Suggestions for a practical small area 80m antenna for SOTA portable use

Ed,

Consider the following, which is an all-wire, resonant, and lightweight antenna:
A U–shaped, all horizontal antenna as follows: Imagine a dipole for the 15-meter band, (about 7 meters long), center fed with a 1:1 choke balun, say 2 meters off the ground, and say running East-West. Now, connect wires at each end of the dipole, both of these wires running say to the North (or both running South). These wires will be about 17 meters long, and will run parallel to each other, both also 2 meters off the ground. The length of these wires are trimmed to be resonant at the frequency of interest. They load the dipole, and they cancel each other in the far field. Because the dipole part is (roughly) about 1/10 wavelength, this is a “magnetic” antenna, and so will be somewhat quieter than a full-size horizontal antenna. The resulting antenna is 17 meters long, 7 meters wide, and is fed at one end; that it requires 4 support points is an inconvenience; however, its other attributes make it very attractive. I’ve used this antenna with excellent results in various forms, but not yet as a SOTA field antenna. By the way, if the loading wires are connected with links, just the dipole section can be used for 15 meters during the same activation.
Best,
Ken, K6HPX

I believe this one is available again from midnight tonight, but only for a limited time.
Compact and does DC to light.
80m should be no problem, I think you can leave it in your backpack if space is at a premium.

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Thanks Ken but for that reason, your antenna doesn’t meet one of the major requrements, that of fitting a small space on a summit.

Ed.

Only works for 24 hours - correct?

To be honest, the requirement you made looks to me more and more as a
theoretical desk exercise.

Why: Among the many hundred SOTA summits there are several dozens that are excellent locations to set up a non-compromise antenna for 80 or 160m.
Therefore, why not turn the question posed and ask for appropriate 80/160m summits?

… and if you really think of things like the Matterhorn then simply pack a MP1DXTR80 SuperWhip Antenna :wink:

73 gl +

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SmallIsh space requirement is not just because of physical space restrictions on a summit but also to avoid impacting access for other visitors to the summit.

I do not want to have to drive 3 hours to a summit with enough space to put out an 80m antenna, just so that I can operate on 80m!

My thoughts are that as the higher frequency bands become unusable through worsening propagation and the migration of amateurs from those bands to 40 metres fill it up even more, 80m could make a good alternative for SOTA activations as long as we can solve the antenna size issue, which can be an issue on some summits.

Please feeel free to start a new thread to look for 80/160m compatible summits if you wish to.

73 Ed.

It’s those damn laws of Physics Ed. Either it’s
A) big physically and works well
B) big electrically and works not-so-well. (for various definitions of not-so-well)

The choice is A or B.

You can improve the odds by choosing activation times to avoid the worse time for D-layer absorption and increasing your signal to noise ratio by using modes with more Watts/Hz i.e. not AM, SSB or FM.

… as the upper bands …

Thanks Ed, no need in this matter.

Or you could use a German cuting edge antenna Ham Radio Site - [CUTTING EDGE ANT]

73 de Pedro, CT1DBS

Yes, I thought I was going to hit those damn Physics laws again. I just need to find a workable compromise - I still have some good ideas from the thread - so thanks to all who have contributed.

Ed.

Got that one direct from Rick this morning, thanks Pedro,

Thanks Heinz - text corrected.

The responses so far have been great, food for thought as the cycle goes down. Now to just find some antenna wire that’s strong enough to support a long antenna wire (I currently use 13x0.12mm).

It might also be the only 160m activity I do as my backyard isn’t really big enough for a 40m dipole.

Silly question and the answer is probably “sometimes”, but is 80m likely to be useful at all in the sunny part between grey-lines?

check on the SOTA news for Sept 2015 An Antenna Story by PA7ZEE.

The article is actually in Oct 2015, not Sept

73, Barry N1EU

More likely in winter than in summer. During the summer daytime D layer absorption can leave 80 dead, sometimes 60 and even 40 can drop out.

Brian

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Hi Ed,

Many use the G5RV or ZS6BKW on 80m quite successfully. No coils to wind or adjust. Plain straight wire. Twin line feeder. Usable impedance on 80m, with ATU. Not as short as 40m dipole but shorter than standard half wave dipole.

Query on your loaded dipole. Is the coil made as a closely spaced coil on a former, as per the article, or is it scramble-wound. Photo appears to show it as uneven, but maybe that’s ice? What wire did you use? I’m just surprised that it is not performing well.

I learned some time ago that loading coils need to be high quality and wound with low loss wire, as heavy as possible and ideally silver plated. Like in a rotary inductor.

73 Andrew VK1DA/VK2UH

Perhaps the answer is to go vertical.
A kite or helium balloon sky hook (or hybrid) is all you need.

Helium has the advantage that you can inflate the balloon at the trail head and then use the balloon as a pack goat,to take the weight of your pack!

I’m planning on playing with some kites during the summer months.

Pete

Careful Pete, didn’t you loose a bothy bag sometime ago :slight_smile:

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Hi Ed,

Yes, you are hoping for a bit much as others have pointed out. I have used half a dozen different antenna systems for SOTA over the last few years and IMO the gold standard for local contacts is a resonant dipole for contacts out to about 700 km and a vertical for longer distances. The vertical however requires more real estate as 3 minimum quarter wave radials above ground are needed for best performance.

The 44 foot doublet is as long as you can use for 14 MHz and above if you don’t want too many nulls. It’s OK on 30 m and usable on 40 m but is certainly shaded by the full size dipole. That’s where the 88 ft doublet picks up the pace and it is usable on 80 m but with some nulls on the high end of the HF spectrum.

If the 44 ft doublet is small enough you could make it work better on 80 m by having clip on coils with wire tails of say 6 ft each. That still makes it a bit shorter than a 40 m dipole. Or you could insert the coils 6 ft in from the ends of the 44 ft doublet. Requires some time experimenting but a coil with self resonance on 14.3 MHz would be my starting point.

Good Luck

73
Ron
VK3AFW

Re 80 m in daylight.

The answer is “Yes, but…”

As Brian said, the D layer soaks up the signal and this absorption increases as the sun rises. 80 m typically loses its effectiveness a couple of hours after sunrise and does not recover until after sunset. It is latitude dependent.

VK3CAT and VK3BYD have used 80 m CW to get into the 40 m skip zone in mid morning and up to UTC rollover but it’s a desperate measure that doesn’t always work.

73
Ron
VK3AFW

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