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EFHW Dipole - Mono Band Version

Here is a picture of my 10m version used at Booroomba Rocks VK1/AC-026 (Dec 15)

The stub (L1) is folded back on (L2) and the common feed point fits inside a PL-259 used for RG-213.

This is a good view of the stub L1 and L2 side-by-side. (Dec 15)

73, Andrew VK1AD

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Hi Andrew,

excellent! A picture is worth a thousand words.

73, Roman - DL3TU

Hi Roman (et al),
Well I built my 20m version - no T-piece, just soldered together. Cost of parts €0,00 as I aready had a lngth of coax with a plug on one end and I have some really llightweght (24 AWG) PC boardpatching wire which I use for antenna projects.

The results on the Analyser after building to the dimensions from the spreadsheet -

Resonant freqency 14.285 MHz (as required by me for SSB operation),
SWR 1.42:1
IZI = 52.4 ohms
R = 49.4 ohms
X = -17.4 ohms
C = 634 pf.

Very impressive for an end-fed simply cut and soldered - no trimming at all was neccessary!

Now I just need to get it on a summit to test it out.

I suppose I should call my implementation a “Helical vertical” as I had to wind the wire around the 10m GFK mast a lot to make it fit in the height available - in fact the lower coax portion was half on the ground.

73 Ed.

Hi Ed,

I’m glad you achieved such good results at the first shot! Congrats :slight_smile:
From my experience it’s no problem if the coax is lying on the ground as it is supposed to carry no RF on the outer side of the shielding.

The only thing one may want to watch is the open end of the coax (where the antenna wire is connected). At this point the voltage reaches its maximum - almost 1 kV peak with 100 Watts. Some shrinking tube is recommended to protect this point against mud and moisture (as can bee seen in VK1AD’s photo).

Good luck with the new antenna,

73, Roman - DL3TU

Try this link https://web.archive.org/web/20150701035808/http://www.mods-ham.com/21_Rund%20um%20die%20Antenne/Rund%20um%20die%20Antenne%20Teil%207.pdf

The Archive knows all!

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Hi Roman - yes that point in the antenna is well insulated. I think with some closer winding of the open (but insulated) wire piece on the 10m fibreglass pole, I should be able to get more of the coax on the bottom of the pole.

Looking at perhaps gettng out to a summit with it tomorrow to test it out (Just EU though, I wont be getting up early enough for Long Path to VK).

73 Ed.

Thanks Bruce,
Looks like Web archive is like the “way back machine” site (or is this the same site perhaps?).

Great to get the PDF file. For those who can read German, this is a nice collection of descriptions of interesting antennas from Max Rüegger HB9ACC, well worth the read.

Once I am happy my 20m EFHW vertical works, I’ll build another one using the thin coax (adjusting lengths for the velocity factor of the cable) and that will then be a very lightweigth and compact antenna. It’s not bad with RG58 but given I only operate mostly QRP going to the thin lightweight coax (as long as I insulate the high voltage point well enough) should be a good move.

73 Ed.

Hi Bruce,

thanks a lot for digging out that link! The antenna handbook of HB9ACC is definitely worth reading.

73, Roman - DL3TU

BEWARE OF BETTER QUALITY COAX!

Having had such success with my first attempt, I decided to produce a lighter version using RG-174 coax rather than the RG-58. Well RG-174 has the same velocity factor as the RG-58, so I cut the same lengths and built the antenna. when I tested it though … best SWR 2.2:1 way out of the top of the 20m band!

Checked the connections - all OK. Then I looked at a different site for velocity factors to find that the lower loss, higher frequency, more expensive foam version of RG-174 has a VF of 0.735 not 0.66. What this means is that I cut the coax lengths too short! “RATS” or words to that effect!

Lets see if I can fix this as the RG-174 version is really easy to pack. I have even added a golden link conector on the end of the coax and the insulated wire section (which winds onto an advertsing gift - YoYo ) to enable easier handling.

(the clip, simply clips to the top of the mast).

Ed.

UPDATE: In the end, with a lot of help from Roman, I found the real problem. The coax which I thought was RG-174 was actually 75 ohm RG-179. Not that the fact that it is 75 ohms rather than 50 ohms is the problem. The problem is that the Velocity factor of the coax is 0.70 not 0.66 (PVC RG-174 coax) or 0.735 (foam RG-174 coax) and of course with the wrong velocity factor the lengths from the calulator spreadsheet were wrong.
After length correction my (now 15 metre J-Pole) made 4 contacts into North America on Tuesday from DL/BE-093 with just 5 watts of SSB, so the antenna works very well and it’s great that it can be packed away so small!

Hi Ed,

Most problems with antennas are caused by the builder making “improvements” and not making due adjustment. So your experience with the foam dielectric wasn’t unique in the field of antennas but well worth pointing out so others don’t make the same mistake.

I tried to make a 2 m version but it didn’t give an acceptable match. I suspected it was because the half wave radiator section did not have the assumed feed resistance. I got improved, but still not good enough, results by changing the radiator for a thinner wire. Should be able to fix that by adjusting the coax tapping point.

So not only do you need to check the VF and adjust the coax sections, you may need to experiment with the radiator.

