Other SOTA sites: SOTAwatch | SOTA Home | Database | Video | Photos | Shop | Mapping | FAQs | Facebook | Contact SOTA

Advising needed for 14 mhz gp antenna


#1

Hi!
I’m planning to build a vertical GP antenna for 14 mhz and after some google search I have already some question without a clear answer, so I would appreciate very much some assessment from aerials experts!

  • Would be 3 radials enough or, would it be much better with 4?. You know how the things can complicate when wind and wires are together on the summits, but being so low over the ground, could be the difference (isolating the radials and the ground antenna system from the soil) significant?

  • I would set it up on a 6 m glass fiber mast. I’ve read f.i. at http://www.qsl.net/df3lp/projects/vertical/ that 0.25 lambda would be ok. (the antenna would be only 0.6-0.7m over the ground). High enough?

  • Would I have to put a 1:1 balun or RF choke? I’ve read that YES/ NO / IT DEPENDS is the right answer :frowning:

Thank you,
Mikel (waiting for the rain to stop to have some carrots)


#2

My 12m 1/4wave GP had 3 radials sloping down at 45degs, the bottom of the radials was just above ground and the feed point was about 1.5m above ground. I didn’t use a balun. I worked VK, W6/W7, Z21, VU etc. with ease on 5w CW/SSB.

With radials, unless you have perfect symmetry and installation, one radial will “work” harder than the others, so 3 work as well as 4 when they are elevated.

If I remember the maths for the geometry, I don’t think a 20m antenna will fit a 6m pole, a 7m pole is needed.


#3

I would go for the largest pole within reason Mikel to give you flexibility to try different configurations. I have been playing a lot recently with GP verticals and they are certainly impressive and interesting.

You can build a 5/8L and use 1/4L radials (see below), this will lower your feed impedance and you get lower angle radiation.

Here is what I am doing next for a 5/8L I can give you the formula if you want. Using stub matching

But this would require a 12.5m pole unless you load it :wink: , on higher bands it becomes more practical.

As the page suggests the GP height is a factor in radiation patterns, and not necessarily the number . But its also a question of efficiency with QRP.

Jonathan.


#4

Hi Mikel,

I’m using a 1/4L vertical on a 7m fishpole. I’ve made some MMANA-GAL simulations and 3 elevated radials are enough, but 0.6-0.7 off the ground it is a bit low. My radials start from about 1.5m and sloped to something like 0.4-0.5m
Maybe you can add some stiff wire or something at top of antenna (as part of the radiator) so you can feed the antenna at about 1.5 - 2m from groud.
I don’t use any balun or choke for my vertical.

73,
Petronel


#5

Hi Mikel

From experience not hearsay;

  • 3 radials are plenty, the more radials you have the more tangles you can get.

  • My main 40m vertical and my 20/17m “holiday” antenna have the radials on the ground.

  • Direct feed, no choke or balun.

Very simple antenna to build and it will work.

Carolyn


#6

Hi Jonathan

The co-axial stub is how I get my 40m vertical to load on 17m, the only difference is I leave the “40m” radials in place.

Carolyn


#7

Yes you gave me the idea :slight_smile:

So roughly its ~10m of wire on the radiator and on the GP (x 3). You load it as a 1/4L on 40m and a 5/8L on 17m ?

hence you bypass the stub with a switch or similar.

Jonathan.


#8

As W. Edwards Demming said “A man without data is a man with just an opinion” .

Just about anything will work Jonathon, some designs are less lossy or more efficient or more tolerant of setup variations

For a 1/4wave, sloping radials from the feed to ground at 45degs results in an almost 50 match. So elevated radials make the match simpler.For 5/8wave, the impedance is of the order of (typically) 180-j300, i.e. capacitive so you need j300 or inductance to get the reactance to zero. Then you need to transform 180 to 50 so you can use 50ohm coax. There are lots f ways of doing this. For QRP you need to ensure you minimise loss here.

Are ground radials bad? No but there is lots of evidence showing they are more lossy. Is this loss bad? Maybe. Or Maybe not!

