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Author Topic: A vertical dipole for 11 meters (CB)  (Read 231 times)

Offline ChrisSmolinski

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A vertical dipole for 11 meters (CB)
« on: February 15, 2021, 2059 UTC »
I've had a horizontal dipole for the 11m band (about 50 or 60 ft high) for some time now, it works well for DX, but I thought perhaps not as well for more close in / local reception, which would tend to be vertically polarized.

I debated a bit as to what kind of antenna to set up, a ground plane, j-pole, or vertical dipole were the top three choices I came up with.  Some research online quickly eliminated the j-pole, as it is a problematic antenna that often does not live up to the hype. That left the ground plane and vertical dipole. A ground plane antenna is nothing more than half a dipole with the ground plane acting to provide the missing element via a mirror, yet more complicated to build. So that left the vertically oriented dipole.

The next question was whether to make a folded dipole out of 300 ohm ladder line / twin lead (which is what my horizontal 11m dipole is made from, and fed with a 4:1 transformer, as is my 43mb dipole) or just a regular dipole. I ordered the 300 ohm line, but then pondered it a bit, and after some discussions with Radio GaGa, decided to go with regular wire, both for ease of construction as well as not having to wait for the 300 ohm line to arrive (hey, anyone want to buy some 300 ohm line??)

Being cheap, I looked around for some scraps of wire, and found I had two lengths of #10 insulated stranded wire that were long enough. The nice thing about the 11m band is that wavelengths are short enough that scraps of wire are all you need. I cut each wire 8 ft 7 inches, plus a little extra to go around the insulator on each end (I stripped the insulation off that part so that I could wrap it around the wire and both hold it in place as well as short out, so as to not make the wire longer than needed).

For the feedpoint I made a custom version of one of my Cyclops transformers ( https://www.blackcatsystems.com/rf-products/cyclops_rf_ham_shortwave_radio_matching_transformer.html ), with a 1:1 turns ratio, as the feedpoint of a half wave dipole is about 70 ohms at resonance (insert hand waving to ignore the effect of the ground on impedance) and I'm feeding it with 75 ohm RG-6 coax.

I installed it this morning, and am pleased so far. It does seem to be more sensitive for the local & semi local stations vs the horizontal dipole. I ran both antennas for a while on two different but comparable SDRs, with the audio from one going out the left speaker and the other out the right.

I notice it picks up less RFI than the horizontal dipole, but that could just be due to where in the yard it is located. The feedpoint is at about a 35 ft height, I used an existing rope I had in a tree as the weather really isn't conducive to getting out the Big Shot to launch another rope higher.  Once the weather improves I may do that and see if I notice any favorable difference. Additional height should improve line of sight reception, but OTOH the takeoff angle portion of the radiation pattern is dependent on the height, and a higher antenna is not always better from that point of view.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 300 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline ~SIGINT~

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Re: A vertical dipole for 11 meters (CB)
« Reply #1 on: February 16, 2021, 0102 UTC »
Hello Chris,

The folded dipole is probably not a good idea. I spent last summer & fall building some experimental antennae, one of which was a folded dipole. It turned out to be a disaster. For some reason, I ended up with some deep nulls at certain frequencies (very high VSWR) rendering the antenna useless in those bands. It was deaf. Somewhere I have a screen shot of the VNA to prove it. In the bands where the antenna did resonate it worked ok. In the end, I ended up dismantling the "folded half" and converted that antenna to a 42 ft end-fed long wire. It is 15 ft off the ground and horizontal. This configuration works well. I experimented with both hight and tilt (slopping) and the optimum results were to have the antenna as low to the ground as practical and as horizontally flat as possible. The end-fed is a keeper. The only modification that I am contemplating is that this summer I am going to change out the UNUN transformer for a higher impedance one and try to add a short counterpoise. The counterpoise will supplement having to depend on the coax shield for that function.

There is a noticeable difference between my end-fed and my Barker & Williamson which is setup in a slopped configuration. For example, when I was listening to Radio Free Whatever last evening, as conditions changed, I started to loose the station using the B&W. I switched to the end-fed and was back to a +10 solid signal. I have been trying to model the antennae using MMANA to determine the take-off angles but I am struggling with the software. A work in progress.

One of the best verticals that I have operated is a Shakespeare HF 120 series antenna. I had mine in service for over 20 years and only recently took it down this past fall to make way for my Wellbrook loop. I am contemplating putting the 120 back up but running scarce on antenna farm real-estate. Between the B&W, the end-fed, the UHF SATCOM, the VHF/UHF stick, the discone and ADS-B antennae I am tight for space, not to mention trying to squeeze even more coax through the wall. The second antenna I have for close contact work is my Harris 1936 / 1938 NVIS antenna. It is ideal because it is an NIVS antenna, but again, requires real-estate to erect. I can achieve NVIS with the HF 120 as well by using the 4282 tilt whip adaptor but that is scary when the whip is at 20+ feet off the ground.

