As people have noticed from previous posts I have a very restricted area for antennas and a height limit of 10m.
My "Western HF10" dipole (G5RV jr with loading coils) is about all I can fit wire-wise and the current results are not good.
I have decided to use a rotating dipole for the higher bands but need a vertical for 30, 40, 80m (and 160m would be a real bonus).
So what are the options as I see them?
1. Turn the mast that is currently holding up the dipole into a non-resonate "mono-pole" over radials and maybe an auto-tuner at the base. I could add a horizontal wire to give extra length. Low cost option. Would also give me a vertical option on the higher bands. There are some commercially-produced ones, but how good is this type of antenna on the low bands?
2. A trapped vertical such as the Rippletech TZ-V-3L ( a bit over the height limit but who is going to notice) over radials. More expensive that option one but is the extra cost worthwhile for an antenna dedicated to these bands?
3. Comet CHA250 vertical. Would also give me a vertical option on the higher bands. Does not need radials. Expensive and the reviews are very mixed especially on its low band efficiency.
What say ye?
73
Wayne VK4WDM
Hi Wayne,
The G5RV was not meant to be an all band antenna and your experience shows that. That it's a Jr probably exacerbates the situation. At 10m you are limited for 80m and of course 160 for full sized antennas.
The WIA foundation manual describes a OCF dipole that will give reasonable performance on a number of bands. Don't forget height and radiation angle are related. Consider full sized wire loops and wire antennas supported by the ubiquitous squid pole. VK7JJ is a good place to start. A full length 40m 1/4 wave vertical is not unreasonable and a 30m vertical is definitely in scope. Drew Diamond describes a top loaded 160m vertical that is under 10m high. Ground radials for verticals are very important - investigate the option of buried versus elevated radials.
I don't understand how some commercial verticals claim good performance without a ground system. What science do they know that we don't? In my area we have one bloke who bought a Gap Titan antenna whilst the rest of us use wire antennas. He never hears anything on 40m while we can generally hear each other. That's a lot of money for no result.
I'd much rather spend a lot less money one or two antennas that work really well on single bands than hundreds of dollars on something that may perform the same or worse.
Antenna modelling is now within reach for all of us. Antennas can be easily evaluated right at your desk before before you start building.
A good antenna on 40m will keep you busy for a month of Sundays with digi modes even at this part of the solar cycle.
Now, if I remember correctly, you were the bloke that was addicted to wire antennas???
Addition:
I forgot to add that VK2OMD, VK5ZD and G8JNJ have written about the CHA-250. Looking at the specs of the TZ-V-4 I can't see why you'd spend that much money on something that you could probably replicate at home.
Wayne,
I can't knowledgeably comment on the first two suggestions but #3 certainly begs a response..
"3. Comet CHA250 vertical. Would also give me a vertical option on the higher bands. Does not need radials. Expensive and the reviews are very mixed especially on its low band efficiency. "
It is not only low band efficiency that is in doubt. The CHA250 uses a large "power swallow" resistor plus a balun effect so that the returned SWR looks ok to the transmitter if the basic feed impedance of the active vertical section varies widely from anything acceptable. The SWR might be ok but the overall efficiency is generally woeful on both transmit and receive. The "Does not need radials." gets me because basically ALL verticals need to operate against a ground plane to get any efficiency, the only exception that readily comes to mind being J-poles.
I think I would probably look at idea #1 more closely. While you don't give any details of the existing mast size, maybe if you can put an insulator under it and base feed it either direct or via selectable loading coils from your remote ATU (you still need ground radials) ? Alternatively maybe use a wire parallel to the mast itself and attach it part-way up, gamma match style, often used by low-banders who use towers with their HF yagis to act as capacitive top hats.. Maybe multiple wires attaching at different heights up the mast until you find the optimum one(s) for the bands you want to use ?
Unfortunately, apart from small rotatable loops with their very narrow bandwidth, antennas generally need to be large and at least 1/4 or 1/2 wavelength (or multiples) to have any efficiency and this, coupled with small yards, just doesn't work out well.
73 Doug
(03-11-2017, 07:40 AM)VK3ALB Wrote: [ -> ]Hi Wayne,
The G5RV was not meant to be an all band antenna and your experience shows that. That it's a Jr probably exacerbates the situation. At 10m you are limited for 80m and of course 160 for full sized antennas.
