C-Pole antenna

630m (472 kHz) - 10 m (29 MHz) antennas, propagation, operating, etc

C-Pole antenna

Postby VK2FAK » Wed Jul 25, 2012 2:27 pm

Hi all...

I am thinking of having a play with one of these antennas soon. Its only a 1 band antenna but looks very simple, compact, can be built lite and is not to tall for a vertical.....The band I will make it for is probably 17m....

Has anyone ever tried one of these antenna, they never seemed to be to popular but hey,,,,I will see for myself....first hand....

John
VK2FAK
Forum Diehard
 
Posts: 972
Joined: Thu Apr 15, 2010 6:28 pm

Re: C-Pole antenna

Postby VK2AVR » Wed Jul 25, 2012 4:14 pm

I found these antennas while searching for something that could work from a 3rd floor (top floor) unit using a squid pole. Since they don't need a ground plane and can be supported by a single post (squid pole) they are an attractive concept.

With a bit more effort, balanced feeder and an ATU you can apparently make a multiband H pole as well
http://www.qsl.net/hb9mtn/hb9mtn_h-pole.html

although I do wonder, if it is acting as an "off centre fed" antenna are the feedline currents unequal? Many have cautioned against feeding an OCF dipole with ladder line because of feedline radiation, I wonder if it's also the case with this antenna.

I would be interested to see if a more compact H-pole could be built that works using a 7m squid pole on 40m-10m. I'm willing to forego 80m if it gives me a workable option, will have to get around to buying EZNEC one of these days (the website has an eznec model file for C pole and H pole). To properly analyse these antennas you should really include the feedline in the model, as feedline radiation and RFI are just as important as whether it radiates well. Of course, field tests are definitive rather than relying on EZNEC (which will have difficulty working with the feedline as it doesn't model close spaced wires well).

Geoff VK2MIA
VK2AVR
Forum Diehard
 
Posts: 444
Joined: Wed Jan 04, 2012 12:53 pm

Re: C-Pole antenna

Postby VK2FAK » Wed Jul 25, 2012 5:09 pm

Hi all...


Thanks Geoff, I have never seen that H-antenna before, but one of my main issues is the height and the H needs at least 10m from a quick look I had....I am mainly looking for something for the higher Freq. 17m- 10m.
I know the ideal at those Freq. is a beam but I don't want to go there....I may eventually make a second loop to cover those bands but right now just experiment a little.

The H-antenna goes into the folder for a closer look in the future......I love things that have never been used or bothered with over the years...

John
VK2FAK
Forum Diehard
 
Posts: 972
Joined: Thu Apr 15, 2010 6:28 pm

Re: C-Pole antenna

Postby ZL1RS » Thu Jul 26, 2012 9:05 am

will have to get around to buying EZNEC one of these days (the website has an eznec model file for C pole and H pole)


The .ez files on the H-Pole and C-Pole web pages display OK in the free 4nec2: http://home.ict.nl/~arivoors/

4nec2 automatically converts a .ez file to .nec before "working on it" and the plots for the C-Pole and H-Pole antennas at 20m come out the same in 4nec2 as the ones shown on their respective web page articles. One can then fiddle with the structure in the nec editor and/or produce plots over the frequency range you want.

"Running" the various .ez files on the C-Pole and H-Pole web pages in 4nec2 produced the following broad impressions:

The C-Pole antenna is a "half height", bottom fed, 20m vertical antenna with a good match to 50 ohms and radiation pattern on that band similar to a half-wave vertical dipole (with about 2-3dB less "gain" as would be expected from being short). The radiation pattern on bands from 17m to 12m is also OK ... but the feed point impedance on those bands might be difficult to match with a tuner.

The H-Pole antenna is more or less twice the height of the C-Pole and requires a tuner, but it appears to have a useful radiation pattern from 7-30MHz (except around 11-12MHz where the radiation angle is high). The antenna pattern and "gain" is still OK below 7MHz but the feed impedance becomes impractical (just a few ohms at 80m), otherwise the feed impedances in the ham bands from 40m to 10m seem reasonable for an auto tuner (there are however wild extremes in R and X between 11-13MHz and 26-27MHz).

