-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
isolation from mast
- Thread starter Splash1
- Start date
Slash1, IMO because the design of the A99 for one, the one that probably generated the concerns, causing the ideas of isolation to be a current day topic of discussion, was designed as a compromise idea with a special purpose in mind.
Isolation is an idea to improve the effectivness of raised vertical antennas with a scheme to improve the affects of the attached ground plane.
The A99 produced the results the manufacture wanted perfectly in the day. Some say that Solarcon left the other half of the antenna off on purpose---just to make money. Even if that were true, and I don't believe it was, such an idea completely misses the point of why the antenna was likely designed as it was---to be safer, have a small profile, to be unobstusive, with a very small footprint, easy to install, handle, and tune.
B
BOOTY MONSTER
Guest
I think this mast isolation idea originated from the J-Pole. The J-Pole is a unique design that inherently wants to radiate off it's coax and mast. Amateurs have long written about the use of coax baluns and insulating from the mast with the J-Pole. With this in mind I feel it really depends on the type of vertical you use as to if insulating from the mast will help or not.
From a design standpoint, most end fed fiberglass verticals already have a balun installed as their matching network. This device serves two purposes. First it matches the impedance. Typically from few thousand ohms back down to 50 ohms. Second, it gives us the benefits of a balun and reduces common mode currents on the coax feedpoint ground.
This is also the mast ground and the location you would connect the optional ground plane kit. If the antenna has been specifically designed to operate without a ground plane, then there is going to be little current available here to see much benefit in the ground plane kit or mast isolation. This is not to say that it can't help at all and that some won't see a benefit. Because the internal balun will never remove 100% of common mode currents.
In cases where your mast is resonant at the operating frequency, you probably can see a reduction in RFI with mast isolation. In most cases with some care taken in the installation you can avoid having to insulate the antenna from the mast on most verticals except perhaps the J-Pole. If your antenna does not use 1/4 wave radials, a coax balun can only help with RFI problems.
From a design standpoint, most end fed fiberglass verticals already have a balun installed as their matching network. This device serves two purposes. First it matches the impedance. Typically from few thousand ohms back down to 50 ohms. Second, it gives us the benefits of a balun and reduces common mode currents on the coax feedpoint ground.
This is also the mast ground and the location you would connect the optional ground plane kit. If the antenna has been specifically designed to operate without a ground plane, then there is going to be little current available here to see much benefit in the ground plane kit or mast isolation. This is not to say that it can't help at all and that some won't see a benefit. Because the internal balun will never remove 100% of common mode currents.
In cases where your mast is resonant at the operating frequency, you probably can see a reduction in RFI with mast isolation. In most cases with some care taken in the installation you can avoid having to insulate the antenna from the mast on most verticals except perhaps the J-Pole. If your antenna does not use 1/4 wave radials, a coax balun can only help with RFI problems.
HiDef, I might agree with you that isolating antennas from the supporting mast is unnecessary, but depending on the magnitude of common mode currents in the system, isolation can and does show me some improvements in signals when I did it to an A99 recently.
I don't see as much improvement as some others that I know who have tested this idea of isolation and posted results right here on WWRF. In this case however, I think it is because the soil here on the Gulf Coast of Texas is very high in conductivity---and I believe that minimizes the ground affects on the antennas somewhat, so the differences I see are very minimal.
But, for you to say this idea is BS is being a bit categorical in your claim. So, I guess I have to ask what is the bases for your claim here?
If you are interested I can supply the support for my idea that you could consider as my argument, but I don't think it will change your mind. This is just to let you know that I have something available to support my ideas other than just words.
How say you?
Hi Marconi,
If the antenna has a common mode current condition it needs a resonant counterpoise. The counterpoise can be in parallel with a mast. The antenna not be isolated.
There are sleeve dipoles with sleeves of inadequate diameter at the end. Isolating one of these will actually change the resonant frequency. The proper fix is to either add a set of radials or correct the sleeve.
Isolation as described here will also require a balun and again will require retuning of the antenna if common mode rejection had indeed been achieved.
I've seen mis application of internet information posted on quite a few radio forums. At CB frequencys the ground isn't going to mean much for fixed antennas as the antenna is usually elevated by at least one wavelength. Still some will paste a chart from Rauch's site that shows ground effects at 7 mhz and expect it to be similar for 27 mhz.
Tens of thousands of Radio shack 1/4, 1/2, 5/8 and other brand antennas were sold and used over 30 years ago with that very setup. Radials and mast bonded together. CB used to be big business and any antenna with a slight advantage over this would have sold well.
The original Ringo Ranger had a common mode problem which was fixed by adding radials. Tuning was quite a bit different before and after.
The R.F. current pickup posted here a week or so ago would not be usable for before and after measurements on a CB antenna. Careful reading of that text shows why.
As for people posting results, you know and I know there are lots of people who want to see a payoff so badly that they probably CAN hear less static or whatever else they are looking for. Emperor's clothes.
Just look at the audiophile sites for proof positive that baloney brings results.
I'm not here to sell anybody anything. Consider that. Others are. That makes a big difference. You can just see them looking for a mark. Find someone to believe the religion and you have a customer through thick and thin. Read: Fat Boy Technology.
I'd like to see your measurements and measurement methods. It would be a great exercise. Nothing would be better than to prove me wrong because then I'd learn something new.
If the antenna has a common mode current condition it needs a resonant counterpoise. The counterpoise can be in parallel with a mast. The antenna not be isolated.
There are sleeve dipoles with sleeves of inadequate diameter at the end. Isolating one of these will actually change the resonant frequency. The proper fix is to either add a set of radials or correct the sleeve.
Isolation as described here will also require a balun and again will require retuning of the antenna if common mode rejection had indeed been achieved.
I've seen mis application of internet information posted on quite a few radio forums. At CB frequencys the ground isn't going to mean much for fixed antennas as the antenna is usually elevated by at least one wavelength. Still some will paste a chart from Rauch's site that shows ground effects at 7 mhz and expect it to be similar for 27 mhz.
Tens of thousands of Radio shack 1/4, 1/2, 5/8 and other brand antennas were sold and used over 30 years ago with that very setup. Radials and mast bonded together. CB used to be big business and any antenna with a slight advantage over this would have sold well.
The original Ringo Ranger had a common mode problem which was fixed by adding radials. Tuning was quite a bit different before and after.
The R.F. current pickup posted here a week or so ago would not be usable for before and after measurements on a CB antenna. Careful reading of that text shows why.
As for people posting results, you know and I know there are lots of people who want to see a payoff so badly that they probably CAN hear less static or whatever else they are looking for. Emperor's clothes.
Just look at the audiophile sites for proof positive that baloney brings results.
I'm not here to sell anybody anything. Consider that. Others are. That makes a big difference. You can just see them looking for a mark. Find someone to believe the religion and you have a customer through thick and thin. Read: Fat Boy Technology.
I'd like to see your measurements and measurement methods. It would be a great exercise. Nothing would be better than to prove me wrong because then I'd learn something new.
Last edited:
I lifted my gp off it's pole today and the ground interference was noticeably reduced.
More than half.
More than half.
I was surprised to see some improvement in my A99. I think isolating the antenna helps. I didn't see as much as Bob and Multimode 200 have in the UK, but I didn't isolate the antenna the same way either. I just isolated my mounting brackets with PVC at the clamps and Bob and Multimode 200 isolated theirs by raising the radiator up well above the mast, which likely provides better. I hope to try that idea soon.
Last edited:
- No one is chatting at the moment.