The WIA foundation manual describes a OCF dipole that will give reasonable performance on a number of bands. Don't forget height and radiation angle are related. Consider full sized wire loops and wire antennas supported by the ubiquitous squid pole. VK7JJ is a good place to start. A full length 40m 1/4 wave vertical is not unreasonable and a 30m vertical is definitely in scope. Drew Diamond describes a top loaded 160m vertical that is under 10m high. Ground radials for verticals are very important - investigate the option of buried versus elevated radials.
I don't understand how some commercial verticals claim good performance without a ground system. What science do they know that we don't? In my area we have one bloke who bought a Gap Titan antenna whilst the rest of us use wire antennas. He never hears anything on 40m while we can generally hear each other. That's a lot of money for no result.
I'd much rather spend a lot less money one or two antennas that work really well on single bands than hundreds of dollars on something that may perform the same or worse.
Antenna modelling is now within reach for all of us. Antennas can be easily evaluated right at your desk before before you start building.
A good antenna on 40m will keep you busy for a month of Sundays with digi modes even at this part of the solar cycle.
Now, if I remember correctly, you were the bloke that was addicted to wire antennas???
Addition:
I forgot to add that VK2OMD, VK5ZD and G8JNJ have written about the CHA-250. Looking at the specs of the TZ-V-4 I can't see why you'd spend that much money on something that you could probably replicate at home.
Hi Lou
"Now, if I remember correctly, you were the bloke that was addicted to wire antennas???"
Quite right, but a move to this QTH with a tiny back yard, plus a plea from the XYL "don't put wires everywhere this time" has cured the addiction!
I have used a squid pole vertical here but one of the sudden storms we are prone to wrecked in about 30 secs. I still have one for portable use.
Wayne
I only put the Diamond vertical in the mix because I knew that the idea of a "radial-less vertical" would arc some people up. We all know what will be acting as the second half of the antenna - the coax feeder, with all the problems of common-mode currents that goes with that scenario.
Lou, I disagree that the Rippletech trapped vertical is over-priced. The other station that I operate from, VK4KG, has the 40-10m model and it is very well made and works well, and I am sure that a lot of experimentation and testing went into its production that needs to be recovered in the price. Home brewing a trapped antenna would certainly be beyond me, and I expect it would be beyond a lot of hams. As you say there are a lot of wire antennas that would perform better but they are not possible or desirable at this QTH.
Doug, the existing mast is 10m high and is tilt-over. It would not be hard to put an insulator a the bottom and fed it against ground with an unun and putting out some ground radials would be easy. A wire from the top of the mast to the corner of the block would give me an "inverted L" about 14m long when is the same as the popular 42ft vertical marketed by DX Engineering. This is obviously my preferred option unless there is evidence that the trapped vertical would be better.
73
Wayne VK4WDM
Wayne
Re "
Doug, the existing mast is 10m high and is tilt-over. It would not be hard to put an insulator a the bottom and fed it against ground with an unun and putting out some ground radials would be easy. A wire from the top of the mast to the corner of the block would give me an "inverted L" about 14m long when is the same as the popular 42ft vertical marketed by DX Engineering. This is obviously my preferred option unless there is evidence that the trapped vertical would be better."
Extract from my web page at
http://www.vk4adc.com/web/hf-projects/45...na-options titled "
Portable HF Antenna Options", 29 July 2017:
"
A large resonant antenna (eg full size dipole) will always be more efficient than a reduced-size antenna (eg a trap dipole), which will always be better than an untuned whip (eg a squidpole with vertical wire radiator) and it, in turn, is more efficient than a helical whip (even though it too is resonant). Size is important!
I set about comparing three antenna types during a recent trip with the caravan out to a bush campsite, plenty of space and low noise levels. The reference antenna was the trap dipole, the frequency around 7110KHz on the 40 metre band, the signal source was a VK3. The coaxial feeders from the antennas were terminated in BNC plugs which made it possible to change through the three antennas all within a minute thus virtually eliminating QSB effects.
The outcome was: trap dipole = S9, 7 metre vertical squidpole with 4:1 UN-UN = S7 (& occasionally to S8), Mobile One M40 helical whip = S5. The relative signals test was repeated the following day at a different campsite, similar dipole direction, and that provided exactly the same results (S9, S7, S5).