73, Bob ZL1RS
User avatar
ZL1RS
Forum Diehard
 
Posts: 502
Joined: Fri Feb 08, 2008 10:29 pm
Location: Bay of Islands

Re: C-Pole antenna

Postby VK2FAK » Thu Jul 26, 2012 9:55 am

Hi all...

Bob...your probably right in what you say....I always look at gain figures with questions....

The most common one is how many people have the HF antenna's at the correct height to obtain those documented gain figures....it would be easier on bands above 20m to do this, but still difficult in a suburban block.....
Then comes how efficient is the standard HF antenna on those blocks...for a vertical, unless you have all those radials installed, it is going to have a low percentage of efficiency......The C-Pole is reported to have high efficiency and is still a manageable antenna.

Still looking at the design, mainly the balun at this point......but it all remains to be seen ...we will see.

John
VK2FAK
Forum Diehard
 
Posts: 972
Joined: Thu Apr 15, 2010 6:28 pm

Re: C-Pole antenna

Postby VK2YOJ » Thu Jul 26, 2012 11:25 am

Hi John
Have made & used a 20mtr Cpole antenna on lighthouse weekend for the last 3 years at a height of 3 mtrs to the balun on the back of the 4wd
Have found it easy to make & tune with good results on air, working into US & various island.
The balun is a home made coax type on poly pipe rg58.
Good luck.

Glen
VK2YOJ
Forum Novice
 
Posts: 2
Joined: Wed Jul 25, 2012 5:04 pm

Re: C-Pole antenna

Postby VK2FAK » Thu Jul 26, 2012 11:34 am

Hi all...

Thanks Glen.....it does look a good antenna for a portable situation...

Good to hear that you have had success with it, did you make the standard balun with about 60 turn of RG-58 or did you make it different...?

John
VK2FAK
Forum Diehard
 
Posts: 972
Joined: Thu Apr 15, 2010 6:28 pm

Re: C-Pole antenna

Postby VK2YOJ » Thu Jul 26, 2012 11:58 am

Hi John
From memory I made the balun included with the internet artical.
I made it from poly pipe with a pl259 socket mounted on the bottom of the poly pipe.
I have photo's I can send them to you. google tareetronics & Look at the bottom you will see my email.
Send me an email so I can get your address & I will send you a couple of pics.

Glen
VK2YOJ
Forum Novice
 
Posts: 2
Joined: Wed Jul 25, 2012 5:04 pm

Re: C-Pole antenna

Postby ZL1RS » Thu Jul 26, 2012 5:51 pm

For Geoff VK2MIA who wrote:
I would be interested to see if a more compact H-pole could be built that works using a 7m squid pole on 40m-10m.


The following observations were made after editing the "bottom fed" H-Pole antenna's dimensions (except the wire size) in the nec editor of 4nec2 to model a half sized version at the same height above ground (height of top wires = 5.8m):

The high angle radiation lobe frequency moves to between 22.5 and 24.5MHz (11-12MHz in the original)
The "wild" impedances are between 15-16.5MHz and between 25.5-28MHz (12-13.5 and 26-27.5 in the original)
Changing the open wire line length moves the higher frequency "wild excursion" more that the lower frequency one
The feed point impedance is VERY low at the 40m band ... R=1.45 and X=-586 (R=215 X=782 in the original)
The feed point impedance at the 15m band is also fairly low ... R=10 and X=130 (R=52 X=-8 in the original)

Disclaimer: the section of balanced line may not be correctly represented in the modeling (the Geometry view in 4nec2 does not appear to have exactly the same balanced line to feed point layout as the web site diagram) so YMMV.

As John VK2FAK points out, practical results will depend on local conditions.

The little SGC tuner shown on the H-Pole antenna web link looks interesting and is at an exceptionally affordable price compared to other auto-tuners ... but surely a coax line choke would be required in the coax line to the station? (Balanced feed line to an unbalanced tuner).

73, Bob ZL1RS
User avatar
ZL1RS
Forum Diehard
 
Posts: 502
Joined: Fri Feb 08, 2008 10:29 pm
Location: Bay of Islands

Re: C-Pole antenna

Postby VK2AVR » Fri Jul 27, 2012 9:18 am

ZL1RS wrote:The feed point impedance is VERY low at the 40m band ... R=1.45 and X=-586 (R=215 X=782 in the original)


Thanks Bob, suspected it would be the case! Dang.. :) Also the fact that feedline length matters indicates it is part of the antenna, which is not a good thing unless you're portable and don't care about feedline radiation. Sounds like it would be better fed with a tuner at the base of the antenna and a properly choked coax lead back to the Tx.

