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

Does height matter?

In reply to M0MYA:

http://www.flickr.com/photos/53695273@N00/361631454/

=)

Ah, but you don’t say how successful it was Dave. :wink:

Recently I’ve been thinking about a simple horizontally polarised antenna with gain. I seem to recall seeing a design for a horizontal collinear dipole (that’s probably a contradiction in terms) some years ago made out of coaxial cable, but I’ve not been able to find it on the internet. I use coaxial collinears at home for 70cms and 23cms FM - http://www.rason.org/Projects/collant/collant.htm I suppose therefore I should get off my backside and waste a bit of RG-58 or RG-174 trying out what I think I saw.

73, Gerald G4OIG

In reply to G7CNM:

Hi Dave, I was on Leith Hill G/SE-002 today and
heard you on 145.575 MHz at around 13:55z. What
power and antenna were you using? I did attempt
to return your call, but just had 5W and a Slim
Jim so might not have reached Lincolnshire…

73, John M0VCM (aka 2E0VCO)

Ever thought about a collapsible HB9CV? There is at least one available consisting of pieces not longer than 38cm. It is a gain antenna and you can use it for horizontal and vertical polarization depending how you fix it at the pole. They are so nice I once even built a portable stack of three of them (the work at the site is better worth some hours of contest operation not only a 4-qso-activation).

In reply to G7LAS:
Hi Rob,
Thanks for the QSO after which I listened to you calling cq shame you couldnt get any more contacts unfortunately I didnt have any means of spotting you with me.
Dave G7CNM

In reply to M0VCM:
Hi John,
Very interested to know you could hear me, at one point I heard a very weak cq sota but just couldnt pull it in may have been you.I was located on a back road between Claxby and Nettleton 150m asl 60w 3ele beam.
Dave G7CNM.

In reply to G4OIG:

In reply to M0MYA:

Ah, but you don’t say how successful it was Dave. :wink:

It was OK - not fantastic. I think 5 or 6 contacts perhaps, using the old FT-290 MK1 barefoot. I was very wet behind the ears in those days so I might not have been operating all that keenly - I’d like to give it another go these days.

Recently I’ve been thinking about a simple horizontally polarised
antenna with gain. I seem to recall seeing a design for a horizontal
collinear dipole (that’s probably a contradiction in terms) some years
ago made out of coaxial cable, but I’ve not been able to find it on
the internet.

http://www.sm0vpo.com:800/antennas/7db-colinear.htm

Is that something like what you are thinking about? I stumbled across it the other day while considering phasing arrangements.

73,
Dave M0MYA.

In reply to DL8MBS:

Ever thought about a collapsible HB9CV?

Hi Chris,

The answer to this question is yes, many times - along with other designs such as the Moxon. The matching section can be an issue on the HB9CV so a kit-built model would most likely be easier to set up than a homemade one. However, I am not convinced that an HB9CV offers much advantage over a standard yagi for SOTA activating.

One aspect of my type of SOTA operating is the ability to get the station set up as quickly as possible in order to maximise the time available for making contacts. It certainly helps to have a quick set up when the WX is bad. With this in mind, I have been experimenting with simple wire antennas for 2m. Yesterday I tried out an extended oblong to the design by Martin DK7ZB, but could not get it to match properly - no wonder he suggests an ATU for the HF version! :slight_smile: It is not easy getting gain without complexity, So far the simple delta loop with 2.4dBd gain seems to be the best option. It is also quite small, so hopefully can be raised to a higher level than a small yagi. Whether this gives the antenna an advantage remains to be seen.

73, Gerald G4OIG

In reply to M0MYA:

Hi Dave,

Thanks for the comment on the slim jim. It looks like it might be worthwhile trying one out sometime. Thanks also for the SM0VPO design information - that’s really interesting.