For HF the radiator is electrically thinner and so is closer to the assumed resistance, hence the cut and play results reported.

73
Ron
VK3AFW

www.hb9f.ch is an alternative I found the other day.

You still need need to able to read German. Google complains the page is too large to do it for you.

73

Andrew

Hi Ron,
I was surprised with my first (RG-58) construction that ZERO “cut and play” was required. I was expecting to have to change it but in fact it was exactly resonant by simply using the values from the calculator. I have now “repaired” the RG-174 version, and will try to test it today, now that I have put the correct VF into the calculator.

73 Ed.

For a discussion in English, see this preso: http://audiosystemsgroup.com/VerticalDipole.pdf

This design is common for commercial VHF antennas. There, you’ll see a larger diameter rigid bottom element with the coax running through it. They are easy to spot. There are no radials and the “skinny top, fat bottom” elements are distinctive once you recognize the design.

Using a separate sleeve avoids the tradeoff between a resonant length element and a 1/4 wave section. Thanks to coax velocity factor, you can’t get both lengths correct with one length of coax.

These are sometimes called a “sleeve dipole” or “coaxial dipole”. There doesn’t seem to be an agreed-upon name for the design.

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Hi Walter,
Another interesting antenna - but not the EFHW Dipole(J-Pole) that this thread is about - I think this piece would be better for the discussion going on in another current thread on lighweight antennas - here:

Sorry, I misread the original article.

The sleeve dipole should be better in nearly all respects. Shorter, slightly lighter-weight, and less loss in the 1/4 wave section. The J-pole version is a 1/2 wave of wire plus the 1/4 wave of coax. The sleeve dipole is 1/4 wave of wire plus the 1/4 wave of coax. Since it is a 70 Ohm antenna, coax losses should be minimal.

wunder

I use a resonant end fed half wave on 20m from gwhip antennas. It fits on my 10m pole as a slight sloper. I’ve had a couple Americans on it whilst I’m on a summit with around 25w. Seems to work well.
Bit heavy for some people as it’s around 950g with its tuned circuut box on the bottom.

Great input Walter.

I wonder if we could arrange a regional antenna test, to compare all the various vertical antenna options - using the same location and same RX/TX equipment?

I have read that the J-Pole loses 50% of it’s signal because of its use of the stub to match the feed impedance - as you say the sleeve dipole coould be a lot better in this respect.

Oops, now I should have posted this to the other thread!

Ed.

Oops, the choke adds weight for the sleeve dipole, so it might not be lighter. But they are both vertical half wave radiators, so the performance should be very similar.

100g for my J-pole made with RG-179 coax and 24 awg insulated wire.

In theory OK for up to 200watts (but certainly OK for 25w).

Ed.

After sorting out why my lengths were not as expected (I was using RG-179 coax not RG-174 as I had thought) I have built three J-Poles that are resonant on 15, 17 & 20 metres … “but wait there’s more”.

Following some very annoying occurrences of the DX-Wire 10m mini-mast collapsing on me and it being too heavy, I set my self a “Scope of requirements” list which included using the 6 metre Lambdahalbe mast not the DX-Wire one (the 6m mast is less than half the weight of the 10m mast and shorter to carry). By winding the wire around the mast, it is possible to fit either the 15m or 17m antennas onto the mast. the 20m J-Pole insulated wire element however is too long to fit on the mast. In all three antennas I built the coax feed and stub / T-junction separate from the wire element and have 2mm gold plated RC battery connectors in between to connect them. This was initially done to make packing and assembly / disassembly easier as I can simply coil the coax part and the wire part winds onto a small former.

What to do about the 20m antenna? Perhaps I can run off the excess length from the top of the mast, Inverted-L like and guy it down on a thin cord at a distance? This would be one solution but another idea struck me - why not simply run the excess out at the bottom of the mast at about 1.5 metres high, over onto a walking pole or similar?

This antennas design is single band. the coax assembly is different for each band as is the insulated wire element, however I then looked at what I was thinking of doing for 20 metres and thought well I can do that for 17 metres as well and then just leave the 15m element on the mast and plug in extra lengths of wire element for the other two bands when needed. The major advantage of this approach is that I don’t have to take down the mast, coil-up the antenna and then put the mast up again with a different wire element, every time I want to change bands. Switching the coax assembly for each band is simple as I have theses as separate modules in any case.

The question was, would this 15m plus 17m or 20m extension actually work in practice - electrically apart from the extra connector it should look the same.

Today, I tried this solution and here are the resulting readings from my antenna analyser (sorry for the reflections):


15 metres - 21.285MHz 1.08:1 SWR

17 metres - 18.010 MHz 1.09:1 SWR (a small adjustment still needed on length to bring frequency up)

20 metres - 14.285 MHz 1.15:1 SWR

So you can see, it appears to work and … I have reduced the weight in the process,
Parts now to be packed -
3 RG-174 coax assemblies with short feed cable
1 extension BNC-BNC cable from short link to rig or amplifier.
1 half wave 21MHz insulated 24AWG element
1 short 24 AWG extension for 18MHz
1 short 24 AWG extension for 14 MHz.
and of course the LambdaHalbe 6m portable mast.

Now to try it out on a summit!

73 Ed.