Geoff
VK2AVR
Forum Diehard
 
Posts: 444
Joined: Wed Jan 04, 2012 12:53 pm

Re: C-Pole antenna

Postby VK5PJ » Fri Jul 27, 2012 2:43 pm

Hi Bob,
ZL1RS wrote:For Geoff VK2MIA who wrote:
The following observations were made after editing the "bottom fed" H-Pole antenna's dimensions (except the wire size) in the nec editor of 4nec2 to model a half sized version at the same height above ground (height of top wires = 5.8m):
The high angle radiation lobe frequency moves to between 22.5 and 24.5MHz (11-12MHz in the original)
The "wild" impedances are between 15-16.5MHz and between 25.5-28MHz (12-13.5 and 26-27.5 in the original)
73, Bob ZL1RS


Are you able to do a quick edit of the model file to make a half size version that might cover up to 50MHz and see what the patterns look like then on 21MHz - 50MHz so it could be used as an antenna for 15 metres and up for on TX/RX and monitoring the gap between 30MHz and 50MHz?

Peter, vk5pj
User avatar
VK5PJ
Forum Diehard
 
Posts: 713
Joined: Sat Apr 02, 2005 7:38 pm
Location: Barossa Valley S.A

Re: C-Pole antenna

Postby ZL1RS » Fri Jul 27, 2012 3:22 pm

Also the fact that feedline length matters indicates it is part of the antenna

... but the feedline may not necessarily be radiating (however, possibly the case as the antenna is off-center fed). Remember that the H-Pole antenna is "non-resonant" which means it has a feed point impedance made up of a resistive component and a reactive component anyway ... and any length of open wire feedline will change that impedance at the far end. This may be a benefit if the auto-tuner can't handle the impedance on a particular band ... just add to (or cut) the length of open wire feedline until one finds a length that the auto-tuner will handle on all bands.

One could always go with a half sized version of the "original" H-Pole antenna and feed the center point of the "main" vertical wire, the whole antenna is balanced and fed with balanced feedline ... but (if the SGC is used) to an unbalanced auto-tuner :roll: The length of balanced feedline would be best run away from the feed point at right angles and this would not be an imposition as the height to the feed point on the half-sized H-Pole antenna is only 3m. One could fit a box on a post to house the auto-tuner ...

I'll have another play with 4nec2 this evening looking at that option
... and also check the predicted performance of the half sized version to 50MHz for Peter PJ.
... and try a the C-Pole antenna fed with a length of open wire line in the center of the vertical wire :wink:

73, Bob ZL1RS
User avatar
ZL1RS
Forum Diehard
 
Posts: 502
Joined: Fri Feb 08, 2008 10:29 pm
Location: Bay of Islands

Re: C-Pole antenna

Postby VK2FAK » Sun Jul 29, 2012 2:11 pm

Hi all...

Bob, when you mentioned the pattern for the C-Pole was Ok for 17m and above, did you punch in the numbers for the antenna dimensions..?

When I try, I have to adjust the the length of wires on the antenna to obtain a 1.24 swr reading with little loss compared to a half wave... but I am also using the simpler program mmana-gal..

Using the 4nec2, keep getting damn errors for something called Volumes on wires....no idea..

I will do on playing on 17m..

John
VK2FAK
Forum Diehard
 
Posts: 972
Joined: Thu Apr 15, 2010 6:28 pm

Re: C-Pole antenna

Postby ZL1RS » Wed Aug 01, 2012 3:45 pm

Ah, what a way to spend (waste?) an afternoon ... never mind, it was raining most of the time anyway :roll:

I ran more than 30 combinations of H-Pole and C-Pole antennas as well as just "simple vertical dipoles", all fed with various lengths and impedances of open wire line. All antennas are "non-resonant" therefore a practical version would have to be fed with a tuner. An automatic one like the little SGC SG-239 mentioned in the original H-Pole antenna article would make life easy in the HF bands at least, but being asymetric it should be followed by a "current balun" of some sort (see the original C-Pole antenna article).

