In my SOTA kit I also have two different lenght 300ohm ladder line pieces.
I think this is good way to ensure tuning. The extension is easy to snap to the line with “sugar cube” like connector. I have soldered short pieces of one-piece copper wire to the ladder line ends. In my opinion it makes using the line much more convenient.
Like so:
Extension wire on the left. Please note that I also used hot-glue to impove reliability of the connection piece.
Regardin the attenuation. I am using 450 ohm ladder line in my home QTH on two separat antennas. Last winter one of my support rope snapped and the ladder line was laying on the roof in the snow. I did not make exact measurements of the attenuation but based on the S-meter the attenuation was around 15-20dB. The length of the ladder line piece in the wet snow was about 7 meters.
I always have support ropes available to lift the ladder line from the ground. I think this should be the recommended practice.
The lesson from that article is that even for a 60-foot (18.29 metres) run the losses from lying the ladder line on paving slabs or damp soil, or having it thoroughly wetted, run effectively at less than half an S-point. Since we are unlikely to set up with more than a few metres of ladder line lying on the ground then we can safely ignore the loss.
We know nothing about what kind of soil was involved in the experiment so it is best to assume that it was a loam with moderate organic content. I would expect a highly organic acid soil would give greater losses. Similarly, I would expect paving slabs to approximate to a limestone or granite rock surface. Many volcanic rocks (and some plutonic and hypabyssal rocks) have a significant content of metallic sulphides and would likely give greater losses. As a rule of thumb, if the rocks of the summit affect a compass then it would be better to suspend the feeder above them. If the summit is mantled in peat or has puddles of water then suspend the feeder, otherwise, don’t bother about it. We do have summits in the UK that affect compasses, by the way, and not just in the Cuillin of Skye, so don’t assume that this is a remote possibility!
Guessing that you missed the conclusions of the article. “Laying the ladderline in contact with the ground produced high losses and large reductions in the Velocity Factor - results similar to those reported by W1ZR.”
No, Richard, I drew my own conclusions from the data offered in the article - a loss of 2.56 dB at 24.92 MHz for a 60-foot length lying in contact with the paving, and a loss of 2.91 dB for the same length lying in contact with damp soil at 26.16 MHz. Assuming that the loss for a shorter length in contact with these materials would be proportionately less, and that for SOTA purposes no more than a few metres would be in contact with the ground, my conclusions given above were fully justified.
What’s more interesting is the way the loss shoots up when thoroughly wet. This seems to suggest use of this kind of feeder is not ideal for Scottish summits!
I use 300 ohm window for my G5RV doublet here and the tuning always changes when it starts to rain, so it is not just Scottish summits! I have it in mind to change to the traditional open wire feeder at some point in the future once I have solved a routing problem. Nevertheless, a loss of half an S point in a 60-foot length of wet feeder suggests that the short length likely to be used on a summit will not be a problem when wet…OTOH my run here is over 100 feet.
If I’m reading those tables correctly, he shows 6 to 8dB loss for 60ft of thoroughly wet ladder line. 60ft is just over 18m. My RG174 feeder now is about 10m. 5m to run up the pole and 5m to run from the base of the pole to where I’m located. So with my length of RG174 replaced with balanced feeder I’d be seeing 3 to 4db loss.
I don’t operate in rain, especially like the rain falling now. But I do operate when in cloud and mist. In those conditions everything gets thoroughly drenched. My interest in using a balanced feeder is several fold. One, because I’ve never tried it before and experimentation is key, in my view, to having greater radio fun. Two, to produce an all band antenna with a balanced ATU that weighs less (or rather no more) than the current dipole and feeder.
3db is only 1/2 an S-point. But 3dB is half the signal. When you only have 4.5W to start with, losing 2.25W in the feeder seems a very bad proposition. The current LF antennas are fed with RG-174 and then 10m length at the highest frequency used (10MHz) is 1.1dB. So on a summit in the clag, I’d see 3 times the loss straight off. But on a good day half of the loss than with RG-174. Of course I’d only need 1 antenna instead of 3 wire antennas carried now.
The obvious thing is to make one and an balanced ATU and try it out to see how it compares with full size resonant dipoles on LF and if it’s better than the inverted L for 20/17/15 and the 1/4GP for 12m. I’d probably make the feeder about 7m with an extension piece if I couldn’t end up comfortable beneath the antenna.
