Re: Availability of Mag Loop and other stuff...

Jack, W8TEE
 

If I were writing a treatise on mag loop antennas, I might worry about simultaneous transmissions and similar exogenous factors, but we're not. Chances are, we will do some simple tests using CW, SSB, and probably FT8 or FT4. We will transmit for a period of time, switch antennas and see what happens. We will be collecting data from WSPR and the beacons, but it is all constrained by the time we have to do such things. Our goal is not to probe the physics of the ML, but rather to provide enough information to those who are interested to decide if it's worth the effort to build a ML. One of our club members is using a dipole on 40M and uses thumb tacks to hold it to the ceiling, bending around 90ยบ corners, yet he's still making contacts. All he wants to know is if he can put one out on his balcony any make contacts with it on 20M.

The good news is that I believe that the construction article we plan should be sufficiently robust that you can build one, too. Then the ball's in your court and you can do the depth of testing you mention. I simply don't have enough grains of sand left in the hourglass to worry about it that much.

Jack, W8TEE

On Saturday, June 1, 2019, 4:45:46 PM EDT, Alan de G1FXB via Groups.Io <g1fxb@...> wrote:


Thanks Jack,

Long answers are good and indicate your willingness for full disclosure.

(Manufactures antenna specifications tend to be BS generators?
Second only to the HiFi industry.??
Remember the kids in the mid 1980's with their "Ghetto Blasters" advertised with 780 Watts of stereo music power, and all from 8X D cell batteries.
In fairness some of the manufactures provided revised figures when used on mains power, nearly a KW.
Man those things must have being efficient, and all through a skinny power cord....)

I couldn't find on the pacciffic66 site what they reference their figures to, on that initial page at least?
hopefully it's something real and not against some theoretical property.
One of which, the proper name escapes me at this time.
(my numbers for instance :-)
6ft of wire whether straight or coiled is a larger percentage nearer a useful wavelength ie: 1/4wave?? at say 28MHz (approx 8ft) than the same 6ft of wire to 14MHz
I interpret this to It's a simple expression of comparison of physical length to wavelength, nothing to do with the antenna efficiency and devoid of losses in the matching networks that are necessary, etc, etc.
Even if it's a real antenna they are referencing it to, it in it's self could be a compromised reference gives great headline numbers.
Check the fine print!

Suggestion:- At least do the theoretical model of what ever you choose to use as the loop reference antenna against a full size centre fed dipole at identical heights, even if not a real world test.
Granted it's monoband & optimally performs mounted half wavelength above the ground but it's a good indicator & reference, and as cheap & simple?? to construct as it gets.
if you don't like what you see in the comparison it's between you and your conscience.
You can cripple it's performance and justifiably conclude an XYZ antenna, is greatly more efficient than?? a halfwave dipole when mounted at 15ft agl for example.... :-)

Saw the reports of doing A/B comparisons, however quick the changeover there is always the element of doubt as to propagation.
the ideal is simultaneous TX to both antennas in the same lot but far enough not to interact is the goal.
In the real world two antennas one each in the same town is good enough. What's a mile over a propagation distance of say 6,000??
everyone has their preferred mode, be it CW, WSPR the latest digimode.???? Reality it doesn't matter?
The requirement is for as many & widespread coverage of receiving stations as possible??
That said, QRP-Labs kits are cheap enough to utilise two, and compare like for like WSPR time slots to each of your and AL's callsigns allocated to each different antenna?


regards Alan

On 01/06/2019 17:27, Jack Purdum via Groups.Io wrote:
Alan:

The results right now are modeled using the usual Pacific66 app. However, we do plan "real" tests in an attempt to get some useful data. Our reference antenna will likely be an 80-10M EFHW which we both use. Al also has a vertical that we might test against. However, the EFHW is always available; not so with the vertical.

We read in a paper that someone added a ground plane and said it "made a difference", whatever the hell that means. Anyway, because of that, we want to try it and see if it does have an impact. We have already noticed that the shape of the feed loop makes a difference, as does its position in the vertical plane. The effect is small, but real.

Al and I have talked about this a lot, and our feeling is to publish the results of the "Double-Double" as a construction article. (I want to call it the "Luggable Double-Double" but Al's not happy with that.) There are controllers out there (Loftur Jonasson) so my feeling is that will be kept for the book only. Also, it will be somewhat unique in that we hope to add a TFT display that shows the SWR in realtime as a plot. We have arranged to have all of the projects' PCB's available at a reasonable price.

Al and I are writing the book in a strange way. We are going to finish it before signing with a publisher. The reason is because I know the time pressures that editors put on authors with respect to deadlines and we want to get this right rather than to market fast. Our TOC has 18 chapters, of which the first 4 are really setting up the software for the Arduino, Teensy, STM32, and ESP32 ??C's and giving the beginning reader enough C instruction to read our code (and shoot themselves in the foot a few times?) We see 12 projects in the book, some of which (e.g., the ML) are two chapters--construction and software. Some are "end products" (e.g., the ML, a different antenna tuner, CW messenger, CW decoder, CW Tutor) while others are test equipment (e.g., programmable power supply, AC voltmeter, signal generator). The last chapter is on using what you've built to troubleshoot a receiver. We think it will be a very unusual, but useful, book. Our goal is to have it done by the fall. We currently have 9 chapters done.

Long answer to a short question...


Jack, W8TEE


On Saturday, June 1, 2019, 12:01:46 PM EDT, Alan de G1FXB via Groups.Io <g1fxb@...> wrote:


Hi Jack,

Sounds like you are on to something special with 90% and even the 40% are impressive figures.
(Noted that they are modelled?? efficiencies at this point in time, here's hoping with can you can achieve something approaching in practical tests.)
To what reference antenna (also at the same modelled height to compare like for like) ?

Interested in your comment the trials of a counterpoise,
Previous papers indicate loop type antennas were considered a free space antenna requiring no ground plane / radials
I guess it's the feed / matching & counterpoise is where the magic happens?

As it's using an auto tuner is the write-up destined for your new book is there an ETA, or another perhaps magazine article release?

(One gotcha about some of the previous, (not your) small "miracle" antenna's.
Check it's actual the antenna doing the radiating and not the feed line, or counterpoise even the mounting pole has being known to be "accidentality" hot with RF.
(However disguised, generally any antenna employing a braid breaker / balun in the coax away from what they make you believe is the feed point or suggested feeder or support lengths perhaps warrants a second look.))


regards Alan

On 31/05/2019 18:45, Jack Purdum via Groups.Io wrote:
We are also trying to assess other factors, too, such as a counterpoise and its affect on performance. We may find that these "other factors" play no significant role in the antenna's performance. Still, learning that something doesn't matter is as helpful as learning what does matter.

Jack, W8TEE

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