#375
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- เผยแพร่เมื่อ 29 ต.ค. 2023
- Just a quick video to document my quick comparison of portable vertical antenna VSWR sweeps using my ground radials vs. a conductive fabric mat, often called a "magic carpet". Note that these results are specific to my antenna configuration, your results may vary. I kept "everything" constant/unchanged between the two configurations to get an apples-to-apples comparison.
- วิทยาศาสตร์และเทคโนโลยี
Appreciate this video, nice and short and to the point. A couple of points to consider: If the antenna is being tuned by way of an antenna tuner, or lengthening or shortening the whip, or adjusting a coil, then the SWR can be tuned out using these methods. Certainly different materials will produce different results. If one is using wires and are happy with them, then they should use them. However, I can see the Faraday cloth as a convenient method for the POTA activist to get a good ground mat that is easier to carry and deploy than wires. SWR is not all it's cracked up to be, however. The main objective is to get the power to the antenna, and that power to radiate efficiently. The mat helps it do the latter to reduce ground losses - the main objective of a ground system. Some folks confuse tuning radials on the ground (kind of a futile thing since they get detuned easily) vs tuning them elevated for a 1:1 match. I'm in Fl, and I tuned more than one vertical antenna using one elevated radial about 6 feet off the ground. Worked well. Ground conductivity being different all over the country (see the old 1950s map on the web showing the country with its ground conductivity #s), I can see my area of FL as being an 8. Setting up an antenna here compared to my old stomping grounds in the northeast (Rhode Island, where the # is 2) will required different approaches. Ground conductivity is a very important aspect to determining antenna efficiency. 73 de Scott W1AL
It's good to see other test results that confirm what I've found for the last six months. The ground screen, or magic carpet, works and it is a an effective alternative to laying out conventional radials. After dozens of portable activations and thousands of contacts, I'm convinced that I'm not losing any performance but gaining loads of convenience.
Hi Mike, glad you found my quick measurements insightful, and confirming what you've seen. Your video from about 6 months ago that showed virtually the same propagation results using WSPR reports confirms that too. My limited playing around with the carpet and shown me that for my typical activations, my radial deployment is more convenient for me. Several of the parks I go to don't have nice clear patches of ground to lay the carpet out (too much brush, rocks, trees, branches, etc.) - the radials give me more flexibility and I can deploy them in less than a minute. It was a good experiment though.
Thanks for the Magic carpet ride, Genie. 😊
This was a wonderful experiment!
I'd like to point out however that SWR is not the best way to confirm that the radiator is creating a stronger RF transmission. For that we need to measure with a FS meter at various points around the yard and plot them for both conditions (radials vs. magic carpet). This is akin to a "proof of performance" that broadcasters used to do annually. The SWR readings really should be ignored and replaced with a Smith chart so that the complex impedance can be shown and compared against the FS readings. The vertical radiator is going to have a very low radiation resistance due to its small size and I suspect that the improved SWR is due to INCREASED loss in the ground current in the radial field. If the vertical has 20 ohms of resistance and 30 ohms LOSS in the field, it will measure 50 ohms and have a good match. It will however have a terrible FS measurement. This is why FS needs to also be measured.
I can tell you that for an AM BCB tower, there are 1/4 wave radials that are placed every degree or so. But more important than the 360 radials is the BONDING of them together especially near the tower base to create an interconnected web. This is to reduce inductance and increase capacitance to the Earth below. Most likely this is what the magic carpet is doing, but should be used in conjunction with the radials and affixed to them at many points of contact, not just through one wire which will have inductance. Because the currents in the radials are maximum nearer the tower and much less out at the perimeter, the carpet helps to distribute them evenly and maximize capacity coupling to the ground below. A broadcast station is fixed to one frequency, but as a ham we are frequency agile so the radial field will generally never be at its best, unless it is adjusted for each band or is comprised of many different lengths where each is cut to 1/4 wave for each band that the antenna "system" is going to be used.
Just my $0.02 from past experience on the job.
Keep up the GREAT work. 73 OM
All *excellent* points. And yes, if my goal was to get the best radiation efficiency, that's the route to go. However, my goal here was to quickly assess whether the fabric would give my rig a better match, and if so, THEN go see how well it performs in the field during my portable operations. But, since it would require more fiddling to get a better return loss, it doesn't provide enough of an advantage over my simple radial system for my portable use where importance is placed on things like ease of setup over varied terrain, quick setup/teardown, and good-enough radiation performance. A few thousand POTA contacts tell me that my existing system is good enough even though it certainly isn't the most efficient. Thanks again for the great comments, and the cool insights into how commercial broadcast installations are setup (where every bit of efficiency matters because it means reaching more customers).