Here is a summary of the more promising options from the 4nec2 software simulations. Note that sloping the open wire feedline from the feed point down to ground level skewed the radiation pattern on all antennas to some extent ... however, these antennas are short or shortened versions of the originals so the mounting height for an auto-tuner to achieve a perpendicular (horizontally run) feedline would be less than 3m except for antennas 5 and 6 ...

1) A "full sized" C-Pole antenna but fed with 3.75m of 550 ohm open wire feeder running horizontally from the center of the vertical section (5.1m overall height):
- Impedance would be tunable in the ham bands from 14 - 52 MHz with some "wild values" outside the ham bands (16-17 MHz and 32-34 MHz)
- the radiation pattern is a fairly constant low angle shape over that frequency range.

2) A "half sized" H-Pole antenna but fed with various length of 550 ohm ohm or higher open wire feeder running horizontally from the center of the vertical section (similar to the center fed H-Pole antenna article but only 5.8m in overall height):
- Impedance would be tunable in the ham bands from 14-52 MHz with some "wild values" outside the ham bands (and a fairly low R value in the 15m band)
- the radiation pattern is a fairly constant low angle shape over that frequency range.

3) A "half sized" H-Pole antenna fed at the bottom middle (as per the bottom fed H-Pole antenna article but 5.8m overall height):
- Impedance would be tunable in the ham bands from 18-52 MHz with some "wild values" outside the ham bands
- the radiation pattern has a high angle around 22-25 MHz but otherwise has a fairly constant low angle shape over the rest of the frequency range.

4) A "half sized" variation of the C-Pole antenna shaped like [ (e.g. without the open circuited 2nd vertical wire) and fed in the middle of the vertical section with various lengths of horizontal open wire line (5.1m overall height):
- some "wild values" of impedance at 2 frequencies between 18-52 Mhz. Changing the length of the feedline or the length of the top/bottom wires moved the "wild" frequencies as would be expected. Could probably tune on the ham bands from 14 to 52MHz
- the radiation pattern is a fairly constant low angle shape over that frequency range.

... but, for all the "fancy bent wires" of the C-Pole and H-Pole antennae, one may as well use a simple scaled down G5RV mounted vertically ... the radiation pattern is quite satisfactory and the impedance variations not too extreme. For example:

5) A 1/3 size G5RV mounted vertically, bottom end at 1m above ground (11.4m overall height):
- "wild values" of impedance at 16, 35 and 49 MHz but probably tunable on ham bands from 10-52 MHz
- the radiation pattern "breaks up and goes high" above 38 MHz.

6) A 1/4 size G5RV mounted vertically, bottom end at 1m above ground (8.76m overall height):
- "wild values" of impedance at 21 and 46 MHz, but probably tunable on ham bands from 14-52 MHz except 15m ("wild impedance" variation).
- the radiation pattern "breaks up and goes high" above 50 MHz.

7) A 1/6 size G5RV mounted vertically, bottom end at 1m above ground (6.18m overall height):
- "wild value" of impedance at 30-35 MHz but probably tunable on ham bands from 21-52 MHz.
- the radiation pattern appears more or less as one would expect from a vertical dipole over that whole range.

According to the software analysis, antenna 1) or 4) would probably work out the better overall options from 20m to 6m ... and maybe antenna 6) if lucky with the tuner matching at the 15m band.

Send me an e-mail if you want a specific .nec file or screen shot of "the curves" for that specific antenna.

Disclaimer: these comments are from observing computer simulations and "local conditions" may alter the results in practical antennas. These are vertical antennas with the majority of the radiation angle being low, so noise pick up may be a problem in urban areas (as with any vertical antenna).

73, Bob ZL1RS
User avatar
ZL1RS
Forum Diehard
 
Posts: 502
Joined: Fri Feb 08, 2008 10:29 pm
Location: Bay of Islands

Re: C-Pole antenna

Postby VK2AVR » Thu Aug 02, 2012 1:45 pm

Thanks for running those combinations Bob, very interesting!

