Ground plane input asked

As you might know i've  build an HF antenna from a silver rod(actually 2 rods).  Now i'm experimenting again with the ATAS-120. I want to mount this one on a aluminum pole of 6m. Everything i read about using an ATAS as a base station antenna mentions ground plane, counterpoise and whatever it is called. I'd like to use the mount of a silver rod and also found these, from one of the silver rods

Would they be useable for a ground plane/counterpoise for the ATAS or could i use their mounting points for some lengths of aluminum tubing (about 1.5m max). Is, similar to what is said about antenna's, the old saying: "A bad counterpoise is still better than no counterpoise" still true?

I'd like your opinion.
73
Karel

It very much depends on what band(s) you wish to use the antenna on? General rule of thumb is the lower down in the band you go, the longer counterpoise is needed.

Yes, but what did these small "radials" do on originally an 11m antenna? Think they would be way too short.

To be honest, on 10 and 11m it's not really necessary to have them. I usually only run a suitable counterpoise from 40m to 20m, nothing on 10/11m.

A bit complex but I will try and explain in a short way. As I understand ATAS-120 is a tuner so I assume you are mounting this on the base / feed point ? We can only assume for now.

A counterpoise can be seen as 2 things, a place for "return currents to flow" instead of your coax which may start to radiate and mess up your radiation pattern.

It is an attempt to make a not very good antenna a bit better in my opinion. (more like a weird type of non mirror image dipole.)

A ground plane is what certain antenna lengths need in order to work properly. i.e. 1/4 wave and 5/8 wave. A 1/4 wave is current fed so it needs radials to form the other half of the antenna.

I generally look at a 1/4 wave as a 1/2 wave dipole with 3-4 legs at 45 degrees.

The ground plane (radials) is half of the antenna system in this case and is required in order help match the antenna and make it more effective. A 5/8 is a mix of current/volts at feed point so it has a capacitive reactive load at feed point if I recall correctly so it needs radials and they also help match to 50 Ohms.

As this will be a multiband antenna your antenna will be a fixed length relative to a changing wavelength as you are shifting frequency. As such your antenna will  become more or less like a 1/2 wave, a 1/4 wave and a 5/8 wave at different frequencies.

I would put 4 x 4 meter wire radials at 45 degrees as some kind of sensible starting point if you plan working that antenna with 10m through 20m. If that is possible.

That will help tuning / efficiency a bit and act as counterpoise for what will be a compromise antenna on some bands.

It is likely the small radials for a 1/2 wave CB antenna did nothing at all. Not even worth being there. A tiny counterpoise for an antenna that arguably does not need it as it is voltage fed so there is very little current at the feed point that needs to dissipate. (Theory dictates a 0.05 wavelength counterpoise is good for belt and braces but many use nothing in ham world for 1/2 wave end feds)

Tried the small original "radials" and you're right, they don't aid in tuning whatsoever. My ATAS tunes on 40m and 10m automatically to 1:1.1, on 20m i have to wait for a dip when autotuning happens, stop autotuning and fine tune it with the up and down function keys on the FT-897( can get to just about 1.5). Strange, most complaints about the ATAS are concerning the 40m band.
The next experiment will be with 3 aluminum radials of about 1m each(diameter 10mm,have them still laying around from a previous build dipole for 11m) at a downwards angle of about 30 degrees (read that somewhere). If thats not satisfactory i'll add some 8mm lengths (also from the same old dipole). The next steps will be using angles of about 45 degrees. Suppose one of those solutions will do the trick, I don't have the space for radials longer then 2m each.

73
Karel

I would save time and put your 2m radials on first time as they at 2m are probably still too short.

You radials will be a compromise at all frequencies. Consider that a 5/8 waves's radials are ideally 4 x 3meters long (9 feet) and that is just for 10 and 11meter band. For 20m they need to be 5m+ meters long ideally if using only 4.

Or you can start making them shorter and add 16 or more. That's just how this stuff works. On 10/11m even a 1/4 wave radials are 2.5m long.

The counterpoise / radials thing is complex and my recall is a bit hazy at the moment.