Your post has more detail than what I was going to put into my comment, but you hit all the high points. I believe radials are the way to go unless the cloth is rather large.
I can't erect my 12.4m multiband resonant vertical at my new apartment complex that I know of yet. At my old place, I used 32 radials of whatever length the remaining wire in the kit let me make. About 10+ feet, as I recall.
What I had been doing prior to obtaining that vertical while using a Chameleon Mil 2.0 with extension on a Hybrid base transformer/coil was making a set of 4 for each band 80-6, but I got 80 done and never did up the rest. I know that cutting to length is usually more for elevated radials, but mine were laid on the ground, at least in this configuration.
I love my WRC vertical, but the radials are just so inconvenient -- just ordered the faraday cloth, can't wait to add that to the arsenal.
A very interesting outcome. Thanks for posting and take care!
Great experiment. I was always told that the higher in frequency the more radials, or tighter mesh on a reflector. This kind of confirms that. The common practice would be for a single frequency vertical the radils would also be tuned to length just like the antenna, just like we do with a dipole, we trim from both ends. So we use practical length radials and tune the mismatch out at the antenna for our multi band antennas.
Wow! The results are not what I expected. Great video.
Thanks for the data, this is helpful to many of us who like numbers!
What I like about the cloth is people will see it and tend to avoid stepping on it. I’m still using the aluminum screen door. Cheaper. Hihi
Ok thanks for the video, I do alot of POTA, I have tried the faraday cloth compared to my ground radials,since watching this video, IMO.... IMO, the faraday cloth is working as good or better than the ground radials. The faraday cloth is far easier and convienient for me doing POTA, keeping in mind my outfit is setup for portable quick deployment,,, the faraday cloth has been a great improvement for my "PORTABLE" operation. thanks again for the great video, very well done Thank You, NS9T 73
Great demonstration!
I recently ordered some of this stuff.
It was called Faraday cloth. The plan is to use it in the shack to shield from rf getting into my computer.
Along with adding more ferrite where needed of course.
Great comparison. Thanks for sharing!
Very interesting and helpful, Thank You!
Thank You for sharing your results with us. 73
Try putting a single radial on each corner of the 'magic carpet' and stretch it out away from the antenna. I think that will solve the SWR problem on lower bands. BTW, I suspect the 'carpet' produces more field strength than the radials do 100 yards out from the vertical.
I was going to suggest that FS test
@@markherman7619naaa, the more area thats metal the better.
@@markherman7619 I have 120 feet of the cloth in two sections of 60 feet each, I cross them and they work really well, wires end up being more work but for low band I just add one wire to the end of one cloth. Very simple compared to just wire alone.
@@markherman7619, it's all about getting the optimum result with the minimum of effort. Walking out radials as you spread out the corners of the blanket is essentially no effort, yet I'm thinking you will gain the best results of both.
Great info, thank you
Very interesting results!
Take the tripos caps off and repeat.
I actually ran that experiment after the filming was complete - no difference - likely because there was contact with the fabric "above" the caps due to the way the legs pushed the fabric into the grass.
I came to the same conclusion as you did. The physical size of the carpet (radius in any direction) is smaller than the effective ground plane of the radials. So at some point the RF will be absorbed into the lossy ground more and more as the frequency decreases and wavelengths get longer and longer.. It seems the ‘magic’ of the carpet is proportional (only to) the radius of carpet relative to the frequency used. If true, then this is good news - because the laws of physics are safe and unaffected by the ‘magical’ powers of the conductive carpet, thank goodness 👍.
Whoops, I meant to say ‘diagonal length of the 4 corners’, not radius - hi hi
It would be pretty cool to hear some WWV comparisons between the ground plane options. Remember folks, SWR is not an indicator of radiation performance (although it helps transfer power of course).
Yes, I may try that, or run some tests and check RBN numbers.
@@w2aew looking forward to it. My hunch though, is that the blanket is simply too small to be as effective as those longer radials. The near field on HF is just enormous and you’re probably getting a lot of loss into the soil. Just a hunch. Antennas are my favorite mystery.
