch of window screen. I wanted to try out the magic carpet to see if the Mylar blanket was better or worse than the window screen.

The footprint of the window screen is much smaller. I can see the appeal of the magic carpet in a park where space is limited.

You'll notice that it does worse than 4 wire radials, but still less than 2 SWR across the 20m band, so I say that's good enough.
The number of stations that heard me on WSPR was far fewer. The stations in the states looks about the same, but I didn't get as many in Europe. I don't know why this is. You'll see next that I should have had similar results to the speaker wires.
The FT-991A had no trouble tuning up the antenna with the window screen.

The "Baked Potato"

Here's what the article is all about. What I've lovingly started calling the "baked potato" radial. You can see in this picture why I have been calling it the "baked potato". I would also accept burrito radial.

The Mylar is a little fiddly. It is very light. I had to weight it down to keep it from blowing around. It is also pretty loud. It sounds like a thousand grandmas unwrapping hard candies at the same time. This is not for covert operations.

The Mylar blanket is very thin. I worry that my alligator clip will eventually tear it. In fact, the blanket in the photo above is my second blanket because I accidentally tore the first blanket. If you go this route, buy two. They are cheap and light enough to have some redundancy.

I won't lie. The SWR is rough. It crosses over the 2.0 SWR threshold I use as "good enough". In practice, it doesn't seem to perform much worse than the magic carpet. The SWR is still less than three which means the FT-991A's ATU will tune it just fine; 1.1 like the others.
I expected similar WSPR results to the window screen. Strangely, the stations that heard me are similar in quantity as the speaker wire. I guess maybe the propagation gods were against me during the magic carpet WSPR run.

Size and Weight comparisons.

Where the blanket shines is in weight and size. This is a quick size comparison. If I tried harder, I could have compacted the blanket more, but I folded it up in a hurry. If you really want to save space and weight, there's no contest with the blanket.

The weight comparison is pretty significant:

  1. Window Screen: 310g
  2. Speaker Wires: 169g
  3. Mylar Blanket: 46g

I bet you could use a Mylar blanket as part of an ultralight radio kit if you wanted to.

POTA Experience

This past weekend I took the radio out to US-7730, McKee-Breshers Wildlife Management Area. The parks service plants fields of sunflowers for wildlife to eat. This weekend, they were in peak bloom. They were a sight to behold.
After looking at the flowers, I took my radio down to the bank of the Potomac river and set up the 17' whip and Mylar blanket radial.

I made 32 contacts in 28 minutes @ 80W. Albeit, this was the best possible conditions for the blanket. It was on the bank of a river, on muddy clay, good solar weather, and "supports your parks" POTA weekend.

It was a hot one, both in terms of temperature and hunters. This activation was the first time I had back to back pile ups. After about an hour of setup and responding to stations, I was spent.

I wish I could have compared the performance of the Mylar blanket to the wire radials, but I didn't have it in me. To be honest, where I was set up, I doubt I had 17 square feet to lay out the wire radials.

Conclusion

After trying out the window screen. I'll have to say, I'm not a fan. It is large, hard to store, and the edges fray easily. A number of times the edges poked my hand. It is very likely after I'm done using it as a baseline, I will throw the window screen in the trash.

The downside is that the blanket is that it is fragile. While the Faraday cloth is more expensive, if I keep tearing the Mylar blankets, the lifetime cost of the blankets will likely exceed the cost of one Faraday cloth.

All in all, I am actually surprised the Mylar blanket worked as well as it did. I went into this experiment expected it to fail miserably. Furthermore, I think if I could find a larger blanket or use two, the SWR might go lower.

If you want to save space, weight, or money, try using a Mylar blanket as a magic carpet. If you try it, hit me up at @k3fnb@mastodon.radio, and let me know how it worked out for you. I'd love to find out what other people's experience with it has been.