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

Ad-hoc day-to-day VHF SSB activations

Words of nuance, words of skill
And words of romance are a thrill
Words are stupid, words are fun
Words can put you on the run

1 Like

Oi, he was speaking to me! Mind you, I wouldn’t dream of it either. I did try to get the idea of horizontal FM across, but it was firmly rejected. Their loss, not mine. I’d had a ball anyway working plenty from the summit… the end of a long day and I went home well chuffed.

Nothing.

My logbook only exists when I am on a summit. I haven’t had a home shack QRV for a few years.

So I only assess general activity ffom the ease with which I qualify SOTA activations with a handheld.

Without doubt, it’s on the up.

Believe me, I really hope you are right. Its been too good a party for it to just fizzle out!

WARNING - ON TOPIC ALERT !!

Gerald (G4OIG/G8CXK) and myself (G4MD/G6GGP) are hoping to go on an ad-hoc trip round the “Shropshire 5” on Monday 20th Jan using 2m and 70cm ssb, horizontal and vertical polarisation as required. Hopefully will stir up a bit of activity! Still in the early stages so watch out for further details and approx. alerts to follow but note first summit will be around 0800 so attendance by the “breakfast club” would be appreciated!

Hope to see a bunch of you on Monday :slight_smile:

73 de Paul G4MD

1 Like

We had that in this thread:

I havn’t fixed my tcxo until now :anguished: … it’s still at the shelf - but the time will come.

I think, that the transverters for the other bands might have the same problems…nevertheless is an interesting possibility for everyone who has a qrp device for 10m. The transverter is cheap and light.

73 Armin

I look forward to having a go at chasing you both. Under normal circumstances I would probably have gone up a hill for an attempt on at least one s2s - however, I shall have to be home based as the boiler is being replaced and I will have to be around all day.
The contest equipment (UKAC) should do the job OK - horizontal beam 2m & 70cm plus dual band collinear. The QTH is on the South slope of a low hill so no actual los Northward (never any IO83 or 84 contacts) but probably near enough for SOTA. Power will be off from time to time but I have already done the necessary beam rotation and have quite a good supply of batteries for the radio.
Hope you have a good day - it was lovely in the Forest of Dean today.
73,
Rod

Many thanks Rod sorry to hear about the boiler… Sounds like you’re well prepared anyway! Will be looking for you :slight_smile:

73 de Paul G4MD (or G6GGP for this expedition!)

My alerts finally up! (Only a day behind Gerald…) We’ll try to keep as closely as we can to the times but it’s a pretty hectic day to fit the five summits in… We’ve allowed 30 mins operating time per summit, hopefully this will give a reasonable balance between experimentation and getting round them all. Hoping we’ll get to WB-004 just in time to set up in the light…

Hope to catch some of you tomorrow,

73 de Paul G6GGP

I hope to work you, but 2m and 70cm were unuseable today due to a powerful pulsing noise. I have found which house it is coming from and will approach them tomorrow - wish me luck!

There’s an unmentioned issue also to be mindful of, and that is polarisation twisting. Every reflection causes some distortion of the wavefront. I hypothesise that there is greater twisting of vertically polarised signals than of horizontally polarised signals. I suggest this may be why horizontal polarisation works better for marginal horizon-skimming contacts. So in fact the station with “only” a vertical antenna should not give up on signals known to be horizontally polarised such as big gun tropo dxers out at 300-500 km. The vertically polarised signal from the portable half wave or multiple half wave vertical will not end up being purely vertically polarised after a few close encounters with hilltops, trees, buildings, radio masts etc. Similarly the horizontally polarised signal from the bay of 4 x 12 el yagis that the dxer proudly uses does not remain horizontally polarised. Some of the QSB on long paths is due to polarisation twists. We know this because experiments with circular polarisation reveal much reduced fading on incoming signals. Circularly polarised antennas receive equally well any polarisation from zero to 180 degrees offset from nominal. (Some may say, equally poorly, but then, why would commercial fm broadcasters use circular polarisation? The 3db nominal loss is far outweighed by the reduction in polarisation twist fading. )

What this means, in summary, is that the hypothetically pure conditions between two antennas on a testing range, line of sight, with lab equipment connected to measure every molecule movement, are not the same we use in the field, where we learn to ride the waves of QSB, waiting for the signal that went down to come back up again. The VHF dxer knows this phenomenon well.
Even in towns, signals that are regarded as vertically polarised do not stay that way. In the 80s and 90s I used to enter local DF competitions (“fox hunts”) on 2m, which used fm signals, transmitted using nominally vertical polarisation, but I was always using a horizontally polarised beam. I almost always was first or second on the site of the “fox”. I never observed the theoretical 40 db of polarisation loss. It’s just not there in practice.

I read a nice analogy by someone comparing polarisation loss and the precision required to achieve it, with the precision required in a balance modulator. With only a few things not perfectly balanced, the carrier suppression was degraded to 20 db or less. If you’ve built a tube based balanced modulator you know this to be true. (Same applies to “balanced” feed lines).

