Antenna mounting question(s)

[Captain Fantastic]

Thanks for confirming it should 'work'! Mine's a silver rod type, so that is good regards whipping around with the kids on there.

Novice question: the trampoline verticals have a plastic sheath over them (see photo - they are green). When mounting the antenna does it need to be electrically connected to the pole, or can I just bolt it over the plastic and forget it (preferred)?

[InTheClouds]

That is a good question. The first answer would be it needs to make electrical contact so the antenna has a counterpoise.
However there is a school of thought that antennas can be isolated from their mount which is typically a pole of some kind.

However this is when an antenna is designed with ground plane radials. A 1/2 wave end fed is not one of these antennas although
there is an argument that any opposing current of which the laws of physics dictate there must be, must flow somewhere and that somewhere
could be the outer braid of your coaxial cable which is to be avoided as it can cause RFI and or other problems in your radios operation.

In short it should make electrical contact for a 1/2 wave end fed vertical.

Firstly you must ensure that the antenna bracket is mounted at the highest point on any upright parts of the trampoline.. i.e. the radiating element should not have other metallic objects parallel to it otherwise you will have SWR issues.

There is also the issue of grounding to consider in a permanent install with regards safety in an electrical storm but I am unable to advise on that.

[The Collector]

At least if you're hoping to do a bit of dx'ing, mounting the aerial on a trampoline will help your signal bounce around the world (had to get that one in, sorry)

[Captain Fantastic]

@ The Collector - very clever.

Well the PO says delivery on Monday, so if I am quick I might be able to mount it up straight away. Otherwise it won't be til Thursday, but then in time for the next local SSB round which will be a good test.

[The Collector]

Cool, keep us updated on your progress

[Captain Fantastic]

OK it arrived!!!

I didn't mount it on the trampoline yet, but instead put it on the upper terrace temporarily attached to a concrete base umbrella stand
Have not even SWR'd it, but it comes in at 1.2:1 already, so not going to touch it just yet.
Put a CQ out and got a guy 11km away who reported a 5 7 and I gave him 5 7 back. He was using a balcony antenna. Could clearly hear a guy 18km away, but didn't try to speak to him.

I'm still on the old RG58, but have put the connectors on the new RG213.

Cannot do much playing around tonight, but will be back on it Thursday, and probably put it on the trampoline then.

Um. It is TALL ! ! ! 5m lying down seems much shorter than when it's poking in the air!

[The Collector]

The more that clears the surrounding buildings, the better. I fully understand you not wanting it too high though as I've gone through that myself with housing covenants and planning laws being ...ermmm.. mis-interpreted

[andrew013]

Also the T2LT on a 10m-12m fibre glass rod the ideal static mobile antenna.

your ideal and my ideal static mobile antenna differ somewhat as mine are a 9ft whip as back up and use a 4 ele yagi and an imax2000

[Captain Fantastic]

I managed to get around to working on it yesterday. First I just put it back up where it was on the terrace but with the new coax to check it was working OK. While doing that I managed to talk to Ernie outside Birmingham who seems to pop up on DX all the time. It was a 5 x 9 call both ways! Very happy with that - 965km.

Then I tuned in later for a local SSB round but reception was terrible. So not being sure what was going on, I decided to move the antenna to the trampoline. It comes in about as tall as I drew above, so that's OK. SWR is a little higher 1.5:1 at one end of 40 so I will adjust that today. I did run a wire from the antenna mount to the pole, as the pole is protected by a plastic sheath and there is no connection.

So I went back on air and still could not get the SSB'ers. However, I joined an FM round a few cantons west of me between 30 - 65km away. One guy was 5 x 9, another 4 x 7 so I was happy with that. The guys in the valleys I could not hear well, if at all. We have some 'small hills' in the way which don't help!

So today's tasks are going to be to find a good route for the coax, and also to get the SWR down a few ticks.

[InTheClouds]

Also the T2LT on a 10m-12m fibre glass rod the ideal static mobile antenna.

your ideal and my ideal static mobile antenna differ somewhat as mine are a 9ft whip as back up and use a 4 ele yagi and an imax2000

I did not say it was my ideal static mobile antenna, but in context of this topic as a T2LT was mentioned (always a good idea to make your reply relevant to what has been asked, maybe take note ) for the majority doing static mobile who want a 1/2 wave antenna it has a lot going for it. Light and easy for portable set up and vastly outperforming a 1/4 wave tank whip.