The high losses that you refer to were for feeder soaked with water containing a wetting agent intended to simulate an old feeder that had lost its water shedding properties. New feeder gave the much lower figures that I quoted. Its also noticable that the figures for 450 ohm feeder were more favourable. OTOH I often used to think that Highland rain contained wetting agent!
A tuner that I can recommend is the Z-match, I made the light-weight low power version here:
users.tpg.com.au/users/ldbutler/ToroidalCoreZ.htm
Mine is a bit heavier than it need be because I used minature airspaced tuning capacitors. It seems to match almost anything!
73
Brian G8ADD
PS The 6-turn secondary is a bit big for the HF bands and I found 4 turns worked better.
I use a link dipole fed with 10m of figure of 8 loudspeaker wire from MotorWorld.
At the rig end I have a small 1:1 balun. I don’t need an ATU on the bands the dipole is cut for (and a few more by happy coincidence) so very rarely carry one up the hills. The impedance of the speaker wire is allegedly about 75 ohms.
I switched from using RG-174 after having trouble with RF getting in to the microphone of the FT-817. No doubt the radiation pattern is also improved.
I use this set-up with the FT-817 and very occasionally a small HFPacker 25W amp, on CW and SSB. It’s very light and compact.
I leave the excess feeder on the ground and have never noticed any ill effects or any difference if it’s stretched out. If there’s no support for the fishing pole, I sometimes make a ‘tripod’ arrangement with the 2 legs of the dipole and the feeder equally spaced in a circle so the antenna is self-supporting (tnx Richard G3CWI’s YouTube video).
Assuming that the loss for a shorter length in contact with these materials would be
proportionately less…
I agree with most of your conclusions on the practicalities Brian, but I’m not sure that the loss would be proportional to the length. I would guess that loss is greatest at voltage nodes. The measurements were taken on a mismatched line, and I picture the “wet” as a fairly high value shunt resistor capacitively coupled to both conductors through the plastic insulation…
So the loss in practice would depend on how closely the feeder was matched, and then which bit of the feeder was lying on the ground - it should still be less than the figures for a 60ft length, though, and could be considerably less…
Pure conjecture on my part!
as I understand it the only real advantage to using twin feeder going one each to the limbs of your dipole is that a balanced tuner will be able to load the set up on any band.
if you coil up your coax round a plastic po bottle size four or five turns you will impede then waves on the braid reaching the rig and hence reduce the standing waves caused by them mixing with the tax.
My approach to amateur radio has always started with “what is available, and how can I use it” rather than “what is the best solution, and what do I need to buy”.
I had a choice between RG58 coax, which is relatively heavy and bulky, or figure of 8 speaker wire which is less so.
Physical advantage of the speaker wire is that I just split a length to form the dipole, and then put 4mm wonder plugs on the other ends. No joints, and easy to spot an open or short circuit, and repair it with minimal tools in the field.
I don’t use a balanced tuner, just a coax to wonder plug adaptor - for which I carry a spare.
I would take far more care over a home station antenna, or if I was contesting, but simplicity is a big plus in the context of my activations, where anything more than four contacts is a pleasant bonus.
Achieving technical excellence is very satisfying, but then so is just making something work, even if it is more by luck than judgement!
“if you coil up your coax round a plastic pop bottle size four or five turns you will impede then waves on the braid reaching the rig”
Hi Carl
Your solution will only work effectively under rather specific circumstances I’m afraid. You might get lucky but a more rigorous approach will almost always be much better, as my measurements reveal:
Just saw this thread and must answer as I have done much portable work with balanced line - I have come completely full circle as well!
450 ohm line works incredibly well with balanced antennas and balanced tuners like the BLT, but it’s a pain to carry and much too heavy to hang from a light pole. If you have a tree support, it will let you run efficient antennas like a 40M dipole on several bands - 40, 30, 20, 17, 15, etc. Here in Colorado it’s often very dry, so as long as the line is supported off the ground by being tied up, or lifted by a dry tree limb, it’s easy to deal with excess. Its characteristics do change when it’s wet, but often not a problem with a tuner.
I have various lengths of 450 ohm line that are neatly fitted with banana plugs and jacks, so they can be plugged together to form different lengths - balanced extension cables! This is the best way to create the length you need for your site, and also to control standing waves, so your tuner can have an easy match. Sometimes just adding 2 feet can make all the difference!
