Ground plane basics

[321 treeclimber]

What do the radials actually do ? Maco 5/8 40'ft. To the tip from a 20'ft. High flat roof. How does it work? Ive gotten the swr down to 1.2 on chnnl 20,11m by setting the overall lenghth.hears great, talks great. Just curious as to the radials.my other antennas were straight sticks. Antron99,bigstick,sirio27 and others. Any easy way to understand ground plane radials?

[ytradio]

It is the other half of the antenna, as in a dipole, which basically, all antennas are. Even though some antennas do not have radials, something else is making up the other half, usually the shield of the coax. Sometimes this works out pretty well, and sometimes not, depending on coax length and many other factors. The radials provide resonant lengths for this second half, and this helps to isolate the coax from working as part of the antenna. A vertical will work with only one radial, this antenna is called an L. By putting 2 or more radials evenly spaced around the vertical, it makes the patern more uniform. A mobile on the other hand is using the car body for the second half of the antenna. Just not all that practical to put resonant radials on a mobile.

[Sandbagger]

Dec 28, 2018 12:06:49 GMT -5 321 treeclimber said:

What do the radials actually do ? Maco 5/8 40'ft. To the tip from a 20'ft. High flat roof. How does it work? Ive gotten the swr down to 1.2 on chnnl 20,11m by setting the overall lenghth.hears great, talks great. Just curious as to the radials.my other antennas were straight sticks. Antron99, bigstick, sirio27 and others. Any easy way to understand ground plane radials?

A vertical antenna is composed of 2 parts - the "hot" side or active element, and the ground or counterpoise side. If you mount the antenna at ground level, the earth becomes the counterpoise. In order to raise the antenna above ground level, you need to construct an artificial "ground", and that's where radials come into play. They play the part of the ground, to give a lower angle of radiation, and to properly decouple RF currents.

This is my major beef with radial-less "stick" antennas like the A99 and the Imax. They are designed to work without radials. And while they can achieve a good SWR, lacking radials means that there is not an effective counterpoise. RF currents are not properly decoupled, and they tend to flow along the outer shield of a coax all the way into the shack where they can cause all sorts of havoc with RF feedback, and near field TVI/RFI interference. There is a persistent claim around the band (and forums) that the A99 is a "bleed stick". It's a reputation earned due to the lack of proper decoupling. Many RFI issues can be solved or greatly reduced by replacing one of those "stick" antennas with a proper ground plane (with radials).

[321 treeclimber]

Got it. And thats what i thought.to put the antenna up over local obstacles like our catskill mountain tops,you have to then bring the ground plane up to it,to get the same reflection...not sure if thats the right term but i get it. I have another little cabin with a steep 12on12 roof pitch but it sits at 1500feet on the top of a hillside and its got a metal roof. If i mount my antenna on the peak,dead center and on ten feet of mast,will that roof help or hinder ?

[ytradio]

Hard to say what the performance may be at 10 ft above your metal roof, one way to know is try. An interesting situation you have is the 12 on 12 pitch. That’s a 45 deg. Down sloping angle, same as 1/4 wave vertical radials. I personally would be very tempted to try putting a 102 inch whip right at the peek instead of 10 ft up on a pipe. The roof pitch is probably to long to make a perfect radial length, but like daddy always said, nothing beats a try but a failure. The large metallic ground plane should work pretty well at any rate. Also being at the elevation it is, I would like the radiation angle on a 1/4 wave better, flatter lower angle. Bigger and longer is not always better, I know, that’s NOT what she said. 73 Whitey

[321 treeclimber]

Hahaha! Thanks whitey, im gonna give it a try. I have a steel whip to try but ultimately I'll need something that will handle some power. Im also restoring an old moonraker4 and a used 40'ft tower. Thought being too close to that metal roof may not be a good idea in that case.

