For an HF antenna I am using a mesh dipole (10sq meters) with surprising good results on 7MHz how does it work?

Question

I try to use attic antennas I experimented an antenna made of 10sqM of chicken grid with excellent results how to calculate the aperture of such an antenna the first resonance is 3.6 MHz and the use of twin lead allows for a resonance on 7MHz the ratio of power output to rf measured by the rf meter before the antenna is close to 0.9.

I tried many configurations different areas of grid and length of cable. I was using a Rig Expert antenna analyser, the results seem better than my usual dipole and many ssb qsos were made, barefoot, up to the other side pf the ocean. However as says N6BT when the conditions are good you can make a dxcc with a light bulb, which is why I try to understand a bit more. I could not model this antenna with the usual antenna softwares and I suspect something about antenna aperture and capacitive antenna.

Answer 1

As you say many things can be used as an antenna, but this one actually looks pretty good. You have two electrically large objects (meaning at least one quarter wave long) and they're separated and connected in the middle to a feedpoint. This is the definition of a dipole antenna, yours is just a bit lobsided. It should work pretty well for transmitting and receiving, for the frequencies where the VSWR is low enough.

By cutting it and adjusting the two-wire line you have managed to make it resonate where you need it, so I would say you are done, enjoy it! You could experiment making the loose wire more vertical or more horizontal, to see which works better for your band.

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If you want to compare the performance of two antennas I recommend the digital mode WSPR. You can be up and running in 10 minutes:

• install the software from here, start it up and put in your callsign and grid locator. Set it to transmit every period, as you're doing a short experiment, not a long term project.
• tune your rig to XX.110 MHz, SSB, set for the lowest power you can
• hold the microphone close to the computer speaker, with an elastic band around the PTT
• start the program transmitting, let it transmit one or two complete cycles.

Open up https://www.wsprnet.org/drupal/wsprnet/map and search for your callsign, you'll see all the places you were received, and the strength.

Then change antennas to the other one you want to compare, and repeat.

The difference between antennas may be visible immediately in the number of places that can hear you, or you may have to look through the list of spots and check the received SNR of a few nearby stations.

This is what a strong station looks like today in 10 minutes:

And this is the top of the list of spots, the SNR number is the one you want for antenna comparisons.

Timestamp           Call        MHz         SNR     Drift   Grid    Pwr     Reporter    RGrid   km  az  Mode
2022-07-29 22:44     KB0VYG      18.106148   -18     0   EN11vi      0.2     EA8BFK      IL38bo      7356    72      2 
2022-07-29 22:44     KB0VYG      18.106249   -20     0   EN11vi      0.2     EA8/DF4UE   IL38bp      7354    72      2 
2022-07-29 22:44     KB0VYG      18.106157   -22     0   EN11vi      0.2     WA2TP   FN30lu      1936    84      2 
2022-07-29 22:44     KB0VYG      18.106169   -24     0   EN11vi      0.2     KL3RR   BP51ad      4175    320     2 

Answer 2

When you say surprisingly good results, I take it you've tried other antennas and/or have surprisingly good measurements and in that case maybe you just got lucky. Any metal near the antenna, such as wiring of your house will be coupled to some degree and thus become part of the antenna. If I were you I would experiment with this but make notes of exactly how you have it now so you can get back to that state. Who knows, maybe you can be the inventor of a new antenna, people do it all the time. If you think you've got it figured out try it on a different house, if it works well there too you might have something and if not maybe you just got lucky with what you have.