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Lightweight Vertical Antennas


#63

Thanks for the information Heinz.

Bravo Emil - an admirable operation - SOTA extreme at its best! I note on two summits DL8JJ was QRV at 0015z and 0330z…

As I need to sleep and do other things I only captured 3 summits - the ones I was present in the shack for when Emil was on the air. What appears to be a loaded vertical on 40m CW at Emil’s end did the business. I imagine if I had been listening to all 7 activations I would have worked Emil on them all.

One point to correct - Emil only completed 6 first time activations Heinz. Lutz DJ3AX beat him to it on DM/TH-853 Halskappe. I missed chasing him but got Emil later in the day!

73 Phil


#64

FYI Phil, Emil could not be heard here from summits #1 and 2 …

You’re right Phil, this has been written because Emil published his plan for the 7 first activations at an early stage at SOTAwatch and Funkamateur.de

To be 100.00 % correct :wink:, the antenna Emil used on summit #1 was an OCF Dipole 404-UL from spiderbeam.

BTW Phil: Points, rankings and records are for me with 70 no longer of great significance. To be QRV on the mountains gives me a lot of fun, hi.


#65

:+1:


#66

I have used an MFJ1979 for a 1/4 wave 20m SSB vertical


The radials do take time to lay down…


#67

How many radials were you using? They appear to be well elevated.

Andrew VK1DA/VK2UH


#68

I used between 4 and 16. 8 seemed to be a good compromise between radiative resistance and time to lay out. The radial length were adjusted for lowest SWR depending on ground conditions. Snow is better than rock! The feed-point for both radials and vertical is typically 2m above ground. Three separate guys were used. I operated 20m SSB, the low take off angle gave me typical QSO around 3000km
Walker VA6MCB


#69

Did you try it with just 3 radials?

This is one of the perennial subjects, how many radials, how long, how high…


#70

I tried 2 radials on one particular peak that was more of a knife blade shape. The SWR was high and needed my ATU. The local geography was probably equally responsible for the poor ground (1000m + drop offs on 2 sides)


#71

3 1/4wave radials at 45deg gives an excellent match to 50ohm. For your antenna that means the feed point would be at 3.5m AGL.


#72

Keep in mind that the feedpoint impedance is not the radiation resistance and minimal SWR doesn’t have to happen at resonance.

An elevated L/4 vertical should present ~50ohm impedance with 2-4 radials sloping at 45 degrees depending on wire thickness and enviroment. Do the tips of the radials sit in snow ? Because they might be detuned this way and that’s why you needed so many of them. Second theory would be that the antenna is resonant outside the band, the number of radials lower the resonance impedance so SWR at resonance is bad and the length of transmission line transforms the in-band impedance to a value close to 50ohm.

Razvan


#73

Summary of my understanding of this issue.

Elevated radials - ground losses are minimized but they should each be full quarter wavelength with end effect adjustments for resonance. And ends should be insulated.

Radials on the ground. 32 recommended but length not critical as they get detuned by proximity to ground. 120 used by BC band broadcasters. Aim is to overcome ground losses which are bad enough in good agricultural land but are huge on a rocky mountain.

I prefer elevated radials as you need fewer of them, so much quicker to set up. Modeling predicts only small loss (<1db) in efficiency between 3 and 16 if elevated and resonant. I use 3 on 20m.

Modeling also predicts heavy losses from a system using short stray bits of wire strewn around the base of a Ground mounted vertical. Even if they are given a mysterious name. Good on CB verticals but not for real antennas.

This is mostly well covered by the standard handbooks from RSGB and ARRL

VK1DA/VK2UH


#74

Totally agree !


#75

I went along to the G-QRP Convention on Saturday, one of the lecture sessions was a Q&A with Roy Lewallen, W7EL; the author of EZNEC software and all round antenna knowledge source.

I asked Roy about using vertical antennas vs and inverted vee for SOTA. Roy gave a very comprehensive answer, in which he concluded that in almost every case, the inverted vee would outperform a vertical on a summit. Roy stated that ‘take off angle’ is not a good measure of a DX antenna, rather it is the field strength in the wanted direction that matters.

After all the ridiculing I had about stating my beliefs and findings that the inverted vee antenna is effective for SOTA DX, I was pleased that a leading expert also aligned with my views.

Roy’s session was very informative and a lot of ‘pennies got dropped’!

73, Colin


#76

Hi Colin

That is most interesting; thanks for asking. Was the session recorded so that we can hear Roy’s views?


#77

I’d like to hear that too. As I am a bear of little brain can someone explain what the real difference is between take off angle and radiating field strength in the wanted direction. My level of ignorance is you pick the antenna that radiates mainly to where your target is and you know where the antenna radiates by looking at the plots for its take off angle etc.

His own software suggests there are heights AGL when an inverted V is a damn fine antenna for DXing and heights were it isn’t. So it would interesting to see if the software designer’s talk matches the software designer’s own software predictions!


#78

I still believe in my vertical.
DG7ACF/p complete SOTA log Inverted-V @ 6m agl (20m - 10m):

DG7ACF/p complete SOTA log vertical @ 3m agl (20m - 10m):

Ahoi
Pom


#79

It would be nice to understand how to ensure that condition is met…

Adrian
G4AZS


#80

Hi Pom,

That looks pretty conclusive, but is your selection of antennas truly random, and have you spent the same amount of time using each? Spread across the same group of summits? Lots of desirable background info springs to mind…

I haven’t tried to test alternatives, and have no strong views, so it is all interesting to me.

Adrian

G4AZS


#81

Hej Adrian,

this is my complete SOTA log, regardless of which summit I was on. I just filtered all QSOs with my vert on 20m through 10m and did the same for the linked inv-v. My selection of antenna is obvously not random ;). You can tell from the number of pictured QSOs that I’m a dedicated vertical user and the inv-v is more like an alternative or spare antenna. Anyway, it’s some W1 and EA8 (not even a real DX) vs. the whole world… :wink:

Ahoi
Pom

PS: Most of the DM summits have woods on them. Nevertheless I mostly use the vertical. :sunglasses:


#82

Add to the fact you need to know which direction to set the inverted V up in to get that lobe to the DX, if you set it up “wrongly” that lobe will send your signal in the wrong direction.

You haven’t always got the luxury to set up an inverted V in whatever direction you choose. With a vertical you just need a small amount of space in comparison.

So whilst theoretically I agree, practically I don’t. The proof is in actually using them in anger on a cold wintry morning, most of the more “successful” SOTA DXers are using verticals. myself included.

I do use my inverted V on 20m, with good results also. I do generally find its better on receive sensitivity.

YMMV

Jonathan