I have noted previously there has been a one-to-two S-point difference between a full size dipole versus the trap dipole with the full-size dipole providing the stronger signals.
The summary effect is that if you have enough space available then erect full size dipoles, if not then try to fit the trapped versions, even just for short-term portable operations."
Note the signal level comparisons between full size & trapped dipoles and untuned (/ nonresonant) vertical antennas.
The same comparisons should be mostly true for a trapped vertical = trapped dipole provided that the vertical's ground effect in place will mimic the second side of the dipole at all frequencies. Similarly, mast radiator = squid pole, provided the a suitable ground effect in place for either instance.
Based on the above comments and where you are dealing with several bands, a larger array of independent wires is required to provide a suitable multi-frequency ground effect, not just a single 42ft wire.
The XYL may have said to reduce the wires that she could see but maybe didn't realise that some of them could go just under the ground's surface. Still there, just not visible.
73 Doug
(03-11-2017, 07:51 AM) Wrote: [ -> ]The CHA250 uses a large "power swallow" resistor plus a balun effect so that the returned SWR looks ok to the transmitter if the basic feed impedance of the active vertical section varies widely from anything acceptable."
There's no resistor in the CHA250, but it still doesn't work very well. It's easy enough to "roll your own" if you have a suitable vertical element.
If you want to spend some money then I'd go with a vertical sitting on an auto-tuner (e.g. EDX-2) with whatever ground radials you can manage.
73
Iain
Iain
"There's no resistor in the CHA250, but it still doesn't work very well."
Maybe my memory is playing tricks on me but I sold Comet products back 10+ years ago and I was pretty sure there was. Maybe they have changed the recent design but not the model code. If it wasn't the CHA250, then at least one other manufacturer back then was doing as described (swamping resistor/balun..) and selling a 3-30MHz vertical 10 metres long, no radials required, SWR guaranteed not to exceed something like 3:1 across the full range. They also sold a longwire version with the same feed unit, just the wire was longer than the vertical model.
Must be signs of old age creeping in
73 Doug
I took my CHA250 apart some years ago.
A couple of brass tubes, some ferrites and a bit of wire.
Not hard (and cheaper) to build your own.
[
attachment=96] [
attachment=97]
Internals
[
attachment=98]
Circuit
Well, just to show my ignorance of antenna theory, I ask:
In the circuit diagram it shows that both 'sides' of the feed from the transmitter attach to the right-hand tube, which appears to be metal in the photo.
Why does this not simply present a short-circuit to the transmitter?
(05-11-2017, 08:42 AM)VK2CSW Wrote: [ -> ]Well, just to show my ignorance of antenna theory, I ask:
In the circuit diagram it shows that both 'sides' of the feed from the transmitter attach to the right-hand tube, which appears to be metal in the photo.
Why does this not simply present a short-circuit to the transmitter?
The thing that the wiring diagram does not show is the fact that the two metal tubes are inside ferrite rings/sleeves which will make the impedance from one end to the other a relatively high impedance, even at HF. What is not disclosed by the photos is the grade of ferrite involved so it becomes difficult to figure out the actual values of the design. Look at the detail within the red rectangle as it reveals most.
The twin tubes within the two rows of ferrites is a well known technique and described in many articles on the web, and even one that appeared in AR magazine within the last few years. Solid state PA output stages have been using it for many years (>20) particularly for push-pull outputs where the transistor output impedance is so low and is essentially the multiple turns through the sleeves are just a wide-band impedance step up transformer. The one in the Iain's diagram looks to be basically a 1:3 turns ratio so about 1:9 impedance transformer, ie 50 : 450 ohms. The top of the transformer connects to the vertical radiator hoping that at any applied frequency, the feed impedance will be somewhere approximating 400-500 ohms - which will only occur at a relatively few frequencies within the HF range.
The overall antenna design still requires a ground plane to be used if it is going to be an effective antenna.
73 Doug
See also :
http://www.g8jnj.net/cometcha250b.htm
http://www.vk5zd.com/CHA250/CHA250.aspx
Thanks for the explanation, Doug.
