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HF antennas on short masts


#41

Hi Martin,
that link to ebay says the 5m mast is UKL58 plus UKL15 shipping - that’s expensive compared to the EURO 32 (+shipping) for the longer 6m mast from LambdaHalbe! I suppose if it’s stronger and lighter it may be worth the extra money.

I’ll be interested what you find with the caperlan mast at EURO 40 with free shipping it’s about the same price as LambdaHalbe (but it’s currently out of stock).

73 Ed.


#42

Hi Ed,

indeed, the DAM rod offer on ebay is a bit pricey. When I initially researched this rod, it was ca. 35 EUR + shipping from Germany. But then the delivery was delayed again and again with a final delivery promised for January. So I decided to cancel the order and buy it from the few suppliers who had it on stock, because I did not want to wait 2 - 3 months.

DECATHLON also has a 5 m version with very similar features for 30 EUR:

But by the time I found that I had already ordered the DAM one.

The real point I am trying to make, though, is that if the carbon fiber material has no significant effect on the performance of the antenna, then these masts are a huge improvement over the ones from lambdahalbe.de. They are about half the weight and 60 % the travel length.

73 de Martin, DK3IT


#43

Hi all,

attached, please find a picture that gives an impression of how much smaller the 5m DAM carbon pole is in comparison to the masts from lambdahalbe.de.

From top:

  1. 6m lambdahalbe, 603 g
  2. 5m lambdhalbe, 420 g
  3. 5m DAM Pocket Pole, 213 g

Of course the open question is how well the carbon fiber masts will work with vertical wire antennas. Theory tells us that we might face a couple of problems, at least one of the following:

  • The antenna wire might be coupled capacitively to the conductive mast, shifting the impedance and possible creating a shunt to ground if the mast is not properly insulated from ground.
  • RF might be reflected from the mast and cancel out RF from the antenna wire (in the sense of an “image antenna”).

Given the improvement in terms of weight and size, I am seriously interested in learning

a) how significant the effects are and
b) whether we can mitigate them.

For a), I plan to set up two identical wire antennas for 20m and attach them to two WSPRlite devices and measure the difference. I already did a few tests and got quite acceptable results. Without a systematic approach, however, they are not very useful.

On the Web, there is a wide range of opinions about carbon-fiber near antennas; many quadro-copter fans report problems with antennas behind or near carbon-fiber parts (but then again, they work at 2.4 GHz, and the materials used might be very different in terms of geometry and resin vs. carbon ratio etc.). Also, the rod elements are much thinner. Some hams report no problems except for a slight detuning.

Should the problems be significant, one could think of the following countermeasures:

1.Vary the distance between wire and mast, e.g. by attaching it close to the rod vs. using small spacers or sloping it slightly.
2. Insulating the lowest segment by adding a layer of shrink tube.
3. Connecting the rod to the wire electrically so that it becomes part of the radiator (but then again the question is how well the joints between the segments form an electric connection).

Any ideas and experiences will be very welcome!

73 de Martin, DK3IT


#44

Hi Martin,
as usual, a very deep and precise approach!

Sorry, I haven’t got any experience yet on Carbon fiber poles, but I’m planning to try one for my inverted Vee End fed half wave. I guess that such configuration wouldn’t produce any detuning at all!

If I can do further tests for a vertical I’ll give it a go and tell here.

Look forward your WSPRlite results, good luck!
73 de Ignacio


#45

Hi Martin,
Very interesting indeed. Looking forward to hearing from you.
73 Fabio


#46

IMHO, the perfect way to use these carbon masts is with end-fed antennas: anchor the end of the antenna wire to the pole at 1-2m height and run the wire out through some kind of loop attached to the top of the carbon pole. Bring the antenna wire away from the pole with a little tension, forcing the pole to bend into an arc. The wire will form an inverted vee shape and will be separated from the arc of the pole. Fred KT5X originally promoted this scheme because it fits in so well with his ultra-lightweight packing scheme and I tried to copy it with great results.

73, Barry N1EU


#47

Andy,

I have been using a link dipole (looks like an inverted vee) for all bands 40-6M, apex at 12 feet, since April of 2013 for SOTA. I have made over 9000 QSO’s, which includes Summit To Summit contacts with VK2, ZL, G, GW, S5, DL, HB9, KH6, KP4, and OE. Almost all QSO’s are QRP…a few running 25 watts or so (turns out the extra wattage is also not very important when using CW).

So, short story is that short dipoles work very well, and are easy to make and deploy.

Having said that, more antenna height is always better, but 3 db harder to deploy in the field.

Good luck!

73
Pete
WA7JTM


#48

Hi Barry,
that looks like an interesting approach - is there any link / image of this deployment style on the Web?

73 de Martin, DK3IT


#49

Pete, the ease of deployment very much depends on the summit flora. On heavily wooded/vegetated summits like we have in upstate NY, a single-ended (end-fed) antenna is much easier to deploy than a dipole.