Richard

Offline RobRich

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Re: A vertical dipole for 11 meters (CB)
« Reply #2 on: February 16, 2021, 0145 UTC »
I have had a couple of Shakespeare 318GBT 18' verticals over the years. Basically an end-fed 18' vertical for 12-10m operation. It likely would suffice for 17m and even 15m at reduced efficiency with ground radials and a tuner.

First one was during active production of the antenna back when I was in the TN mountains. It lasted through many years of abuse. Mounted at like 10'-15' height. No radials. Basically just coiled the leftover coax. The metal mast and ground were probably acting as a counterpoise. Worked lots of 11m DX from a few watts to.... well, an export radio driving a solid state amp driving a tube amp. o.0 Yeah, that was a long time ago. Anyway.

I wanted to put up something for upper-HF after relocating to FL. Found a new-old-stock 318GBT on eBay for a decent price. Easy decision IMO. It has been deployed for years. It is ground mounted over eight 9' surface radials and using a MFJ-915 1:1 "rf isolator" near the feedpoint. The tuning coil can quickly sort out the matching difference when adding a few short radials. Not that I really care too much, as it is more of a receiving antenna these days. I have a couple of CB mobiles collecting dust, assuming they still work. Suppose I should check them.

I have a new-in-box Antron 99 (actually a RS clone IIRC) floating around here somewhere as well. Internal construction quality can be YMMV, but otherwise I find the admittedly not-so-sophisticated A99 design still can be a decent performing 12-10m vertical for the money if properly working and deployed correctly, and more so if you can find one for little money at a yard sale, hamfest, junk store, or similar. ;)

TLDR? Assuming one is not dealing with massive man-made RFI, verticals can and do work if willing to spend a little time on the planning and installation, especially for those of us with limited space for an antenna farm.
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Offline ThaDood

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Re: A vertical dipole for 11 meters (CB)
« Reply #3 on: February 16, 2021, 0744 UTC »
Anyone remember the Big Stick from the 70's to the 90's? I had one in 1992 and locally it talked about 10 miles around. Granted, I was just under 15ft off the ground with it. However, in April of that year, 11M DX exploded from Europe and Asia. France, UK, Spain, Germany, with just a few watts in the afternoons. And, daily QSO's with a friend in Texas. Yeah, that was a great skip talking antenna for 11M, the best that I ever had, looking back on it. When you look at the design of what the Big Stick was, it was a coaxial antenna, or a modified Dipole, really. So, my guess would be that a matched VERT Dipole will hear stuff locally from about 20 miles, depending on antenna height, but should be a damn good Sporadic "E" and F2 antenna when the propagation comes around again. Oh yeah!!!! In 1999, I made a VERT 11M Dipole from a 102" whip, with 106" of cobbed dehumidifier aluminum coil straightened out, for a radial. It talked to mobile stations 20 miles out, and it too heard some nice skip. I think that was the antenna that I DX'ed the Hamburg, Germany 10M FM repeater on 29.690-/R, hitting me at S20/9. I also DX'ed a 10M AM QSO on 29.000MHz from an East German working a dude in Utah off a whip from the Soviet Military. I heard both stations over S9. Damn, I miss those conditions. But, there ya go... Possibilities of what might be possible with a Dipole VERT on 11M. It will DX down to 20M nicely too and hear 6M stations as well. 
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Offline Brian

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Re: A vertical dipole for 11 meters (CB)
« Reply #4 on: February 16, 2021, 1704 UTC »
I had a vertical and ground plane for CB. Set it up last summer for DX, no local activity here.  It was mounted on the ground using my MW ground radials. Very noisy. I had better success using my 32 mtr Inv V dipole. 

Offline jas340

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Re: A vertical dipole for 11 meters (CB)
« Reply #5 on: February 28, 2021, 0053 UTC »
If buying off the shelf I would go with the Sirio gainmaster. It is very quiet. Imax 2000 as second choice. Mount on a 10ft mast that will sway in the wind so the antenna does not take all the wind loading.

Offline Σ

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Re: A vertical dipole for 11 meters (CB)
« Reply #6 on: February 28, 2021, 1433 UTC »
I had a Shakespeare Big Stick back in the early 80s. Also had an Astroplane that did well. Got some Astroplane copies in storage that I should assemble and check out. Too bad there isn't more local activity here... almost zero including Ch 19 traffic from the highway only a mile away. Once in a while I will hear a couple of vehicles passing through but that's it.

I also miss those international DX conditions.
- Rob

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