Interesting results, with my vertical I have about 150 radials, mostly made from stripped down network cable. I live in a part of the UK with relatively conductive soil. My limited observations seem to suggest that the lowest ground impedance from the least amount of wire can be achieved with surprisingly short radials. Maybe 0.05 of a wavelength, I suspect your Faraday cloth would work well here.
For such a small area the faraday cloth does seem to be viable...
Nice timely review, as I'm in the market to buy my first antenna!
Excellent Mike! Does that mean you're close to getting your ticket?
Well thank you for that interesting test, gives me some things to think about anyhow. This is something I was going to try sometime but you kind of did if for me, ha. I have a Wolf River coil and 3 longer radials, can't remember how long, maybe 30 ft or so. It works great for me. Hope you are doing well, been a while since I chatted.
Hi Alan,
I bought the 5m long Faraday cloth with the intentions of cutting it into two 2.5m lengths and taping them together. That would give an approximate 8' X 8' ground cloth. Hope it will work better on 40m than the length you used.
Interesting! Some Hams experiment with „chicken wire fence“
Interesting and not surprising that the performance decreased with the decrease in frequency. Looks like for most transient operations like POTA that the radial system works best/easiest. Thanks for sharing Alan! 73 - Dino KLØS
Try doing the same test with out the tri pod sitting on the cloth , but use a jumper to connect to it. Tri pod then the cloth running long ways away from it. should be a lot better.
SWR by itself does not indicate resonance or efficiency. A better analysis would be to determine the frequency of zero (or minimum) reactance that is the resonance frequency. You will then know the resonance frequency. The impedance of a vertical is often near 35 Ohms (sometimes lower) with a good ground. Changing the ground system and keeping the antenna length the same can change the feed point impedance and resonance frequency. Learn about Vertical antennas. Of course any piece of metal that can be tuned will put out some radiation to some where. The question is how much and where.
Thank you for your great comments - all 100% correct of course. In this specific case, I was just investigating the effect of the fabric vs. the radials I typically use and how that would affect the return loss observed by my radio. Not looking for the ultimate in radiation efficiency - for my portable operating purposes - good enough is good enough ;-) and this setup has proven itself good enough.
With the low impeadance 40m and lower, you need a shunt coil or a transmatch. Coil is $5. 7 turns x 3/4 dia. Fun experiment.
Would say the magic carpet would work well in say operating on a building rooftop, like a car park, where it would couple well with the rebar in the concrete. Would suggest putting a metal snap in the middle, and with the other half of the snap a wide copper braid as link, which should reduce some of the inductance there.
Hi Alan, it would be interesting to actually measure the antenna feedpoint complex impedance (R +/- j X) when doing the comparisons as SWR does not tell the complete story (SWR can be very misleading). As an example a full size 1/4 wave vertical will have a radiation resistance of approximately 36 ohms but if you just use a few ground radials it's feedpoint impedance might measure 60 ohms (just a wild guess for this example) which would be an SWR of 1.2 to 1 (36 ohms would have been radiation resistance with an additional 25 ohms of ground loss). As you add more radials the feedpoint impedance will continue to decrease towards 36 ohms as you get closer and closer toward a perfect ground, and when you achieve a perfect ground the feedpoint impedance will be 36 ohms with it being all radiation resistance and no ground losses (ignoring slight copper losses) and the SWR would be 1.4 to 1 which is worse than what we had with just a few ground radials but having the higher SWR is actually a good thing in this example because now we have no ground losses. It even gets more pronounced if you use a vertical that's much less than a 1/4 wavelength long as the radiation resistance of a short vertical gets smaller and smaller as you continue to shorten it. The key is to drive the ground losses toward zero by adding more radials which will at some point start causing your SWR to actually increase, and then if necessary use a simple impedance matching network to match the low antenna feedpoint impedance to the 50 ohm feed line (an L network works great for this). Just FYI, and thanks for the recent POTA QSO. 73, Don wd8dsb
HI Don - I'll have to try some tests with the RBN to see if there is a dramatic difference. I have the saved sweeps, so I can take a look at the complex impedance on the Smith chart for both configurations.
Check out also the comment from WECB640 and reply. Those and yours, Don are all valid. I might point out when considering the practical aspects as Alan is doing (SWR vs efficiency, etc.) that there is the matter of diminishing returns to consider. I won't (too lazy) look up the hard figures that Rudy Severns determined for us but the hams who go overboard putting in radials spend a LOT of time, $$, real estate, copper, maintenance when they go above the 16-32 radial point. See the cover of ON4UN's book. He probably gained no more than 0.25-0.5 db with that radial field vs a 32 radial field. But his goals were completely different than Alan's POTA activity. Fun stuff. 73 to all, Rick K2XT
You can always make a hat from that fabric ; )
To keep the aliens from reading our thoughts!