How likely is it that an antenna with a semi horizontal and imperfectly isolated feedline, not perfectly vertical or stable due to wind gusts and surrounded by reflective and refractive trees and buildings and towers would be able to maintain perfectly vertical polarisation? Not very… so there is really no such thing as “vertical” polarisation from an amateur portable antenna, ie. the ones we use on summits.

Phew, apologies for the long post. This thread is too tempting to ignore…

73 Andrew VK1DA/VK2UH

2 Likes

Good luck with sorting your interference Brian you have my heartfelt sympathy! Hope to work you. Several times :slight_smile:

This is not to say that circular polarisation is without its own problems. The theoretical loss between left hand and right hand circular polarisation is similar to that between vertical and horizontal polarisation, so transmitter and receiver must agree, and an oblique reflection can reverse circular polarisation. Rotation of linear polarization is dependent on reflections and exactly what happens is dependent on the geometry of the reflections as well as their strength.

One of the advantages of horizontal polarisation is that it can follow non-line of sight paths through diffraction. One of the disadvantages of vertical polarisation is that on passing through trees it is more strongly attenuated than horizontal…dependent on the type of tree, of course!

It is all in all a very complex subject, and Andrew is right to advocate caution in applying theory to the real world. As hams our policy has always been to “suck it and see”!

2 Likes

My J-pole pole is normally propped up against some rocks or other handy object at the summit. So this means, on hearing a weak 2m-SSB signal, I should try leaning the pole over a bit in different directions to see if the signal strength improves.

This effect in well demonstrated by this YouTube video microwave polarization demo (which I used to do as a A-level Physics teacher). Skip forward to the 6-mins mark …


[Sorry about the big image - normally there’s an option to reduce its size or show just the link]
I guess you would need a neat line of evenly-spaced wet pine trees to be anywhere as bad as the metal polarizer used in the demo.

The main problem with trees I’ve encountered at SOTA summits (e.g. Grange Fell GM/SS-249, Claife Heights G/LD-053, Wendover Woods G/CE-005 [the clue is in the name]), is being surrounded by densely-packed wet trees where you get big attenuation regardless of polarization, especially on the microwave bands.

1 Like

Brilliant job done today Paul & Gerald on the Favourite Five (No idea about how Gerald went on with 70cms no gear or aerial above 2m).

However Paul - you did a fantastic job and obviously finished Titterstone Clee Hill in the dark. 100% success for me - worked you on all five summits, furthest distance between us 239 Km to Titterstone, nearest distance summit Brown Clee Hill 231 km. Heard G0RQL at R5 on all 5 summits, distance 503 Km.

At this end 100 watts from IC-7400 to Wimo 7 element cross yagi, fixed to pole on house, horiontal polarisation.

73 Phil

2 Likes

Worked Gerald on Long Mynd from Titterstone Clee Hill today around 13:00 UTC, I was using a 70cms Moxon horizontally polarised, no dip in signal if he was using a vertical… Not worked out the distance as the drive back home has worn me out.

If it works it works!

2 Likes

Yes, I do this with my J Pole and it makes a difference, espacially with AE contacts.
Compton

Many thanks for the 70cm SSB S2S yesterday Dom. I was afraid that I had missed you when I didn’t hear you when I was on Stiperstones, but we made it when I was on The Long Mynd on account of you being delayed. I was running the 817 barefoot to the 6 element DL6WU yagi at 2m on the Mynd to keep as low a profile as possible. Thankfully there were no wardens in evidence.

Having the 6 element slant polarised was interesting. It didn’t seem to affect the results with those horizontally polarised using yagis and worked well with those with vertical colinears. One unusual effect was that I was found to be stronger on vertical polarisation when beaming away from a station. Obviously the side lobes are somewhat strange with the antenna at 45 degrees. However, when beaming directly there was a good correlation between the horizontal and vertical elements. I was most impressed by the fact that Don G0RQL worked me on all 5 summits and for expediency I only ran the 817 barefoot on two of the summits. The downside to all this was that my design orientated mind was severely affected by the ugliness of the appearance of the antenna at 45 degrees! :laughing:

I will prepare a write up of the day in more detail, but would like to thank all that came on to work both Paul and myself. Indeed Don G0RQL and Adrian G4AZS worked me on all 5 summits… and Rod M0JLA would have done, but for some reason we didn’t make contact when I was on Corndon Hill. More accolades to follow in the write up.

73, Gerald G8CXK / G4OIG

An update: the offending unit turned out to be a Samsung branded fast charger. When powered up but not doing any work it generated a wide band chuffing noise that could be picked up on a quarter wave whip on 2 metres and 70cm at a distance of a hundred metres! In future it will only be turned on when needed. I would offer to replace it out of my own pocket but I suspect that as a branded item any replacement would be just as bad!

Pleased to hear that you got this sorted Brian… or maybe not. It would have been good to have been able to work you on 70cm yesterday. I assume that you have shown them where the off switch is for the charger. All you need now is for their brains to be engaged. :grinning:

If anyone is wondering is how I mounted the 6 element at 45 degrees, well here is the mount taken from the PIR part of a defunct security light. It was one of those “what are you keeping that for?” items scorned by the XYL. The diameter just happened to be such that with a bit of filing it fitted directly into the top of my pole when reduced to 4 sections. Simplicity indeed.

2 Likes