[ytradio]

The whip will Handle quit a bit of power, and being a quarter wave it should match very well. Also don’t be afraid to try something that may be what some guys on the radio will tell you will never work. I have seen antennas work that have left everyone scratching their head. But the proof was in the pudding. If the exact same antenna were copied in another location, maybe would not work worth a crap. There are just too many variables. But there are many proven and predictable antennas out there that you can always fall back on. Try looking at hamuniverse antenna design page, it’s a great place to see many antennas with some good explanation. 73 Whitey

[321 treeclimber]

Roger that . I am at that point in time where im havin so much fun and learning so much about the tech end of this hobby that im gittin ahead of myself. First things first,hahaha if i keep jaw'n bout antennas I'll have half'a dozen in the works and nothin on the roof

[ytradio]

Understood, antennas are a great place to experiment, and building them is satisfying and fun. Like Dudley Moore in Arthur said “ isn’t fun the best thing to have”.

[321 treeclimber]

Well, its been awhile since anyone has quoted such an important film as arthur! This must be serious. Hahaha! Ok I'll keep experimenting and in the immortal words of bugs bunny,"Hoboken! Ooo I'm dyin"! Thanks whitey

[SIX-SHOOTER]

Dec 28, 2018 15:34:08 GMT -5 ytradio said:

It is the other half of the antenna, as in a dipole, which basically, all antennas are. Even though some antennas do not have radials, something else is making up the other half, usually the shield of the coax. Sometimes this works out pretty well, and sometimes not, depending on coax length and many other factors. The radials provide resonant lengths for this second half, and this helps to isolate the coax from working as part of the antenna. A vertical will work with only one radial, this antenna is called an L. By putting 2 or more radials evenly spaced around the vertical, it makes the patern more uniform. A mobile on the other hand is using the car body for the second half of the antenna. Just not all that practical to put resonant radials on a mobile.

OK if the vehicle is the other half of the antenna on a mobile where is the other half on a fiberglass boat? A Half Wave antenna requires No Ground Plane & why most marine antennas are Half Wave.I use a Larson 2/70 dual band mobile antenna on my pickup truck & it requires No Ground Plane yet it out talks the antennas that do require one? Something about the other part of the antenna being the vehicle does not compute & that short piece of coax on the antenna does not make it up either since the SWR is the same on my Antenna Analyzer on a 2 ft piece or the 18 ft piece & the same when I test my Antron 99 which does not have a ground plane kit?

SIX-SHOOTER

[Sandbagger]

Dec 30, 2018 12:20:48 GMT -5 SIX-SHOOTER said:

Dec 28, 2018 15:34:08 GMT -5 ytradio said:

It is the other half of the antenna, as in a dipole, which basically, all antennas are. Even though some antennas do not have radials, something else is making up the other half, usually the shield of the coax. Sometimes this works out pretty well, and sometimes not, depending on coax length and many other factors. The radials provide resonant lengths for this second half, and this helps to isolate the coax from working as part of the antenna. A vertical will work with only one radial, this antenna is called an L. By putting 2 or more radials evenly spaced around the vertical, it makes the patern more uniform. A mobile on the other hand is using the car body for the second half of the antenna. Just not all that practical to put resonant radials on a mobile.

OK if the vehicle is the other half of the antenna on a mobile where is the other half on a fiberglass boat? A Half Wave antenna requires No Ground Plane & why most marine antennas are Half Wave.I use a Larson 2/70 dual band mobile antenna on my pickup truck & it requires No Ground Plane yet it out talks the antennas that do require one? Something about the other part of the antenna being the vehicle does not compute & that short piece of coax on the antenna does not make it up either since the SWR is the same on my Antenna Analyzer on a 2 ft piece or the 18 ft piece & the same when I test my Antron 99 which does not have a ground plane kit?

SIX-SHOOTER

A boat antenna is a unique situation. It is common to see both 18' 1/2 wave CB antennas (Which could either be an end-fed 1/2 wave like an A99, or a coaxial center-fed dipole), or 1/4 wave mobile style antennas with a matching stub, which then uses the coax as the "other side" of the dipole. It's not the most efficient setup for an antenna, but it will work. At VHF frequencies, it's not difficult to make a practical dipole, or a colinear gain antenna.

