In reply to GW7AAV:
One possible answer that might work would be to wrap the balun on a short section of plastic pipe similar to the size of the boom and slide it vertically onto the sotapole immediately below the beam. It would find it’s own size and lock on the taper of the pole just under the beam and would have the effect of taking the weight of the croc clips at the feed point.
73 Mike
In reply to 2E0KPO:
Just one other proposition Steve is Sotabeams new Rucksack special, which looks a very tasty and reasonably priced piece of kit.
http://www.sotabeams.co.uk/RSS.htm
73 Mike
Re the SOTA Beam - I’ve found there’s no need to do any more than use a reuseable tiewrap to take the weight of the coax running down the mast. Richard suggests two on the pole - I find it much easier to strap the cable to the boom with a single tiewrap - the coax then hangs down parallel to the mast. The piece of coax and balun between the tiewrap and the croc clips doesn’t weigh enough to affect the grip of the clips onto the elements, even in gusty wind.
As for the new 1/2 wave - it will certainly do the business and the price is very reasonable. Pity it’s vertically polarised!
73, Gerald
Sotabeams new Rucksack special
I have a ‘first run’ example of this new product, and will be using it on my ascents/descents at the weekend, commencing Saturday morning. Contacts while I am pedestrian mobile would be most welcome; let’s see how this antenna shapes up.
Tom M1EYP
Note - we can make this product to order to work on other radio frequencies (Emergency Services, Mountain Rescue, Ranger Service etc).
Maybe Richard might like to clarify this a little by saying VHF/UHF frequencies or can I order one for top band? Now there’s a challenge! ;o)
Good luck with the new product Richard.
Steve GW7AAV
PS Mike GW0DSP - That seems like the best idea as to what to do with the balun. Spot on!
In reply to GW0DSP:
One possible answer that might work would be to wrap the balun on a
short section of plastic pipe similar to the size of the boom and
slide it vertically onto the sotapole immediately below the beam. It
would find it’s own size and lock on the taper of the pole just under
the beam and would have the effect of taking the weight of the croc
clips at the feed point.
Brilliant Mike! Wish I’d thought of that! A practical point - the pipe used as a former would need to be a slightly larger inside diameter than the outside diameter of the SOTAbeam so that it would fit under the beam. Perhaps a length of 25mm MDPE water pipe, or 25mm conduit.
73 de Paul G4MD
In reply to many:
You guys do like doing things the hard way. If you want a balun that doesn’t weigh much and get in the way, then make a bazooka or sleeve balun.
You can make one out of the outer shielding from a piece of coax. For 2m, you need about 13.5in of outer braiding. Removed a small amount of the outer sheath of your coax, 14in from the end, to expose the coax’s outer conductor. Slide the extra braiding over the coax and solder the end of the braiding to the coax outer. Do this carefully so you don’t melt the coax and get a short circuit. If you take a piece of braiding much longer than you need you can slide it over and bunch it up to give an almost solid covering. Don’t forget you are sliding it over the outer sheeth which is fatter hence the extra length needed. Trim so only 13.5in is covered. The end nearest your croc clips is not connected. Then cover the whole contraption with some heatshrink. This will hold the sleeve balun in place and waterproof the exposed soldered joint.
Adds almost no weight to the coax and is still flexible etc. and easy to manage. If it takes you more than 30minutes then you’re doing something wrong!
To calculate the exact length of braid needed the formula 7500/F * Vf is used. F is the frequency in MHz, and Vf is the velocity factor. So if the Vf is 0.66 and F is 145 then the length is 34.1cm or 13.4in. Make sure you go far enough back from the open end to fit your balun on.
Andy
MM0FMF
In reply to MM0FMF:
Nice idea Andy, using the RG58 braid would give a snugger fit than my RG213 method.
Have you ever tried testing the frequency of the balun? I’ve tried using a GDO but not had much success; there must be other ways!
73 de Paul G4MD
In reply to G4MD:
Have you ever tried testing the frequency of the balun?
No I haven’t but I’m happy that the formula is more than accurate. You really only need to know the velocity factor of the coax you are using. You can find that from the web if you don’t know it. If you work out the change in length of the balun between 144 and 146MHz then it’s only 1% of the overall length. So I’d cut for 145 and be done with worrying. My 9 and 13 ele 2m Tonna beams both used a fixed size sleeve baluns and had much more than acceptable performance over the whole band.
You could always leave the last 2cm uncovered from heatshrink and stretch and squeeze it to size if you were concerned enough. I’d tin the edge so the braid doesn’t unravel with the vigours of use on hilltops!
Andy
MM0FMF
In reply to MM0FMF:
You really only need to know the velocity factor of the coax you are
using.
Hi Andy
Unfortunately, I have a feeling that the velocity factor for the balun sleeve will be a function of the thickness and dielectric constant of the outer insulating covering of the inner coax, rather than that of the coax itself, so is a bit indeterminate - hence my seemingly insane desire to be measuring the frequency…
73 de Paul G4MD
(Apologies to all for hijacking the reflector with my technical esoterica - I’ll crawl off back into my cupboard again now)
In reply to GW0DSP:
“Rucksack Special” Great idea but a bit late now, stuff is on its way to me from Sandpiper… Oh well…
In reply to G4MD:
I have a feeling that the velocity factor for the balun sleeve will be a
function of the thickness and dielectric constant of the outer insulating
covering of the inner coax
Well spotted. For PVC it’s 0.53. You just need to rerun that calculation with the new value. Although having done some more reading on sleeve baluns, PVC is possibly the worst material to use 
Andy
MM0FMF