Geoff
VK2AVR
Forum Diehard
 
Posts: 444
Joined: Wed Jan 04, 2012 12:53 pm

Re: C-Pole antenna

Postby N3DT » Fri May 23, 2014 2:42 am

I know this is a 2 yr old thread, but found it while re-visiting my C-pole information. I built an 80M version of KF2YN's C-Pole in 2007, but I used HB9MTN's dimensions. I pulled it up in a large oak tree and feed it with 100' of decent coax and I use a FT-240-61 core using 22 parallel turns of #14 enameled wire. I immediately found that it also resonates on 40M, and actually out performs a 40M version I also made. I've found I can tune it on nearly any band from 160 to 6M with my TS-2000, but I also have a 60M one hung up about 40' nearby switched at the base of the 80M one. I can switch between the two with a toggle switch at the op position, so I just use which ever one seems to hear best. Between the 2 I can work any band. I've recently re-hung one I made for 6M (actually cut for 25MHz) with 15 turns on the FT and am going to see how it works out this spring.

I've been quite happy with these antennas, they're pretty omni, nearly invisible in the trees which the OL likes. I filled up 2 pages of DX on 40M CW (EU) in 2 evenings.

I did correspond with KF2YN about the harmonic operation and he agreed that it would work. I'm not sure what the pattern is like though, I've never seen an .nec file of them. To me the C-Pole looks like an OCF dipole wrapped into a vertical C and that's why it works on the harmonic.

Just thought someone may be interested, I don't know why anyone puts up with radials if they can use the C-Pole. I've found very little interest in this antenna from the ham community.

Dave
N3DT
Forum Novice
 
Posts: 2
Joined: Sat Aug 31, 2013 2:17 am

Re: C-Pole antenna

Postby VK2FAK » Fri May 23, 2014 8:56 am

Hi All...

Dave..

When I was trying out some antennas I did build one, but what I am thinking is , that I may have confused a antenna that did not seem to work to good, with just a very quiet band, I tried it out on 17m and that band seems to be very quiet for me..so maybe the antenna was working as it should....

I did model the antenna and its patterns are very similar to a 1/4 wl vertical...with a good take-off angle(around 20 deg )..gain is just as similar to the 1/4w vert.

So you get the the pattern of a 1/4wl vert. without all the radial wires needed...and as you say can be used on other bands also...

I just had a look.... a version that works on 18.1MHz and has Vertical polarization and only about 0.05dBi gain when used on 36.2 MHz the Polarization goes Horizontal and a nice increase in gain to around 7.36dBi and still a good pattern BUT now directional with a take-off angle 20deg or lower.....of course you now have to match the antenna as the feed point resistance drops to around 13 ohms or less...

John
VK2FAK
Forum Diehard
 
Posts: 972
Joined: Thu Apr 15, 2010 6:28 pm

Re: C-Pole antenna

Postby N3DT » Fri May 23, 2014 9:53 am

All I can say is the 80M one I put up has measured swr 2:1 points at 3.5 and 3.7. Low is 1.17:1 from 3.57 to 3.61. On 40 M swr is 6.96-7.12 for 2:1 and min is 1.7:1 from 7.04 to 7.06. I haven't measured swr on any other bands as it's probably off the chart. I'm pretty sure I measured that right at the antenna with a service monitor and an rf bridge circuit.

The 25MHz one I tuned for 6M and is below 1.5:1 on the TS2000, but that's through about 50' of RG-6, so it's hard to say what it is for real, but the transmitter seems to like it. The 80M one will load on 6M with the TS2000 tuner and seems quieter than the 6M one, but the 6M one is lots closer to the house, almost right above it.

I did a plot with 4nec2 of a 20M one at 28.25 and it was showing a swr of 10:1. I kind of wonder if the ferrite I'm using isn't sucking up some power. I notice changing the turns on the toroid makes a difference where it resonates. I may try to optimize the 6M one in 4NEC and see if I can come up with something better.

I'll tell you though the 80M one works great for me and better on 40M, but I don't have anything else good to compare with. It's certainly much better than the 70' inverted L I have with a ground rod. It's surprisingly quiet for a vertical, but it's about 60' away from the house and we live in the boonies. There's no problem working into EU from here on the East coast on 80 and 40 with 100W as long as the bands aren't dead.

Dave
N3DT
Forum Novice
 
Posts: 2
Joined: Sat Aug 31, 2013 2:17 am


Return to LF, MF, HF



Who is online

Users browsing this forum: No registered users and 1 guest