300 ohm low-loss TV line is a good product for resonant antennas - it handles well and is lighter than 450 ohm line. Its losses are excessive for antennas with bad mismatches - such as a 40M dipole running on 14 MHz. I believe it performs better than RG-174 and PVC speaker wire, but it’s too heavy for a light pole.
I have a 20M dipole made of #22 teflon wire. Each side is 16.5 feet, about 5M. The wire is knotted at the center, and then about 25 feet of wire from each side are twisted together to form a low-Z balanced feeder - impedance perhaps 100 ohms - that goes to the balanced tuner and the rig. In practice a balanced tuner is not required if the antenna is used near low-Z resonance. On 20M this dipole works great, hung at 18 feet on a summit. On other bands it ranges from fair to rotten - even with a good tuner. Nevertheless, the loss in the twisted teflon is probably lower than RG-174 and similar coax, as well as the more lossy PVC products like speaker wire, computer ribbon, zip cord, etc. A tuner is still needed with the twisted teflon on 20M, because the feed is not 50 ohms - but the SWR/mismatch is relatively minor, so the tuner doesn’t have to do a major transformation. The tuner can be simple, and the losses low - at least on whatever frequency the dipole is cut for.
On windy or hostile summits, dipoles are more difficult to erect than end-fed wires like the EFHW. Even though I did many contact-rich SOTA activations with my 20M teflon dipole, I found that the EFHW and similar inverted-L antennas perform just as well on summits, and they are much easier to deal with in the bushes, rocks, and wind. Stringing two ends of a single wire is easier than dealing with two dipole wires plus a feedline! I’ve gone over to #24 teflon, which behaves well on the pole and has less wind load than larger wire. A 66 foot wire has a high-Z resonance in 40M, 20M, and 15M, and the patterns are effective. Usually I set up under the pole, feed the wire that comes down from the pole tip, and tie off the far end with thin dacron line, as high as I can get it. Often I tie the far end up on a high rock or tree - seems to improve results. The key to using the high-Z end-fed antennas is to use an efficient resonant high-Z step up tuner, based on a powdered iron toroid. Ferrite devices also work, but they are not as efficient, especially over several bands. No radials or counterpoise wires are needed or even desirable, as the capacitance to ground of the gear and operator takes care of the return current, when the feed is at 1000 to 4000 ohms. These systems are not fussy or tricky - you just have to keep your hands away from the high-Z feed, keep it off the ground, etc. The antenna can be whipping around in the wind, and as long as the feed end is secured with a single dacron string to a rock, the feed Z scarcely varies! The feed wire may be brought down directly from the bent pole tip - there is no need to string it along the pole. The pole can usually be erected without guys - just stick it in a small tree, or brace it with rocks on a high-altitude summit. The antenna itself provides enough tension to make it behave under normal conditions.
In addition, the single end-fed wire can be used as a low Z antenna (like a 1/4 wave inverted L), if fed on a frequency for which it is resonant - then you need at least one radial, about 1/4 wave long. A single end-fed wire, with no coax or balanced feedline, can be used effectively on many bands, resulting in a simpler and lighter activation with great results. A smaller and lighter pole can be carried, and then higher and more difficult peaks can be climbed, etc.
So I’ve come full circle, from using 450 ohm line on backpacking trips into the wilderness, to SOTA activations with almost no feedline. Now the only coax I carry is a 1-foot jumper from my ATS-3B to my tuner. The only balanced line is a 1-foot twisted teflon line from my balanced tuner to my high-Z step-up unit. Before long I’ll integrate more of the rig and get rid of one or both of these lines also.
I don’t think single wires care much if they’re wet or dry.
My own antenna modelling work suggests that we need to feed a dipole up high with balanced feed, etc., for best performance. However, it just isn’t worth the hassle and weight for activating a windy summit at 4000M, or higher, where there are no trees and often little time to mess with various wires and guy lines. Out here I’m getting dozens of contacts on multiple bands with my tiny ATS-3B radio. Sometimes I even work G and EU stations with my end-fed wires! I don’t know why I would carry feedline up a really high summit ever again!
Fred (KT5X aka WS0TA) has taken these concepts to extreme and reduced his entire SOTA station to less than 1 pound, pole included. I’m still carrying a few pounds, but feedline is one of the first things to leave at home when activating up where the air is thin.
