Ask Michael, KB9VBR: Does the size of the window screen (faraday cloth) ground network matter?
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- Опубликовано: 10 июл 2024
- Window screen or faraday cloth; size, shape, or length: Do these make a difference in the performance of the magic carpet, that is, the window screen or faraday cloth ground network for vertical antennas? Michael and Joe answer the most common questions received about the magic carpet.
The video that started it all, the Window Screen Ground Plane: • Window screen antenna ...
Faraday Cloth, the new magic carpet: • This is the new magic ...
Rothammel's Antenna book: rothammel.com/Rothammels-Ante...
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#Hamradio #AmateurRadio #POTA #ParksOnTheAir #PortableHamRadio #windowscreen #faradaycloth #groundscreen #magiccarpet #groundradials #groundnetwork #verticalantennna #askmeanything 
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When You have 1 counterpoise wire the take off angle will be lower and longer in the direction of the wire. As a truck driver I had a very long counterpoise (My Truck and Trailer) . In and empty lot in Missouri I had my trailer pointed east and made several contacts to the east coast and Europe but not to many to the west . Turned the truck around and was hitting west coast and Hawaii.
Yes, I have an ATAS 120 on a bonded Ram 2500 and have to maneuver to get my gain going the right direction.
Cool, I've been wondering about this very topic, thanks.
Very good tip from the book of antenna ... I had not bought any book about antennas, now is on its way 😉
Many thanks for sharing
Great job as usual Mike...got all my supplies at Hamcation for the 10 Mtr j pole...hope to build and get up this week...have a total shoulder replacement on the 26th so looking forward to alot of ham time while recovering..
Paul K1YOU
My vertical is in the back corner of my small suburban lot. I use two sheets of anodized aluminum screen at the base of the antenna, connected with jumper wires to the base of the antenna. They cost about $12 each delivered. Came from Amazon. For portable I put them in a PVC pipe, rolled up. I see good improvement in the vertical's performance. I am too cheap to buy Faraday cloth. My sheets are 36 x 84 inches. Held down with rocks.
8:15 Somehow, I got a bolt of square Faraday cloth when I bought mine!
I set up a vertical, last Field day and I used 4 rolls of the screen covering a 360 pattern. That set up on that day and conditions did very well. If I double the screen length it should make the lower bands more effective. Thanks and 73 Earnest K5EWM.
The most expensive faraday room I have seen is in Paris, at the labs of Professor Branly, who built a Faraday room out of solid copper sheets. The room is about the size of a two-car garage, with a ceiling about 20 feet up. Doors have copper gaskets. The room was built for experiments with crystal detectors, among other things. It must have cost a fortune in 1900.
Good video. I like to think of radials and ground screens forming a plate of a capacitor with the ground being the other plate. This capacitor has a reactance ( measured in ohms) that is inversely proportional to the capacitance ( measured in pF) and inversely proportional to the frequency. If this Xc value is low it makes a good low impedance connection with the ground. The major thing is to have the impedance low. This impedance can be purely resistive by having multiple ground rods or many long uninsulated radials or it can be purely a low reactance ( from the capacitor ) or it can be a combination of both. We are usually simply collecting return currents through the earth with radials or a screen. Above ground radials do the same thing but they actually form what amounts to the other half of the antenna. Think of it as the other half of the dipole or half of the antenna. The return currents must get back to the source some way or the antenna just will not work. How these return currents get there is hard to see and understand. Usually it is multiple ways not all of which are obvious. Like a mag mount on a car roof. That’s a capacitor and it is usually provides a low enough Xc ( impedance / reactance) so that it works well on higher frequencies but may not be a large enough capacitance on lower frequencies.
Most metals work as well as another but some are more durable, last longer and easier to work with than others.
😮I've used a roll of chicken wire and it worked well.
Yep, the type of material you use really doesn't matter. Window screen works well because it rolls up easy.
If elevating radials (theoretically) works better, would elevating a faraday cloth work better compared to flat on the ground?
Can confirm. I have been using the faraday cloth for a while now. When I look at my QSO’s they are very circular from GA. My cloth is a rectangle and I’ve laid it north/south and East/west just to see. The patterns of QSO’s are very similar, I can’t see a difference, both are a circle.
I've noticed the same. I haven't been able to influence any directivity with a single piece of cloth.
I use the Home Depot window screen and it works fine. My next experiment will be an aluminum foil turkey pan, filled with 6” of water for weight, clipped to the leads.
Way over my head, I do want to visit Joe’s shack: looks like a giant toy store 😲
THe faraday cloth rolls up to nothing and that matters, especially if you travel a lot or backpack. I use two faraday cloths on lower bands routinely, it makes a difference. One other weird thing I do is I have one attached to my ATAS-120A mount. It helps on higher bands even with a well bonded vehicle. Funny thing is, I used to pull it out and lay it over the top of the car. Now I just leave it inside the car. They work the same.