Martin, I looked around and couldn’t find any photos. I’ll try and take a photo next time I’m out.

73, Barry N1EU


#50

You are correct Barry it does depend on the summit, and your forests are definitely thicker than those here in Arizona.

I guess all I am saying is that I have never let trees, or lack of any ground cover at all, get in the way of putting up a dipole and making contacts. The EFHW or the Dipole, in most any deployment will still work. Sometimes you just gotta dance with the one you took to the party.

73,

Pete/JTM


#51

Barry described my antenna set up perfectly! I also followed KT5X’s advice. The EFHW configuration has worked well for me both below the treeline and above. Several of the summits I’ve been on here in Colorado had a small operating area with cliffs on multiple sides The EFHW was easier to set up as I only had to deal with one direction when securing the longer wire.

73, Brad
WA6MM


#52

Hi Brad,
thanks - two questions remain:

  1. Do you use a resonant length or a random wire?
  2. Do you connect the antenna to the UNUN/ATU at the mast side or at the open end?

I am asking because my current love with vertical antennas is fueled by the fact that I need minimal space AND sit directly next to the mast. Both on summits with other mountaineers and casual lunch break operating from a park or so, it causes much less attention and trouble if the antenna only extends vertically. What I do not like so much about inverted vees is that there is really a large area where other people can run into your wires , causing them and me trouble.

73 de Martin, DK3IT


#53

By the way, it seems that HB9CZF uses a very similar approach as yours:

Martin


#54

Hi Martin,
Check out my qrz.com page and scroll down until you see the diagram on my antenna. My trapped EFHW antenna is resonant on 20,30 and 40m. The 81:1 matching unit is at the pole side about 5 ft off the ground and about 6 ft away from the pole.

73, Brad
WA6MM


#56

I agree with the observations that overall height is not all that important for a horizontal antenna. All 180 of my activations have been done with a 1" diameter- telescoping to 16’- carbon pole- cheap off Ebay- and a 20 meter dipole, fed with rg 174, tuned for other bands. I doubt hauling the great big poles up the hill would have helped me a bit and doubt much more power would have either, but would have given me more muscle mass. I also agree the EFHW is a much easier solution, but stubbornly cling to this original dipole till something breaks. Hasn’t yet.


#57

I guess I should have qualified- overall height not that important-- in the SOTA framework. Of course its important for a permanent setup.


#58

Hi all, the weather and the bad CONDX delay my true WSPR comparison of using the carbon-fiber rods for vertical antennas, but I still tried to continue my analysis. Here are my recent findings:

  1. The material has quite a high DC resistance: When measuring with a miliohm-meter, the resistance of one half circumference of the largest section gives 150 - 300 Ohms for ca 2 - 3 cm. There might be some contact resistance involved, but even additional pressure does not change that a lot, and the section I used to measure seems to exhibit the raw carbon-fiber without covering or resin surface.

The materials shown in the quadrocopter community videos on Youtube had values in the 1 - 10 Ohms range.

So it seems that the fishing rod materials use more resin or a different fiber arrangement or geometry.

I bet that many wet trees or bushes we have near our antennas have about the same DC resistance.

  1. I also checked wether the rods detune inductors. For that, I used the base loading coil from my SOTA vertical antenna design (actually a previous version). The inductance of ca 12 uH is almost unchanged when you insert the full, collapsed carbon-fiber fishing rod. It will be even less if only one hollow segment will be inside the coil.

A bit inconclusive is the observation that other objects from ferromagnetic materials also do not have a major influence on the inductance (I only tried steel, iron etc.).

However preliminary this is at this point, I expect that the further experiments will show that carbon-fiber rods are much more useful for SOTA antennas that we may assume, even for verticals.

Attached, please find a few pictures.

73 de Martin, DK3IT
Test Setup for Resistance:

Resistance DAM 5 m Rod

Resistance DECATHLON 6m Rod

Inductance of Coil Before Measurement

Almost no Change in Inductance


Telescoping Pole
#59

Hi Martin

Thank you for carrying out the tests, and sharing your results - interesting stuff.

Did you try to measure the resistance along the length of the pole, rather than around the circumference (over a length simillar to half the circumference)?
I don’t have one myself to test (yet) and know nothing of the structure, but I’m imagining longitudinal fibres to resist the strain of bending the pole…though it probably has layers in various orientations!

73
Adrian
G4AZS


#60

Hi Adrian, I did not yet do that, because the calibrated probes for my meter are too short for that. What I noticed is that the junctions between segments are likely rather well insulated, for there is an additional layer of resin at the top end of each section, so we will likely not have one long conductive element, but rather 11 or so of 30 - 40 cm length.

Martin


#61

My six ounce 18 ft ebay pole supports my #26 gauge teflon EFHW trapped wire. It collapses to 18 inches, something like fifteen dollars on ebay,. - fred kt5x (aka WS0TA)