[321 treeclimber]

My dad ,the "bilge rat" used to say it was the water. Marine antennas like the Shakespeare bigstik is a good example,no radials, not mounted that high and yet always great swr when on a boat.he said it was deflection off the water. Put your boat on a trailer in the marina and try it...not so good.that was our experience. 321 treeclimber

[Sandbagger]

Dec 30, 2018 20:19:53 GMT -5 321 treeclimber said:

My dad ,the "bilge rat" used to say it was the water. Marine antennas like the Shakespeare bigstik is a good example,no radials, not mounted that high and yet always great swr when on a boat.he said it was deflection off the water. Put your boat on a trailer in the marina and try it...not so good.that was our experience. 321 treeclimber

Well, back in the "old days" of 2 Mhz AM marine radios, they used to attach a copper ground plane to the hull which would couple the water (which was much more effective in salt water) to the ground side of the radio, and that improved the performance considerably as 2 Mhz radio signals have a considerable ground wave. It was not uncommon for us to be able to make contacts from Atlantic City New Jersey to New York, at night when the band went long with about 50 watts of power. CB frequencies are much higher and the effect of the ground wave is much less. Also, the Big Stick antenna did not require a ground plane to work. But having a body of water (especially salt water) under the antenna would improve the reflective nature of the ground plane counterpoise. Also a boat on a large body of water has virtually an unobstructed line of sight path to the horizon. On shore with buildings, trees, hills, etc, range will be less.

[321 treeclimber]

Popeye knew what he was doing....I'm still gonna try my tin roof. 321

[Sandbagger]

Dec 30, 2018 23:23:29 GMT -5 321 treeclimber said:

Popeye knew what he was doing....I'm still gonna try my tin roof. 321

A 102" whip at the peak of that metal roof should match well and present a good SWR. It should also radiate well enough due to the pitch of the roof. But the question remains whether that would be as effective a radiator as a gain-type ground plane antenna mounted 50' (or even 20') in the air. When I first moved into my present location, I ran a 102" whip mounted to the rain gutter on my 2nd floor. SWR was very good and it did work fairly well, as I was 400' ASL. But it wouldn't hold a candle to the Sigma 4 that I put up later on an 8' pole in the back yard.

I understand that people have budgets and not everyone can afford to construct the most optimal antenna system. But you should always try to get the best antenna setup that you can afford to get. Especially if your locals are not all that close and you want to be able to be heard consistently and comfortably. You are far better off with a cheap radio and a great antenna, than the other way around.

[321 treeclimber]

10-4 my current arrangement works well, sirio 1/2 wave at forty ft. And maco 5/8 4 radial ground plane with the tip at 70+ ft. I switch back and forth as if it made a real difference with different radios but they both work well. The sirio is a stick. There is an available ground plane kit I'd like to get.but my other property cabin roof is something worth experimenting with.

[Sandbagger]

Dec 31, 2018 12:34:38 GMT -5 321 treeclimber said:

10-4 my current arrangement works well, sirio 1/2 wave at forty ft. And maco 5/8 4 radial ground plane with the tip at 70+ ft. I switch back and forth as if it made a real difference with different radios but they both work well. The sirio is a stick. There is an available ground plane kit I'd like to get.but my other property cabin roof is something worth experimenting with.

Oh heck yea! If you're doing it just for the fun of experimenting and learning things, that's one of the biggest thrills in this hobby. I'd say go for it, and see just how each of your antennas systems compare. You'll probably find that no single one will be better 100% of the time. One may do better under one set of circumstances, while a different one works better under a different set of conditions. That's why a lot of hams have several different antennas, so that they can switch to the one that works best for each condition.

[321 treeclimber]

Thanks for the support. I am truly an over zealous novice in this realm and need all the help i can get.happy new year!

[321 treeclimber]

By the way, i just purchased a sirio 2016 5/8 ground plane. Will go up in spring. Really well made. 321

[ytradio]

Several people around me are running the Sirio Vector 4000 and are just crazy about it. The only thing I don’t like about it is that it does not seem to be very rugged. One fellow bought a damaged one and repaired it, and used it as a patern to build another from scratch, only out of heavier tubing and hardware. This past week his new one still received wind damage. It is a tall antenna. But I can say that they all seem to perform well.

[321 treeclimber]

Yeah 10-4 , i will say this; i always have 2 antennas in play.in a recent heavy wind event,i lost my antron to internal damage due to severe flexing and wind whip,looked like i had a marlin on the hook! But my sirio 27 took it no problem. This new 2016 5/8 is to replace the antron.i think they are well made.way better contruction than my macov58. 321