One of the most important factors for antennas for SOTA is how quick can you set it up when it’s cold and windy and does it stay setup or do you need to faff about to get a good match. A quick to setup antenna that is not bothered by ground changes may well be worth the lower efficiency. So you need to iterate around the design, build, measure and refine loop until you get performance you are happy with.

Software like MMANA-GAL which is free lets you experiment without cutting wire. I think 4nec2 does better ground modelling. Both are free. You can play with wire thickness, radial position and size and design for gain or pattern. An expression involing “free lunches” springs to mind as well.

This is one bit of amateur radio that anyone can play with. Copy designs from the net, see if they work, play with the software and try new ideas to see if they work.


#9

Absolutely well said, Andy.

My own contribution here:
Sometimes I use a 1/4 wave antenna with a single elevated radial on 20m.
Due to the velocity factor of the wire (PVC isolation effect), the length of the radiator is about 4 meter (!), so that I put it in a 5m pole with feed point at abt 1 meter over ground. I play with the radial length to tune for best SWR, that I always achieve with ease.

My antenna includes a simple UNUN at the feed point, design as described here:

For QRP power leves I use another toroid; a T50-2 with 15 turns both primary and secondary. I guess without this UNUN it would work all right as well…

Probably the antenna would work better with 3 elevated radials instead of 1 but I want a fast setup and so far I feel fine with the performance obtained.

Good luck and experiment to get your best solution.
VY 73


#10

Yes but unfortunately most of this “data” is opinion. "I worked XYZ countries on Ant “A” doesn’t appeal to me which is the problem analysing antennas. But then again its impractical to build an antenna test chamber at these frequencies at home…

You can judge on only two things - experience and simulation. The first most people class as opinion.

I know you can impedance transform practically anything and make it radiate. No problem. To make it radiate at QRP on a 10m pole optimally is where design and optimization come in as you state.

You haven’t got a lot of choice with a 10m pole in my example you can not change the angle. The loss seems tolerable from others peoples “data”. Design trade offs are always going to bite.

The design above that I suggested seems to be a good compromise. I am solely sticking to verticals now as dipoles are becoming a PITA to setup on some summits, and are putting an unnecessary strain on poles in high winds.

This is a good text. It inspires me anyway.

http://www.eagle3.net/n4ywn/docs/PracticalAntennaHandbook-vol4.pdf

Engineering - you can always do better and you can always learn !


#11

Hi Mikel,
I think the posts here will give an idea on what you are looking for.
My 2 cents,

  • I use GP at ground level with radials laying on ground most of the times with pretty good results. No balun. RG58 directly connected.
  • In the beginning I had 8 radials about 5m long each, but some time ago I reduced to just 4 and roughly speaking, I find no differences, so I’m now thinking on possibly reducing to 3 or even 2. I’m sure there won’t be any difference from 4 to 3 and probably very little and almost unnoticeable with 2.
    Do activators worry about directivity when using an inverted V dipole? It will be about the same if you use a GP with 2 radials 180 degrees spaced.
  • It’s true that a ground mounted GP has bigger losses than an elevated one with the radials sloping down at about 45 degrees, but even though I keep doing the ground mounting because it allows me for an easier and quicker set up. Given the amount of QSOs and even great DX I work during my activations, I don’t really care about the higher losses of the ground mounted GP compared to the elevated one. But it’s up to you, of course, and you’d better set up your GP elevated with radials sloping down and keeping their ends above the ground by about half meter minimum if you want to maximize your GP performance.
    I have got my ECO mobile antennas this week and once I had adjusted them for good SWR while mounted on the roof of my car, I’m planning to try them on a mast or fiberglass pole with one or two wire radials sloping down at about 45 degrees for use on SOTA activations. I hope to try them this weekend, weather and family duties permitting…
    Best 73, Guru

#12

Hi Jonathan

This is how its done, no switches.

The section between the blue connectors (at the bottom of the picture) and the base of the “antenna”/ red radials is removed for 40m.

Next thing you are going to ask is how I get it to work on 20m :smile:

I like this by Andy;

One of the most important factors for antennas for SOTA is how quick can you set it up when it’s cold and windy and does it stay setup or do you need to faff about to get a good match. A quick to setup antenna that is not bothered by ground changes may well be worth the lower efficiency. So you need to iterate around the design, build, measure and refine loop until you get performance you are happy with.