The design that I was thinking about something was similar, but using coax for the elements as this shortens the required length - even so it doesn’t take many elements to make it quite a size. Thinking back, I seem to recall that the original reference to the antenna was in Technical Topics in RadCom, maybe in the 1970’s (LOL) and it may have been for a high gain fixed VHF antenna for military use where the required direction of fire was known. It would have to be supported by two poles - hardly SOTA friendly. :slight_smile:

73, Gerald G4OIG

In reply to DL8MBS:

Long before SOTA I used to go /P with an FT290R1 and an HB9CV. I had trouble at first with the antenna going out of tune until I worked out that I had the matching section on the top of the boom and in damp conditions water puddled on the top of the square sectioned boom and changed the tuning: it was somewhat more stable after I started setting it up with the matching section on the underside of the boom but was still prone to detuning. I now use one for the home station on 6 metres and it is still prone to showing a high SWR on wet days. I like the high F/B ratio but will eventually replace it for something more stable - I like the idea of the Moxon!

73

Brian G8ADD

Ok Gerald,
I had a commercial one consisting of a H-frame of less than backpack-size and 4 extensions for the 4 half-elements in the H-frame, so it was easier and quicker to unpack on the site than a completely collapsible one. It worked through one contest- and portabel season including one night with heavy rain (maybe luck).
Just for the fun of it the HB9CV-3-stack a bit lower on this site http://www.dl8mbs.de/40993/home.html
:wink:

In reply to many:

Perhaps the question is wrong. It’s not “does height matter?” but “at what height does increasing the height stop mattering?”

When in doubt look at what the commercial boys do. If height AGL didn’t matter much then commercial VHF users wouldn’t pay through the nose to build 50-100m towers, mount their antennas up near the top and run damn expensive feeder back to the equipement rooms. Hell, the towers are on well sited high ground to start with, so it obviously matters enormously that some will pay to mount the antenna nearer the top rather than bottom of the tower.

The evidence exists to show that the antenna height AGL does matter for SOTA activations and that mounting 2m VHF omnis at 2 and bit wavelengths AGL is still not high enough to counter terrain effects. You can see it from the maps of chaser locations I’ve produced.

Andy
MM0FMF

In reply to MM0FMF:

True, Andy, and much as I suggested yesterday: the commercial guys have the money to build a permanent structure to chase diminishing returns much further than we can with a portable structure set up in minutes. Height matters but so does weight and speed, we have to balance the effort we can put into a portable installation against the expected returns, and a ten metre roach pole is a much less convenient portable structure than a 5 metre roach pole!

73

Brian G8ADD

In reply to G8ADD:

If they were “diminishing returns” then the commercial guys would not be interested. They wouldn’t build higher they’d build more lower towers.

Here’s one. Why a cell phone towers the height they are? Especially in urban areas. It’s not to effect greater coverage. A 900MHz cell phone antenna held at typical ear height is 6 wavelengths AGL. If you work out the horizon distance for 1.6m you’ll get 4.5km which is massive for a cell. Why are the base antennas so high to cover a small area? Could it be because ground reflections are such an issue?

The question is “does height matter” and the answer is yes, most definitely.

Andy
MM0FMF

In reply to MM0FMF:

Of course it matters, Andy, but my argument is that to us other things matter, too. On top of a hill you already have a substantial amount of height, a few metres of extra height will only make a substantial difference if the other summits that constitute your horizon are only a few metres higher than you are.

It is worth putting cell towers higher not because of ground effects in the way that I believe you mean, but because the ground is rarely flat: in a depression if you can’t see the tower then you get little or no signal, they are avoiding (or in a hilly place like Birmingham, minimising) holes in the coverage.

I continue to maintain that for practical purposes we balance the advantages of extra height against the disadvantages of extra weight carried and extra time putting up and bracing a higher mast, and of course extra loss from longer coax - which at some point will overwhelm the advantage of extra height!