There is something called Kirchoff's Law. which suggests something along the lines that equal currents must flow out of a circuit (if not dissipated by components as heat) on another conductor and I think this is the idea behind a counterpoise. Don't quote me though as I might have that a bit wrong.

Counterpoise is usually used with a compromise/quick set up/not very good/portable antenna as a "quick fix". It can maybe help tuning/SWR. It might very slightly help you with a little less ground losses, often just laid on the ground froma vertical... i.e. efficiency. (ideally you don't want too much of your expensively generated RF heating worms in the ground) Though a single counterpoise will not give much help you need a radial field on the ground.

Counterpoise can be helpful on multi-band antennas as you are asking what is random wire lengths essentially to be a compromise of a 1/4 1/2 or 5/8 ideal antenna.

Counterpoise can also be the mounting pole especially in the cases of a vertical which often has a metal bracket that connects to metal poles. Unless you isolate the antenna fro the pole. The effects of this are rather difficult to predict. Is the pole earthed ? How long is the pole ? Are their common mode currents on the pole etc. can influence how the pole can affect the antenna system.

All bits of wire radiate even 0.5m of wire will radiate a signal that might be picked up on the other side of the Atlantic. And in very high ionization you will make some contacts for sure, maybe some impressive ones, but all bits of wire are not good antennas. They are sub optimal antennas falling short a bit. (or a lot on some bands if unlucky, as in lose DX levels of bad)

Radio often has to be what can fit your situation and you just work with it.

Then it is a operational hours to get the right luck to appear and a waiting game.

You may want to consider adding a ferrite based coaxial choke 1:1 isolator in line at feed point to keep and CMC off your coax. These are broad banded (unlike the ugly balun) It will allow your radiation patterns to be as good as the piece of wire length relative to frequency of operation can be.

Good luck.

Quote :

You may want to consider adding a ferrite based coaxial choke 1:1 isolator in line at feed point to keep and CMC off your coax. These are broad banded (unlike the ugly balun) It will allow your radiation patterns to be as good as the piece of wire length relative to frequency of operation can be.

Good luck.

Would that not interfere with the DC power for the ATAS?

Your question was about counterpoise/radials. I do not know the specifics of your ATU or how you intend to use it (at the feed point of the antenna would be best as I understand).

I also thought your ATU is design for a very specific Yaesu produced antenna/whip ?

I assume DC power to ATU is received via antenna connections and coax. If so DC will not be affected by coils in coax (it will just produce minimal DC resistance) 

AC is affected by coils, they create inductance. And are why coils are used in loading an antenna.

The choke I am thinking of is the big ferrite with something like 7 turns on it, it is shown in our Amateur radio manuals RSGB.

Something like this, they should be fine down to 40m band.

https://moonrakeronline.com/blog/how-to-make-an-rf-choke

Some ideas i'm thinking of:
- Could CB whips be used as a counterpoise?
- I have 2 more or less complete silver rods. Could i use one of them as one sloping radial (think i just have enough room for one)
- You can shorten the needed length of an antenna by using a coil, does the same apply to radials?

I always used CocoaNEC on my Macbook, Now i've installed Linux with Wine and 4NEC2 on a desktop. Think this will be a nice learning experience for learning 4NEC2. I read too much info on the internet, some contradicting each other. Laying radials on the ground vs. don't let radials touch the metal mast or connect them to ground ????????

Firstly consider your and others safety. That is No.1

You have not given much info about where this antenna is mounted or how so impossible to reply with much accuracy.

Use some common sense when working your installation out and don't rig up anything unsafe.

Wires.. easier to hang and drape, stretch out and lighter. Aluminium, good for horizontal (hold themselves up) use reasoning to work out your solutions.

Radials = depends on your connections/install, you can choose.

Most people build on the ground and do basic tests first.

Your installation is 100pct unique. That specific location does not exist anywhere else in the universe so you must test "in-situ".

Many antennas do have radials that are connected to the mast (usually via a bracket), many ground mounted antennas lay them on the ground. Personally I have not used an antenna where the radials are knowingly and intentionally connected to the ground (soil) itself.

That is to do with earthing and that I am making no commentary about. You must find out about that yourself.

