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Author Topic: VERY small 80m antenna  (Read 1678 times)
VA2DV
Member

Posts: 168




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« on: January 28, 2019, 05:54:49 PM »

I would like your inputs about what would be the smallest, usable 75/80m antenna.
That can be installed on a balcony.

I dont expect great perfomance, just something to have a presence there.

Some ideas :

- A Chameleon loop with the extra 80m turn
- A dipole made of 2 mobile antennas back to back
- A single 80m mobile antenna with some counterpoise

I have already a broadband Diamond vertical but it’s a no go on 80m.

Let me know your thoughts and suggestions.

Thanks in advance.
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WY7CHY
Member

Posts: 921




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« Reply #1 on: January 28, 2019, 08:05:18 PM »

Get a tarheel or similar screwdriver antenna. Then, instead of a large groundplane, use hamsticks as the ground plane. I've attached 2 80m hamsticks temporarily to the base mount of a screwdriver antenna and made quite a few contacts on 80m. And with it being a screwdriver, it can be adjusted for other frequencies.

A friend had a screwdriver mounted on his vehicle, and when he sold the vehicle he didn't want to keep the screwdriver for his new car. I didn't want the screwdriver for a vehicle, but he sold me the entire thing cheap. So I mounted on my house chimney and wound up adding 2 long wires for 80m; 2 medium for 40m, and 2 smaller for 20m. Works great.

You mention a balcony, so I can only assume you mean an apartment type environment. If you don't have enough room for a screwdriver, you can try a taktenna. I have tried a homemade version of this. It actually works. Not the best, but definitely makes contacts. They make an 80m version. go here: https://www.tak-tenna.com/
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
KR4BD
Member

Posts: 303




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« Reply #2 on: January 29, 2019, 07:22:37 AM »

About 20 years ago, I was temporarily working in Rochester, NY.  I stayed in a house with a second floor bedroom with an adjacent balcony.  I bought the 80 and 40 meter Isotron antennas which “everyone” said were “junk” and would not work...but I had worked several people who used them when I was operating from my home station in KY.  I mounted them on a 5 foot mast and strapped it all to the wooden railing on the balcony.  I ran a ground wire from the mast to a water pipe at ground level directly below.  Well, with these antennas I was able to maintain a weekly Sked with friends in Ohio and Indiana on 75 meters.  I also worked a DX station in Germany on 3795 and have the QSL card to prove it.  Many other “surprising” contacts were also made.  My setup included an ICOM IC-706 Mk2g (100 watts) with an AT-250 auto tuner, using RG58 coax.  The Isotron antennas DO HAVE A very narrow bandwidth, but you can easily adjust them (on the antenna itself) to what part of the band you want to use.  The antenna tuner will give you a little more operating “elbow” room without having to go outside for adjustments. 

These antennas are a obviously a “compromise situation”.  I am sure many will have negative comments about the Isotron, but I can tell you that if you follow the instructions and watch your SWR, these antennas WILL work in a tight spot.

Tom, KR4BD
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WY7CHY
Member

Posts: 921




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« Reply #3 on: January 29, 2019, 08:43:42 AM »

Another option if you want to go REAL BASIC. (But it does work, I have tried it). Is a hamstick octopus.

Check this out.
https://www.gigaparts.com/mfj-2104-hf-600w-quad-band-octopus-antenna-w-75-40-20-15m.html?gclid=EAIaIQobChMIsMv_3LST4AIVy4x-Ch3kYACwEAEYASABEgKPsvD_BwE

It's designed to run 4 bands; e.g. 80/40/20/15m. 20m and 15m actually work quite well. Basically it's a dipole using Hamsticks.

I have tried it put ALL 8 hamsticks as 80m. (I have access to a lot of hamsticks; mine and ham friends). Basically, using ALL 80m hamsticks, I got a decent omnidirectional antenna. Worked fine for IN-State NVIS nets. I also experimented using 4 hamsticks at 80m and 4 hamsticks at 40m and using a tuner, I was able to also tune in 20m and 15m. Lot of options.

Of course, $470 for this is a bit expensive. If you just want a plain hamstic dipole with just 2 elements; you can get an mfj-347 for about $20. Put 2 hamsticks on it and have a mini dipole. You can swap out different bands. 80m, or 40m, or 20m. Just have to manually change out the hamsticks.
https://www.gigaparts.com/mfj-347.html?gclid=EAIaIQobChMI2u2wxbaT4AIV9R6tBh2wQgq1EAQYASABEgIB7_D_BwE

Again; FWIW: Hamsticks on 20/17/15/12 meter actually work pretty good. 40m and 80m aren't that great. BUT, they do work. Especially if you just want In-State net control NVIS use.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
N8AUC
Member

Posts: 493




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« Reply #4 on: January 29, 2019, 09:45:33 AM »

For 80 meters, don't waste your money on two hamsticks in a dipole configuration.
I tried that once. Darned thing was deaf as a post. Even when tuned to resonance, it couldn't hear anything.
And when it was tuned to resonance, the usable bandwidth was miniscule. Maybe 20KHz at best.

Now the "hamstick dipole" probably works fine at 14MHz and up. But for 80 meters, you're better off looking at almost anything else.

73 de N8AUC
Eric
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KB2WIG
Member

Posts: 612




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« Reply #5 on: January 29, 2019, 01:11:09 PM »



If you hung some wire on your railing, and let it reach the ground, how long would the wire be?

KLC
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EXTRALight  1/3 less WPM than a Real EXTRA
LA9XNA
Member

Posts: 257




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« Reply #6 on: February 11, 2019, 01:59:02 PM »

Use a online shortened dipole calculator.
https://m0ukd.com/calculators/loaded-quarter-wave-antenna-inductance-calculator/
You will need a antenna analyzer or low power (QRP) and a swr meter to tune the antenna.
Just remember that the coil is also dependent on the material in the coil of the core.
PVC gives high loss so use some other plastic material on the core.
PVC insulation on the conductor in the coil will also alter the impedanze of the coil so it is smart to add a few extra turns while winding and then remove some when measuring.

To check the inductance of the coil connect a 50 ohm resistor, low tolerance capacitor and the inductor in series. The simplest way is to use a lenght of coax 5-10m and someterminal blocks.
Keep the inductor, resistor capacitor assambly away from any objects by suspending it by a thin tread from above. Connect the antenna analyzer or transmitter (low power 1W) and SWR meter.
Find the lowest SWR.
By making a series resonanze the SWR will be close to 1:1 when in resonance.
Use the resonanze equation to calculate the value of L.
Remove one turn on the coil and redo the measurement and calculation. Then you will know the number of uH pr turn and it is simpel to get the correct number.

A tip if you dont have low tolerance capacitors.
The tolerance will be halfed when dubeling the number of capacitors.
if you have 10% capacitors put 5 in paralell and you will be accurate enough.
10%/2 =5%
10%/4 = 2,5%
10%/5 =2%

A few words about the resistor.
Use non inductives and when using a transmitter remember that the rating of the resistor must fit the transmitter.

Links
http://www.i1wqrlinkradio.com/antype/ch13/chiave1648.htm
https://www.nonstopsystems.com/radio/frank_radio_antenna_80m-dipole.htm
https://www.hamradiosecrets.com/short-dipole.html
https://www.eham.net/ehamforum/smf/index.php?topic=38790.0
http://www.bvarc.org/pdf/Antenna_Loading_Presentation_Sept_2015.pdf
https://www.nonstopsystems.com/radio/pdf-ant/antenna-shrt-dipole-bvarc.pdf
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