It seems that the magic carpet is more magical at higher frequencies. How does it perform at 10, 6 and 2m?
Likely much better than 20m and below.
Comparing reception using RBN and some real time AB testing would tell you much more about effectiveness and efficiency. We know using this method that just elevating the radials 3 feet can give you a few extra db
Double the number of radials! And make the extra 4 radials 20ft each. Youll be happy with the OTA results. 😊
I'm sure I would. Since my goal is to make casual POTA contacts, the extra performance I might get with more/longer radials isn't really worth the extra time to setup/teardown as well as the extra space in the go-kit - since I generally make sufficient contacts with what I've been using. Once conditions begin to decline at the end of the solar cycle, then I'll up my game.
It would seem for the bands in question, neither the area of the magic carpet, nor the lengths of the radials would be sufficient. I suspect either double the carpet area or 2x the number of radials (at 1/8 or more desirable 1/4 wave) would yield improvement.
What would also be interesting is a comparison of 'wide strips' of carpet cut to the same lengths as the radials vs regular radials. Additionally, regardless of SWR differences, signal strength comparison at receiving stations.
Fun stuff.
P.S. I probably would take the rubber feet off the tripod.
Hi Chris. Tuning the length of the radials is much more important when they are elevated radials. When laying on the ground, the specific length is much less important. Sure, it has more ground losses, but as long as I make POTA contacts, that's all I care about. I'm not trying to bust pileups or work a bunch of DX, I'm just looking to have some casual operating fun in a park. Certainly, a larger carpet area would help especially on the low bands, but the extra fabric somewhat defeats my purpose of fast and easy deployment. I ran some experiments with the rubber feet removed as well as different (and more direct) attachment of the fabric at the apex of the tripod with little difference noted. I may try to run some comparisons using RBN spots to see signal differences.
@@w2aew Understood. Really just thinking out loud. I've always found my unun end fed has outperformed my verticals on 40m for portable ops, which is why I generally opt for that antenna in the field if there are trees I can fling into. 72!
@@kq2rp Totally agree. When I have the time and location conducive to using the 40m EFHW, that is definitely my antenna of choice. Often times though, I have limited time, or no real good way of getting the wire in the air - that's when I go to my MP1.
@@w2aew golf ball w/eyescrew and spool of fishing line is my weapon of choice. 60' no problem.
@@kq2rp My 8oz throw bag and line are usually sufficient to get the antenna up high enough, but only if I have the time and the trees are available.
Dumb question time, why is there a need for a ground plane, I cant figure out why an antenna would need that to operate. Are there not plenty of antennas that work fine without the ground plane ?
It's not a dumb question. A signal fed to an antenna needs something to "push against". Yes, it's true, there are antennas that don't require a ground plane, and there are those that do. An example of an antenna that doesn't need a ground plane is a center fed doublet or dipole. In this case, the signal can "push" against the other half of the antenna. Picture stretching and relaxing an elastic band between your hands. Each hand works against the other. An example of an antenna that requires a ground plane or counterpoise is the quarterwave vertical. The ground plane becomes the "other half" of the antenna for it to work against. Picture yourself pushing a shopping cart. The only reason you can move it is because you are pushing equally against the ground. If you were suspended in air, you would not be able to move the cart. I hope this helps.
@@w2aew Thanks so much for getting back to me, you explained this perfectly, I finally get it now :) I am currently studying so I can get my ham radio licence, which was largely inspired by watching your videos. Just want to take a second here and let you know that I have been watching your videos for almost 8 years now and your a natural born teacher. Big thanks for taking the time out of your day to make these videos and share your vast knowledge here on the internet. I regularly watch your videos before bed because it just makes me feel good, even though I often have zero idea of what your talking about hah! Anyways, thanks again for the response W2AEW and maybe when I get my licence I can make contact with you over the airwaves. Cheers from Ottawa Canada.