I get it, although a lifetime of playing in the DC world makes it appear illogical - I need to free my mind of those shackles
Wayne
After my last caravan trip, I set about building up a multiple ratio UN-UN to use with my 7M long wire squid pole style antenna. I used a FT140-61 toroid with quadrifilar windings and where the joints between the windings are, those points were taken to separate connection point screws on the ABS box housing. That gave me ratio points of 4:1, 9:1 and 16:1 that I could attach the antenna wire end to via a crocodile clip. The earthy side of the assembly connected to the coax connector and thence to the caravan frame via a second croc clip and braid.
I tried measuring the impedances on the various bands using my homebrew Z-analyser and squid pole wire and determined which ratio tap would work best on any particular band by looking for a resistive component between 10 and 100 ohms coupled with as close to a zero reactive component. That gave me starting points for all bands 80 metres to 10 metres, WARC bands included. I couldn't get anywhere near a satisfactory outcome on 160 metres, and 80 metres was questionable.
Next I used my IC706Mk2G via an LDG Z100 autotuner into the UN-UN and repeated the tests band by band. The setting as to whether the tap was 4, 9 or 16:1 was less critical as the autotuner adjusted for each band but I couldn't achieve a match on 160 metres regardless. The autotuner did match on 80 metres though I have doubts as to how efficient the antenna would actually be there.
I haven't done exhaustive tests to see how effective the UN-UN and 7 metres of wire(/squid pole) are as an antenna assembly but will probably see how it goes on my next bush outing, somewhere where it is quiet and isolated. I have added a trapped-wire arrangement to the portable kit so it is an alternative to the squid pole/UN-UN and it covers 80, 40, 20, 15 and 10 metres (using 4 homebrew traps on PVC pipe). It is (again) run against the metal caravan frame but only needs to be elevated at one end, and clips to the centre pin of a coax panel socket connector, the outer frame again via a braid and croc clip to ground (no BAL-UN or UN -UN). In essence it is just half of a trapped dipole but is light and easy to erect and operates on the 5 most likely bands. Most of the details are similar to the design described at
http://www.vk4adc.com/web/index.php/hf-p...v-v-for-hf. If I recall correctly, the total length was about 10 metres (for the one side) so that is close to your target of 10 metres, do-able if you slope it a bit such that it is close to the mast at the top and spaced out at the base. You can also add traps to make it operate on 10, 18 and 24 MHz if you want to. Worth a thought.
73 Doug
PS My 19 metre length of wire tunes well on 80 metres, but then again it is about 1/4 wavelength..
Really interesting Doug. I am sure others have enjoyed it too. Has it been published in AR?
I have had to give up the idea of mounting a rotatable dipole on my VHF/UHF mast because there is not enough room for it when the mast is lowered, so the vertical will have to be 80-10m.
I will try turning the present HF mast into a non-resonate monopole/inverted L because I already have an auto-tuner and it would be an easy task. If that does not work out will have to go to a commercial antenna.
Although I love puddling around with bits wire and metal, the reality is that the arthritis in my hands is making it more and more difficult for me to make, build and repairs things so buying is becoming the only option.
I have been offered a new Diamond CP6 at a very good price. I know the reviews are very mixed but some get very good results with them. Any opinions out there?
I am going on a cruise tomorrow and my postings may be irregular for a few weeks.
73
Wayne VK4WDM
Wayne
Nothing published about it in AR but it would be published on my web site at
http://www.vk4adc.com if it was anywhere. There are a lot of things/projects that don't even end up there because it is very time consuming creating the articles.
The Diamond CP6 has very narrow bandwidth as you go down towards 80 metres so unless you specifically tune and operate within its low SWR window, your overall results will likely be poor. Eg...
80m : +/- 9KHz at 1.5:1 SWR points (so you have to tune it centred for the very narrow segment you wish to operate in),
40m : +/- 14KHz at 1.5:1 (ditto),
20m : +/- 50KHz at 1.5:1,
(and a lot better from here up).
An in-line autotuner option does not make up for the non-performance of the antenna outside the denoted 1.5:1 bandwidth points, it simply provides a better match for the radio's output impedance.
Have a good time cruisin...
73 Doug
For info about the CHA250B...
