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High static level - which HF-Antenna?


#1

Last Saturday I had to give up the attempt to operate from OE/ST-033 “Grimming” due to thunderstorms around and static discharges. A low profile 25m wire started arcing to ground. Even a center loaded mobile whip for 7MHz (about 2m high) got “hot”. It was a challange to get the lw and mobile whip packed for the way down. This is not the first time I had some electrifying experience. Is there anyone who knows a proven portable antenna design which allows to operate at such increasing static levels common to summits?


#2

In reply to OE1HFC:

Hi

I would question whether you should actually be there in such conditions? The chances of getting injured or worse are surely too high.

73

Richard
G3CWI


#3

In reply to G3CWI:
Richard, we are well aware of assessing the risk and how to move or shelter in case the conditions get worse. But simple wire antennas even short mobile whips are obviously inadequate for increasing static as you hear nothing but crackling noise. I’m looking for some experince how to cancel or at least reduce the noise to allow to operate. I guess loops or grounded antennas (half bazooka dipole?) could do better in such case but I have not tried yet.


#4

In reply to OE1HFC:

operate. I guess loops or grounded antennas (half bazooka dipole?)
could do better in such case but I have not tried yet.

I used to ground my loop antenna, but recently have not bothered to do it any more. In my case the bottom part of the loop is on the ground anyway. I thought that the 2.5 W QRP would not really be dangerous into relatively large antenna. But I can not compare to other antennas since I have done all my activations with the same antenna, power, tuner and radio always on 30 or 40 m.

73, Jaakko OH7BF/F5VGL


#5

In reply to F5VGL:
Jaakko,
Thank you for the interesting report on using loops. Based on your experience I will experiment with a wire loop with total length of appr. 30m with the KX1. That worked with the internal ATU on 20,30 and 40m but with the wires up in the air. Did you ever try to add a radial to get 80m as well? I had once a 40m loop with 2:1 balun plus 17m radial adding 3.5MHz. Opening the loop plus some tunig wire got me on 30m. This was a permanent installation not portable but was nice for 20 up to 80m without the need for a tuner.
73, Hermann OE1HFC


#6

In reply to OE1HFC:
Dear Hermann,

I doubt if this will solve your problem but the following links are relevant to the effects of static on summit activations.

http://groups.yahoo.com/group/Summits/message/4615
http://groups.yahoo.com/group/Summits/message/4621
http://groups.yahoo.com/group/Summits/message/4639
http://groups.yahoo.com/group/Summits/message/4661
http://groups.yahoo.com/group/Summits/message/4682

Grounding the antenna before it reaches the rig should shunt static but lightning conditions can sometimes follow and as you will know, grounding would then not give safety. The static damaged my rig and I found that even with the antenna grounded, the noise level still prevented signals being heard in most instances.

It’s good that you know how to protect yourself but I agree with Richard G3CWI, there is an element (and the chance of an escalation) of danger and to leave the summit is good advice.

73, John.
G4YSS


#7

In reply to G4YSS:
Dear John,

Thank you very much for links and related information, which describe what I observed and the known rules for personal safety. I was sure that experience about operating portable qrp at increased static discharge level must be with someone already. I appreciate the way you point out the experience as it will be to the benefit and safety of not only me but also to SOTA-interested and other fellows. I can confirm the observation of peaking static discharge just prior to start of rain, drizzel or snow fall, even out of blue sky. In winter I tried to erect a vertical on a summit in the snow, weather was fine, but stopped doing so after I got a shock with appr. 4m wire up. A short 6.8m wire average 1.5m up parallel to ground and a 10m radial allowed to qso without problems. The antenna was tied to the steel-made summit cross using nylon line and sloping down staying well away and below the cross. So the antenna was obviously not picking up noticable static discharge. Conditions might have changed as well. I did not try the vertical at the end of my operation to verify that.

73, Hermann OE1HFC


#8

In reply to OE1HFC:
Hermann,

40m but with the wires up in the air. Did you ever try to add a radial
to get 80m as well? I had once a 40m loop with 2:1 balun plus 17m
radial adding 3.5MHz. Opening the loop plus some tunig wire got me on
30m. This was a permanent installation not portable but was nice for
20 up to 80m without the need for a tuner.

I calculated the theoretical radiation pattern of the simplest loop I could imagine with EZNEC. The problem is that it is so close to ground that I was not really confident with the results. In EZNEC you can easily try different what-if-I-do-this cases. I tried also adding radials to the model. Now I can tune the loop to 80 m with a balun without radials, but otherwise have not had success working on this band. Probably the antenna should be twice bigger than the 40 m model. Or it is the day time D-layer as pointed out by G3CWI. The proximity of the ground is a big question mark. In loop community the general believe is however that the loops do not need as much height as the dipoles. For snow or rain statistic the loop is better.

Typical set up photo: http://sral.fi/oh7bf/Rodomont/photos/photo_13.html

Interesting info from G4YSS on the lightning strikes. Based on my one time experience I agree - better to avoid such situations.

73, Jaakko OH7BF/F5VGL