All I can add is that once you realise that portable antennas are going to be compromised in some way getting something that is simple and gives reliable contacts while you are cold and wet in the middle of nowhere always beats the multi-band bit of wire that needs a tuner.

Carolyn


#13

Totally agree after this last WB ! Just trying to work out the maths as its slightly different to the articles example, but prob not far off.

Think I might cheat and jump on the VNA.

Thanks for the detail Carolyn.


#14

I think your antenna is more tolerant than mine is Carolyn… I do have to faff about now and then. Sometimes it’s simply deploy and use and other time it can need adjustment. However, it fits on a 5m pole so I suffer the faffing about for that fact alone.


#15

Hi Mikel
I use
6m pole (easier to carry) or 7m
With 4 radials - slightly of the ground .5m with 6m pole or on the ground
(Plannig to reduce to 3 radials to get less tangled wires)
No balun
T1 (optional)
73 Angel
Built in Tenerife at the Parador in 1hr!
Ps. I will be building a 10m version soon


#16

Just found and article about elevated radials. 2 per band seems to be enough if elevated

73
Petronel


#17

Thank you, Petronel, and all the others who have given their valuable opinions and references.

I have read all the given material and some other which I think could help us to understand how verticals GP aerials perform and which can be the best way to built and adjust them later while being on the field (on the summits in our case)
I think some aspects could be pointed as of interest, specially these two:

  • Radiation angle as a factor of elevation over ground
  • SWR, antenna efficiency and ground losses.

I’ve also found some papers on the net which deserve to be read as well:
http://www.astrosurf.com/luxorion/qsl-radials.htm
http://www.qsl.net/df3lp/projects/vertical/ (give special attention to radiation patterns)
https://rsars.files.wordpress.com/2013/01/study-of-20m-quarterwave-vertical-elevated-ground-plane-antenna-1-31.pdf

Finally, I’ll try to make some tests (the materials are ready), working with 3 (slightly) elevated radials, first on a 9m rod with the feeding point at 4 m AGL, and 2nd, the same antenna but on a 6m pole with the feed at, say 0.5/0.6 m AGL.
I’ll try to give you my results later.


#18

Hi Mikel,

I won’t pretend that my antenna is perfect or “the best” but it works, is relatively quick to set up and I have had reasonable success working EU LP from VK using either 5w or 10w cw and ssb.

I use 3 radials. I try to keep them above ground as much as possible so the return current flows in wire instead of lossy ground. The feedpoint is around 1.6 to 1.7m above ground and the vertical radiator goes almost to the top of my 7m pole. I don’t use any transformers, baluns, ununs or resonant lengths of feedline.

A photo of the feed termination is included in my field day photos just posted. https://flic.kr/s/aHsk9we7Zs

73
Andrew
vk1da


#19

One problem that I’ve noticed with my vertical is: Because of low radiation angle and the null at vertical angle, there is hard to make QSO with someone under 1000km. But this is normal, and not so many SOTA chasers so close. Sometime, if I have time I’m trying to use linked dipole for 40m and give some chance to YO/HA/LZ chasers.

73,
Petronel


#20

That is one advantage of the 40/17m design is that you can switch between two different bands with different characteristics easily without having to reach up to the antenna or use a tuner etc.It is possible to load it onto 20m as well as Carolyn has said.

I use a separate vertical at the moment which is 1/4L on 15m with an extended linked top to make it resonant on 20m. The 4 wire CP stays the same length though, to be truthful my noise floor isn’t as good as it could be on 20m, but its a good compromise and works well enough.

There are many solutions to the squid/SOTA pole antenna mounting arrangement. My observation of most activators setups air on the side of simplicity which is understandable and keep to simple designs that work. But now the summer months have arrived hopefully the weather will be better and thus allow more delicate structures to stay up.

Wire is cheap after all.

I was speaking to a guy on 40m that designed this before the chasers arrived on GW/NW-020. When I looked him up I found that he had done something interesting with a slot antenna. Which allows for switched phasing on a single pole, a clever design I thought.

http://www.g3vcg.talktalk.net/

Jonathan.