@@UOttawaScotty Very glad to help! Good luck on your studies, and thank you for being a loyal viewer - best regards, Alan
Just as a thought, Have you put the Magic Carpet and the wires out together? My thought is that it will be better than just one of them. Also a larger Magic Carpet should help. Just some thoughts from someone that has not yet tryed this with my Wolf River Coil antenna. Hope to soon. 73 W4DES
Both together would likely work very well. For me though, many parks I go to don't have a nice open area to lay out the carpet (trees, brush, etc.).
Is the primary effect of the radials/magic carpet to couple to the ground or is the most important characteristic to provide a low impedance return path? If it's the second, then wouldn't the current distribution, which shows higher currents nearer the base of the antenna, be helped more by those longer radials as longer wavelengths would have a corresponding longer reduction in current the further away from the base of the antenna? (Sure would be a lot easier to draw that as a picture--grin)
A later edit: this seems to go against the common statement that more shorter radials is better than fewer long radials. Hard to have more radials than a solid chunk of conductive fabric.
Yes, both are important, but some minimum length would typically be needed.
Interesting video. I had not seen this magic carpet before. I suspect, but not at all sure, that a larger magic carpet would perform better at the lower frequencies. Curious if the magic carpet comes in larger sizes
I am sure a larger fabric would work better on lower frequencies.
I think it would be more meaningful to look at the difference in field strength rather than SWR. When you are working with a minimalist ground radial system, a good portion of the base impedance is made up of ground losses. Improving the ground screen might very well reduce the ground losses and put more energy into the field but the resultant SWR would be increased. The classic example is if you had a resonant 90-degree radiator, the base impedance would measure about 50 ohms, 35 ohms into the antenna, and 15 ohms in the ground loss. Improving the ground screen would reduce the ground losses and make the SWR increase, but it would put more energy into the actual radiated field. And of course, require an adjustment to the transmitter matching.
Spot on. A 1:1 SWR just means your transmitter is not seeing any reflected power and says nothing about where the power is going.
Totally agree - far-field field strength measurements would give me a much better indication of radiation efficiency. In my case, I was purely looking at the effect of return loss / VSWR to see the difference that my transmitter would see. I already know that I get sufficient performance with the radials (based on thousands of POTA contacts), so even if the fabric improved it a little, it likely wouldn't be worth the extra effort in setup for me (finding a clear patch of ground is tough in the wood, keeping the wind from blowing it, etc.). My radial system can be easily deployed in about 30 seconds and works well enough for my purposes. I appreciate your good comments.
I am curious if you either take the rubber off your tripod legs or use more jumpers from the cloth to the antenna if that would improve performance.
I ran that experiment after I finished filming. No difference.
Good to know thanks
Would it help to run an additional radial along the perimeter ? My thoughts are that RF flux through a loop would be better than just spokes. All my gear is still in boxes since my move or I'd try now.
I like the idea of the magic carpet when optimizing for deployment speed.
For me, deploying the carpet takes longer than my current 4 radial setup.
@@w2aew Makes sense. The ground where I deploy is extremely dry sand.
really good data. Could you give more details on the size, brand, model etc you used for the magic carpet?
This is the one I used: www.amazon.com/gp/product/B09BDZGXHT/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&th=1
thanks, this whole magic carpet needs a bit of looking into.@@w2aew
I think you need longer faraday cloth for 20 meters and below. 17/15/12/10 you should be good to go. I have ordered 2 x 5 meter lengths (17ft), to form a cross - which I anticipate, will be very good down to 40 or even 75 meters
That’s likely true. I found that the wire radials are faster to deploy and don’t require anything to hold them down in the breeze, so I’ll likely stick with them, even though they’re probably a little less efficient.
Hard to tell which one is better from only SWR. With a pure 1/4 wave element the Radiation resistance could be 35. The ground resistance adds to that and IF the ground Resistance were 15 ohms you might get a perfect match of 1:1 SWR. If you improve on the ground resistance the SWR should increase until with absolutely no ground resistance ( impossible in the real world) your SWR could be 1.4. In that case you made the ground better but the SWR indication got worse! I am sure you know this but so many guys go for low SWR without thinking about the overall picture. However it looks close enough that it probably does not matter which you use!
A more detailed study with RBN reports would likely show that they're pretty equivalent performers. For me, the wires are easier/faster to deploy than the conductive fabric.
@@w2aew Yes, I agree. I use about 3 or 4 short (10 to12 foot) radials and think it gets me good enough. I think any sky wave tests is almost impossible to see less than 3 dB difference with the RBN even due to QSB and other ever changing ionospheric conditions. Even instantaneous switching between my three 10/20 meter dipoles is not always clear. However anytime a signal is off the dead end of one, it always makes a big difference switching to one of the others. 73 de N4DJ
SWR isn't an indicator of well an antenna actually radiates.