[andrew013]

[quote=and vastly outperforming a 1/4 wave tank whip.

vastly outperform you say ya certainly in the clouds allright

[InTheClouds]

Given the T2LT antenna tip height would be 6 to 7 meters above that of the tank whip, and possibly have lost a capacitive coupling (which is fairly inefficient) from a mag mount, reduced the ground losses, plus increase in the height of the antenna current centre, that is vast. I would expect to see anywhere between 2 - 4 S points, difference.

Being heard or not being heard is a vast difference by anyone standards, but don't let that get in your way of what is clearly your main focus.

[Captain Fantastic]

OK, so I've had it up for about a week now, and played around. Here are some findings and I'm looking for any advice (apart from "mount it higher")...

Photo 1 is the situation as mounted.

1. situation.jpg

Photo 2 is a closer view of the way it attaches to the upright. You can see there is a sheath it is mounted over, thus preventing any direct electrical connection between the antenna and pole.

2. mounting A.jpg

So far I have tried with no electrical connection, with a 2.5m wire vertically hanging down from the antenna bracket (connected and not connected to the pole at B - blue line), or the same wire at approx. 45deg (also connected and not connected at C - red line)

Photo 3 shows the above wire configurations.

3. radial options A B C.jpg

Therefore I have 5 combinations, reduced to 3 since there seems to be no difference if the wire is connected to the trampoline frame or not.

The resulting SWR on EU channels 2, 20 and 39 are:
1. no wire: SWR = 1.5, 1.6, 1.6
2. vertical wire: SWR = 1.3, 1.4, 1.5
3. 45deg wire: SWR = 1.0, 1.1, 1.25

I have also adjusted the antenna length 5cm either way from the start (and current) length, but shortening (-5cm) had no impact, however lengthening (+5cm) made SWR go up +0.1 across the board. The antenna length from bottom bracket to tip is 5.70m

So what do you think...
- should I have the wire on at all?
- is it worth to connect it or not to the frame?
- why is 45deg wire 'better' SWR than vertical?
- should I leave the wire at 45deg?
- what is the likely impact to my Tx of either of these setups?

Yesterday the weather was good, and it was quite busy on FM. I talked to a guy 60km away who was 5 7 and he gave me 4 4. Another guy 9km away was 5 9 and gave me 4 7, and a guy closer but behind a big hill was 3 6 and he gave me the same 3 6.

I am thinking that I won't get much more than 7 out with it so close to the ground, and 'behind' the house per the picture I posted before.

Anyway, thanks for any input!
Ian

[The Collector]

For the sake of a few minutes, try it touching the metal on the trampoline. Get a report from the same person before/after and also note your own meter readings too.

As it's a that height, you may find it a bit directional, due to the trampoline's metalwork pulling the signal towards it slightly. Turning the trampoline round may make a very slight difference so you could turn that (pardon the deliberate pun) to you advantage, getting optimum signal direction towards where you talk to most..or where you want to reach slightly better.

If you can mount the aerial on a 3m alloy pole (and get away with it) it'll make the signal more uniform (circular, rather than slightly oval) because it won't be drawn towards the trampoline's metalwork quite as much, as well as perhaps clearing more obstacles and possibly therefore getting out a couple of miles further. Only you can decide on that though

As for why the swr is better at 45 degrees etc, perhaps its further away from the framework most of the time??? Aerials and swr can be funnily things. The lower the better though, especially if you ever want to use an amplifier. Under 1.3 would be nice though.

[Captain Fantastic]

Well yesterday afternoon I managed to do some testing with the help of a guy about 14km away.
The result was that 45 degrees and not connected to the trampoline frame was the best. He noticed a big drop off in signal when the wire was hanging down, and also if connected at 45 degs. So now it's left at 45 with no connection!

Interestingly, we had very good radio and signal, and we tested across FM, AM, USB and LSB. That was in the afternoon around 2pm. Then there was a SSB round at 7pm and rapidly the background noise levels increased to the point that after 30 mins I had to drop out as I couldn't hear anyone any more.

I also figured out he has a web SDR so I played around with the vertical silver rod and the horizontal wire dipole to check out the differences. I'll put those up later, but basically the dipole was terrible on FM to the SDR QTH while being OK on AM and SSB.

Then I tested my very old Cobra UK 25 using the vertical and found that the radio & signal was as good as the Jackson II... Both radios gave even better results on UK FM. So maybe I need to shorten the vertical a little more?

I found another SDR in the opposite direction, did some testing from the vertical, and today will test the dipole to that location.