I was perusing my HDD archive today and found a Comet folder and it contained a CHA250BX file dated 2009.. The part that was of greatest interest was the frequency coverage graph as attached below.
The lowest useful frequency dip is about 4MHz rather than 3.6, but does show SWR dips around 7 and 10MHz, more-or-less skips 14, then low 20's & low 30's, another dip mid to high 50's. The scaling shows < 2:1 across the spectrum from about 3MHz to 90MHz.
Given that it is basically a vertical radiator < 7M high/long plus the previous comments on the impedance matching UN-UN at the base, it seems hard to figure out how the low SWR is achieved across the bandwidth - unless the UN-UN ferrites are so lossy that they 'swallow up' the RF. Low SWR but poor efficiency if that is the case, both on transmit and receive.
Verticals still require ground planes - even ones like this..
73 Doug
Hey Wayne,
do you know anyone with one of the old / scrapped CODAN lunchbox radios (6924 I or II) the load control in there is a tapped / stepped rf transformer that is ideal for matching verticals. Of course be aware it is designed for LOW power but using it as a ready made test device is a good start. (then build a bigger QRO version)
I used one of these out of a 6924 at the bottom on my mobile HF whips and even on Rx the right choice of the tap point showed improvements in receiver noise .. hint, position 5 is about 1:1 impedance.
Peter, vk5pj
(03-11-2017, 06:49 AM)VK4WDM Wrote: [ -> ]As people have noticed from previous posts I have a very restricted area for antennas and a height limit of 10m.
My "Western HF10" dipole (G5RV jr with loading coils) is about all I can fit wire-wise and the current results are not good.
I have decided to use a rotating dipole for the higher bands but need a vertical for 30, 40, 80m (and 160m would be a real bonus).
So what are the options as I see them?
1. Turn the mast that is currently holding up the dipole into a non-resonate "mono-pole" over radials and maybe an auto-tuner at the base. I could add a horizontal wire to give extra length. Low cost option. Would also give me a vertical option on the higher bands. There are some commercially-produced ones, but how good is this type of antenna on the low bands?
2. A trapped vertical such as the Rippletech TZ-V-3L ( a bit over the height limit but who is going to notice) over radials. More expensive that option one but is the extra cost worthwhile for an antenna dedicated to these bands?
3. Comet CHA250 vertical. Would also give me a vertical option on the higher bands. Does not need radials. Expensive and the reviews are very mixed especially on its low band efficiency.
What say ye?
73
Wayne VK4WDM
Update on this. I ended up making an ally tube vertical 10M tall. The lower sections are double wall so it is self supporting but I will consider adding guys if wind sway gets too scary. I then added 12M of wire to the top that slopes down to a 5M mast on the corner of the block so I now have a sloping "inverted L." The wire length is solely based on the distance available. I have an earth stake but no radials as yet but plan to add some in the next few days.
It is obviously a non-resonate length but the internal antenna tuner (more correctly a transmission line matcher) allows me to use it on all bands 80-6m, and with an external tuner, on 160M. Early results seem quite good on 80 to 20M. Not much activity on the higher bands to check. Also worked all over VK-ZL on 6M when Es were active. Like all verticals it is a bit noisy on the low bands but the Yaesu FTDx-1200 has very good noise mitigation.
The next move is to try it with an auto-tuner at the base.
73
Wayne VK4WDM
That's good news Wayne, another success story.
If you need to guy it, use strong fishing line...it is almost invisible.
Paint it matt green and if possible make it "grow" after about six months when everyone is used to it. Hi Hi.
An auto tuner at the base and some radials would be ideal...eliminating excessive coax losses.
Cheers
Nev
Wayne
"I ended up making an ally tube vertical 10M tall. The lower sections are double wall so it is self supporting but I will consider adding guys if wind sway gets too scary. I then added 12M of wire to the top that slopes down to a 5M mast on the corner of the block so I now have a sloping "inverted L." The wire length is solely based on the distance available. I have an earth stake but no radials as yet but plan to add some in the next few days.
It is obviously a non-resonate length but the internal antenna tuner (more correctly a transmission line matcher) allows me to use it on all bands 80-6m, and with an external tuner, on 160M. "
Are you feeding the coax inner conductor to the base of the tube directly or via an UN-UN ??
If UN-UN then ratio ??
Doug