4 elevated radials will beat anything coupling to the ground.
Great video. Very interesting. I am not familiar with the faraday cloth.
It is something typically used for RF shielding.
@@w2aew Thanks.
Interesting.....
ty sir for the test video. may i ask what the dimesions are of the Faraday cloth? NS9T
43"x108"
@@w2aew thanx
If another or two more "magic carpets" were added the the ground plane what would be seen? I'm betting the results would be better. Thanks for the video... now you've done it, the wheels are a turning now... kinda like beer, more is better, up to a point...
That would definitely help on the lower bands - but certainly not as convenient for deployment at a POTA or SOTA site as radials would be.
I think it would definitely be better using two or more cloths for the lower bands. And IMHO, I think it would be EASIER for me to stretch out the cloths as opposed to stretching out longer or more radials. Of course, others' mileage may vary.
I've always been a bit skeptical about the magic carpet. Not so much about it efficacy but as to whether they are superior to regular radials in a field deployment. At least with my chelegance MC-750 it takes such a short amount of time to deploy the antenna I don't think laying out the cloth would actually speed anything up.
I totally agree, especially now that I have run the experiment. I can deploy the four 10' radials in about 20 seconds. Easy to do on flat or uneven ground. Wouldn't be so easy with the "carpet". I've been thinking about the MC-750, but not sure how much of an advantage over my MP1. I do like the laser marked whip for tuning. But, wish it use the 3/8" 24 thread to mate up with my various mounting accessories. I guess I could get an adapter... I like the spike for mounting, but so many sites I go to have very rocky soil, it might be difficult.
@@w2aew luckily chelegance sells a tripod for the mc-750. It's an M10 thread so you can always fabricate an adapter. I've designed one that can be 3D printed on printables.
The laser etched band markings make it extremely easy for field deployment and the banana connectors make the radial system convenient too. Takes me about a minute to deploy total
Been using my MC-750 for a few months now, it works fantastic. Better and cheaper the the WRC. Told a friend, he was skeptical, but ended up with one and now wishes he had gotten it sooner.
I too am going to stick with radials. The magic carpet is a fad because of TH-cam, that I think will quickly fade.
Thanks for interesting video.
First of all, I would understand the return loss (S11) better than SWR; however, I can concert SWR to return loss. It is like measuring length in inches vs cm.
Second, one would like to know how the # of radial lines effect the return loss in dB. So 2 vs. 3 .. 10?
3rd, one would be interested to know the directionality of antenna with magic carpet vs. 2 vs. 3 ... 10? To do that one would connect Port one of network analyzer to the antenna and port 2 to a dipole Antenna and walks with dipole on a circle centered at the antenna, and measure magnitude of S21 in dB.
Here we are not interested on absolute magnitude rather relative magnitude at different location.
It would be very difficult to perform that S21 measurement properly for HF (meaning, making the measurement in the far-field).
@@w2aew
Yes you are right.
However we need to measure radiation pattern on the horizontal plane. The normal way of measuring radiation pattern is to put the antenna on rotating platform and then measure the received power in far field.
About the network analyzer you are also right, it is difficult to measure S21 in far field say 10m band; thought, it is not impossible.
Therefore, this gives me an idea to redesign network analyzer with remote probes (ports) that communicate with the main unit using radio wave.
@@aduedc Of course, my interests lie in the 40-30-20m bands, which makes the far field even further ;-). RBN reports are likely going to be the best measure for real-world performance
@@w2aew Yes, and you have to deal with multi-path reflections.
I also recommend simulations using 3D simulator like HFSS or other simulators.
Also one could apply for Darpa grant to make wooden merry go round and put your antenna on top of it. Then one could go to a location say 5 miles away and rotate your merry go round with a stepper motor and remote control.
I wonder what the height of the antenna over the magic carpet for each band would do?
Likely, the closer the better, but I didn't test this.
I tested 20m ham stick on a tripod about 4ft high with 4-8ft radials and my SWR was 1.2.
I also tested 20m ham stick with magic carpet and metal flag stand about 8" from the ground with 4-8ft radials and without and the best SWR was 2.6 in the middle of the band.
I also tried 10m Ham stick the same way with Faraday cloth and I had similar results.