As for diminishing returns, do you accept that past a certain point the advantage gained from extra height becomes smaller, or do you think that you can continue pushing the antenna up higher and higher until at an infinite height you get an infinitely strong signal! :slight_smile:

73

Brian G8ADD

In reply to G8ADD:

On the occasions I have used VHF on activations I have always tried to mount the antenna as high as practical. On very “Pointy” rocky summits increasing the height would not bring much improvement at all, however, on those with large flat areas at the top (most of the summits I have activated) increasing the height does make a difference.

A good example would be G/SP-001 Kinder Scout, which despite its height can be a challenge to qualify on 2m FM using a handheld if you operate from the true summit. You may well find that more distant chasers give you better reports than those only a few miles away, but shielded by the summit plateau itself.

For HF or MF I try to mount my linked dipole as high as possible to avoid ground losses, but at 160m even at 9m AGL I have a feeling these would still be quite significant.

It’s always good to experiment though :slight_smile:

Best 73 & happy Easter to all.

Mark G0VOF

In reply to G0VOF:

A good example would be G/SP-001 Kinder Scout

Ding, ding, ding, ding, ding… we have a winner! :slight_smile:

Absolutely spot on Mark. On two activations I have been quite disappointed by performance from my simple J-pole. They were on Kinder Scout and Long Mynd. Myself and Brian G4ZRP had walked well over a km up up the river bed from Kinder Downfall to get some altitude. We operated from a big flat wet peat plateau. Whilst we worked 70cms and 23cms OK the 2m performance was not good. Antenna was the 300Ohm ribbon J-pole with the base about 3m AGL. I was expecting to need a big stick to beat back the chasers. As it was it was hard going. Likewise on Long Mynd where performance to the North was poor. Elsewhere it does what I expect. It’s not brilliant but it is so simple, light and easy to setup. Perfect for SOTA in the right part of the world.

Look at the OS map… Kinder is a big flat plateau, Long Mynd has a ground very gently lowering to the NE. Now maybe, just maybe, a few cm more height would have made an improvement. But it’s hard to know how many. In absolute terms doubling the height would make an improvement. Although in my case, the J-pole feeder wouldn’t reach the ground :slight_smile:

http://www.moosedata.com/sotamaps/chaser_locations/ShiningTor-2m-no-yyy.html
http://www.moosedata.com/sotamaps/chaser_locations/KinderScout-2m-no-yyy.html

Looking at the difference between the two summits. The steep drop off the SSW round to the N of Shining Tor makes a wonderful location to work from as it looks over a massively dense area of people. Note these results have been De-Delilah’d! Mike has done so many more activations of Shining Tor compared to Kinder Scout that he skews the results. Also he’s operated from Shining Tor during some fine tropo openings which also skew the results further. The results will include a range of antennas and heights AGL and powers. Red for 2m-FM, blue for 2m-SSB.

It would be enlightening to play with the same antenna at differing heights from Kinder and map the changes. Sadly for me, it’s a long way to come just to prove what can be seen every time you drive past a commercial antenna site. :slight_smile:

Andy
MM0FMF

In reply to MM0FMF:

“In absolute terms doubling the height would make an improvement.”

Indeed, but besides increasing your feeder length you would have to carry a 10 metre pole, and in my case a 14 metre pole now I’ve stopped using the 10 metre pole, otherwise a 20 metre pole - obtainable but too heavy and cumbersome.

“It would be enlightening to play with the same antenna at differing heights from Kinder and map the changes. Sadly for me, it’s a long way to come just to prove what can be seen every time you drive past a commercial antenna site.”

And of course, there is a good reason why the commercial antennas are not twice as high - the equation between cost and benefit!

73

Brian G8ADD

PS The lower summit of the Long Mynd is northeast of the Pole Bank summit and several metres lower, there is an excellent view of the north horizon from the trig point with the ground falling steeply away to the north. A favourite haunt of mine for over 50 years!

In reply to G8ADD:

This is going nowhere fast.

73

Richard
G3CWI

In reply to G3CWI:

You are right, Richard, a fun argument but going nowhere. I shall desist from further rejoiners!

73

Brian G8ADD

In reply to G8ADD:

rejoinders I think!