You can load radials as far as I understand. How bad are you planning to make this antenna perform ?   

You are making something from old parts you have in your shack, and there is nothing wrong with that but what is written on the internet may or may not apply to what you are doing. As such you must experiment and find out.

Few have done what you are doing. Instead they use a fibre glass pole and run a wire up it with an ATU at the feed point with plenty of radials. i.e. a ground mounted multi band HF antenna.

Experiment an find out what is working and what is not.

Is this to be ground mounted or elevated ? If elevated make sure you don't have poorly secured radials made from aluminium attached. That's just dangerous.

Good luck, over and out.

FreqFreak wrote:

I would save time and put your 2m radials on first time as they at 2m are probably still too short.

Finally found some specs on the original ATAS-GG hf radial kit on a german site. You're probably right, they use 8 2m radials. For 40m they advise an extra wire, somehow connected and wound through the radials, but i have to translate that from German, so not sure what they mean. Google translate isn't that good  .
As for the size mentioned i can somehow understand it, the ATAS is a mobile screwdriver antenna and should also work on the normal size cars.

Perhaps some clarification of my setup is in order. I'm using a Yaesu FT897 combined with an Yaesu ATAS-120a screwdriver antenna. The antenna is mounted on a 6m aluminum pole, which in turn is mounted to the side of my garage, about 50cm above ground. My garage has a flat, non conducting roof at about 3m high, so the mounting point of the antenna is about 3.5m above the garage roof.

I am not an SWR addict (might be sending through dummy loads if i was ) but apparently my FT-897 is. If the antenna is not tuned i get a HSWR message and the FT-897 just refuses to send.

In the past i have mounted the ATAS on a piece of metal(about 1m by 0.75m) laying flat on the garage roof. Then i had trouble autotuning on 40m as can be expected, but 20 and 10m tuned fine. All and all this led me to think i need some counterpoise now that i've raised the antenna to 6.5m.

Have you thought about the base kit they sell for that antenna.

You have to do what you have to do but I suspect this antenna will under perform without a large skin of metal directly under it.

It is a bit confusing as to why you are mentioning what is designed as a mobile antenna and old silver rod parts. I can only imagine you are trying to make the silver rod element your radiating element attached to the ATU part of this system ? I am just not sure it is going to work, I think the cheap UK Silver rods are DC shorted to the bracket and am not sure how that would affect things either (though that likely happens through the coil which I can only imagine you have removed as it will hinder matching).

The reason why short whips tend to perform above what might be expected is due to the unusually large metallic ground plane of a vehicle underneath. Which is a lot of metal surface area for the antenna to work off. I suspect that not having that very large ground plane under it (like an extensive radial field) is going to make the antenna a bit underwhelming.

Not to be forgotten people generally go somewhere in the countryside with a nice low noise floor and clear view to the horizon both aspects of which counts for a lot.

It is not even as long as a ham stick at 1.4/1.6m Hamsticks are about 2.4 meters.

I would hate to see you waste your time.

I believe you would be better off buying a 12m fibre glass pole putting something like 7m of wire (or whatever is recommended for a multiband HF antenna) on it and tuning that with as much radials as you can manage. 4 copper wire radials coming down and tied off somewhere would help.

I am concerned you are going to make an unsafe structure that will not work very well anyway.

I presume you have checked your noise floor locally ? Be a shame to see S7 of noise on a vertical.

I just like to DIY. So far i came up with this:



Which now also doesn't tune on 40m anymore. Think i can extend 2 of the radials to 2m. If that doesn't work i can always bend them down to 45 degrees. After that it's back to the iron plate on the flat roof of the garage, maybe with some extra radial wires laying around.

Well, it's back to the iron plate on the flat roof of the garage . Then it will tune, but in my urban environment it is not enough height to get some range from it. Alternatively i could extend the radials to a lot more, but id don't think my neighbours will like having my radials hanging above their gardens. Raising a car on top of my garage also is not an acceptable option . Thanks for all your input, i've learned a lot of this experiment. Anyone like to buy an ATAS-120a? I'm going back to my CB Silver rod HF multiband setup.

73,
Karel