I plan on trying a magnet mount antenna and check results.
Hope this helps. @@w2aew
All the comments do is demonstrate that it is each individual's perception of what works for them. There seems to be no hard and fast proven immutable theory. In my case I gave up on radials for portable ops because they get in the way of the public and I don't want to be on the end of a law suite. Those who swear by radials as some magic solution ignore that most hams just throw them out on the ground so they are not straight but lie in a wiggle and curl everywhere, meaning even if they are cut for resonance well they won't be resonant on the frequency they were intended to be. Quoting AM broadcasters I believe is also fallacious as justification for laying out many radials on HF because they are still using design thoughts of a century ago before there was much if any real understanding and certainly not the measuring equipment we have nowadays. I have used a metal flyscreen and a 5.2m vertical, 9:1 unun and tuner and worked from the outback in VK4 using 100 watts to the USA and Europe on 20m, 15m and 10m SSB in various sites including with extremely dry rocky soil underneath. It works and works well for me. Now I use a similar sized faraday cloth and it works just the same. Radial theory out the window.
I'd stick with the radials. JS6TRQ / WC8J
I'm wondering what would happen if you made kind of a cross of two "magic carpets", with the antenna at the center, of course.
I’m sure it would be better, but I’m not willing to spend another $50 to find out. Best use case for this fabric might be as a tablecloth fir when I use the AX1 on my KX2.
Wondering what the results would be using both at the same time.
Marginally better than either.
Have you tried a test witth both the magic carpet and ground radials together att the same time?
No - I was really only interesting in looking at the cloth as an alternative to, not in addition to, a radial set.
@@w2aew sounds like an experiment I may have to do then.
@@WH6FQE I would imagine that the radiation efficiency will be better than either alone.
@@w2aew That is my theory as well
@@w2aew I ordered 4 of the cloths, along with the tape to seal them together into one large mat. I will do some tests with a single matt with standard ground radials, one with 4 combined mats, and then with the 4 mats and ground radials.
Im not expecting much of a difference between the 4 mats and the 4 mats with radials because of diminishing returns.
Aren't these SWR plots suspiciously flat? This typically indicate very high losses (in the transformer if there is any, in the transmission line, etc).
My success with this antenna system at QRP levels would indicate otherwise.
@@w2aew I also successfully do QSOs with 1W output power and sometimes even 1/4W. It doesn't change that 1W is only 20% of 5W.
@@R2AUK ...which is exactly why I don't worry about it. If my losses are 1dB or 10dB, as long as I am making contacts - it really doesn't matter to me. I am not a contester, so not fighting to get my signal thru - just having fun in the parks.
I don't believe the thin wire would make an RF connection. Maybe DC but not RF. As others said SWR isn't the goal. See if signals are better.
Not ideal, but it works ok. If RF couldn't make it through the thin wires, then ground radials wouldn't work either.
Please measure the DC resistance from point to point on the magic carpet. Hopefully it is a good conductor, but possibly it is not. From a Faraday shield standpoint it might not necessarily be a good conductor. If it is not a good conductor it would not be a great choice for use with an antenna. Although, compared to just 4 radials, even a modest conductor might be OK. SWR and SWR bandwidth are not reliable indicators of a good antenna, i.e. a 50 ohm resistor has good SWR and great bandwidth.
It is very low resistance, just a few ohms end to end.
Excellent! Then it should work well as a ground plane. Don't be discouraged by the SWR and SWR bandwidth. Narrow bandwidth goes along with a low-loss antenna. The radials are likely higher loss, so larger bandwidth. @@w2aew
73s
Cut the magic carpet into strips as radials and redo the test. Shorten the ground lead as well.
Not worth it for me at this point. In the end, it wouldn't be faster/easier to deploy then my simple 4-radial setup.
👍
I get much better with my window screen on 40M than you, typically below 1.4. I wonder if it has to do with your vertical or the ground.
Probably a bit of both
TAKE THE RUBBER NUBBIES OFF THE BOTTOM OF YOUR TRIPOD AND TRY IT AGAIN.. THE ALIGATOR CLIP YOU WERE USING SKEWED THE RESULT. YOU NEED TO HAVE DIRECT CONTACT FROM THE TRIPOD TO THE CARPET..
I ran that experiment after doing the filming and saw no change. This is likely because there actually was contact just above the nubbies due to the way the legs pushed the fabric into the grass and made contact on more of the leg surface.