Hello, have you noticed any substantial differences between the mosquito net and the Faraday blanket with equal surface area? 73 paolo
The screen with a couple wood pieces works betten. The carpet is a pain to put down in the wind and you have to bring to pin the corners down.
I was out on Saturday and the wind was gusting to 30mph. i would never had been able to get the cloth laid out, but the screen stuck to the ground and never blew away.
i have an idea. two screens in a in a plus + layout.
How does the screen/cloth compare to a single elevated resonant radial?
That's a good question. I've been concentrating on ground mounted networks and hadn't considered elevated vs ground. I'll have to do some head to head comparisons on FT8 or WSPR and see what the difference is.
With the 44" x 108" cloth, I've noticed that on 20m I can easily get SWR under 1.1 and low reactance, but by the time I get to 10m I can't get it down much below 1.5. 108" is slightly more than 1/4 wave on 10m and slightly less on 12m, so might I actually have too much surface area for those bands?
I wonder if folding the cloth in half, or at least partially, would benefit the 10 meter band. You'd cover less surface area and presumably would be able to get a better match.
@@KB9VBRAntennas I was finally able to experiment and yes, folding it in half does improve SWR on the higher bands. I got the dip on 17 meters down to 1.1-1.2 and the lowest point on 15 through 10 was at 1.05. Reactance was still low and I was getting good reports back. 73 de KB9OFH
Is it the length or square footage that matters? I can put up 33 square feet in my area but not length like you'd have if you used window screen
It's surface area, not length that matters. So, an oddly shaped screen won't make a difference in performance.
The 25th edition of the ARRL Antenna Book is $69.95 or $79.95 depending upon edition and the The Rothammels Antenna Book is 59 Euros or about $64 dollars. The price of any of the books does not include shipping. I was going to buy the ARRL edition but after Joe's comments, I may go with Rothammels. But either way I will wait till the two of you do a video comparing them. :)
The Rothammel, which is here in Germany like the antenna bible, has a certain style. It is like a huge collection of knowledge from different people. There is like everything about antennas. Today I was looking for counterpoises and got like 57 different pages in the table of contents. What I mean, you will need time to find something in the Rothammel. So I thought about buying the ARRL Antenna Book. If it is anything like the ARRL Book on Radio communications, then it will be much tidier and easier to read. I talk about the german version of the rothammel, have no clue, how the englisch version is.
The 25th edition of the Antenna book is new and I don't have it in my library yet. I'll pick up a copy and do a comparison of the two.
On a side note, I looked at the receipt and with shipping and exchange rate, my copy of Rothammels cost $86.97 USD.
When you are doing POTA in the car, do you get your power from the cigarette lighter plug? If so, how many watts is it safe to run? Thanks!
I don't use the cigarette lighter to power my radios as they are current limited to 10 amps. They can also be noisier on the HF bands than a direct connection to the vehicle battery. My vehicle battery runs the dual band VHF/UHF mobile in the car but I always use an external battery for HF. The VHF/UHF has a direct connection to the battery to avoid the limitations of the cigarette lighter.
@@KB9VBRAntennas I figured as much, just wanted to ask. Never know what kind of trick you might learn. Thanks!
So if it works on top of snow, perhaps it could work while I'm out ice fishing. I wonder if the lakes depth would have an effect on signal performance? Or maybe, the ground plane negates that? If anyone has tried it on a frozen lake let me know how it went. I think a big wide open lake could be a great place to transmit from with a vertical that has a low takeoff angle. I'd love to hear what everyone thinks (maybe a winter field day on lake Michigan).
That's a good question and would be a great experiment.
Can you clarify as to the ground connection between the screen/carpet and the antenna base? I think I heard Mike once say it isn't necessary. Anyone have a definite answer to this?
I just put the antenna on the screen as it's great...
Paul. K1YOU
Any conducting path between the ground side of the antenna and the carpet will serve. E.g., in past videos Michael has set a WRC tripod on top of Faraday cloth and gotten a solid ground, but he's also used an alligator clip on window screen for insurance.
I use an improvised spike mount (3/8"-24 mirror mount + tent spike) stuck into the ground next to my cloth. I reinforced the edges with Faraday tape and put a lead on my spike mount which I clip to the cloth. VSWR is 1.1 or below with low reactance on 20m (CHA SS17 whip, no coil).
73 de KB9OFH
You need a good connection, or continuity, from the ground side of the antenna and the cloth/screen. If your tripod or support is all metal, setting it on top of the cloth is sufficient for continuity. If it is plastic or you don't ahve continuity to the ground side, then jumpers will be required to make a connection.
Thanks, all!
Does chicken wire fence vs. window screen?
Material doesn't matter as much as surface area covered.
so is that book the King Charles version?
Hi Mike, thanks for the POTA contact on Saturday. 73 gd DX - George AH6UN / OE4JHW
Glad to get you in the log.