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Author Topic: How close can two antennas be?  (Read 6903 times)

Posts: 109

« on: September 10, 2013, 01:10:27 PM »

I'm about to put up a hexbeam antenna and the edge of the hexbeam will be about 20 feet away from my G5RV antenna. Do I need to have more separation between them?

Thanks and 73,


Posts: 2100

« Reply #1 on: September 10, 2013, 01:39:47 PM »

  FWIW, My Hex is 23 ft. high and I have a Windom type antenna about running about 4 ft. away at about 45 degrees below one of the one of the hex's spreader tips, no problem here.
« Last Edit: September 10, 2013, 01:42:25 PM by W1JKA » Logged

Posts: 568

« Reply #2 on: September 10, 2013, 02:28:33 PM »

As long as your SWR has not changed much, you should be OK. If there is any way possible, I'd try to get some more room between them if possible, but sometimes you just have to do what you have to do.
It may be causing some interaction, especially on the new one that you will have no idea of due to the fact that this is the first time it's going up, but like I said, if the SWR on both antennas is good, I have no doubt you'll get out.
I've got 5 antennas in my yard (Or will soon), getting space between them and having them all work as good as possible, buildings ect. can be a real pain sometimes.
I've got more room than most, but no tower can be put up and no trees, so it's tough on the lower bands due to height issues. I had to go to a vertical for the lower bands, but from what I've read on the reviews, should not be at much of a disadvantage.

73's John KF7VXA

Posts: 3541

« Reply #3 on: September 11, 2013, 06:34:26 PM »

The only way to know whether the two antennas can live near one another is simply to put them up and try them.  This isn't precision science; what works fine in one location might be terrible across the street.


Posts: 2566

« Reply #4 on: September 11, 2013, 08:27:16 PM »

I'm about to put up a hexbeam antenna and the edge of the hexbeam will be about 20 feet away from my G5RV antenna.

For the frequencies involved that is very close. Think of the G5RV as acting like a reflector or director on the hexbeam. I bet your antenna pattern will be really skewed. The thing is it is also going to very unpredictable depending upon antenna orientation, frequency and what is attached to each.

It may not matter to you but if I was spending that type of money on a Hexbeam I would try to keep it as free-space as possible so it can do its thing.

Also you do not want to have a receiver attached to the other antenna while you are using either one.

Some of the NEC folks can give you a better idea of the weirdness that can happen.

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f

Posts: 1050

« Reply #5 on: September 12, 2013, 03:07:31 AM »

It'll work just fine. It might not be as optimal as it should but it'll work OK. There's all kinds of metal in my garden my Hexbeam is probably coupling to from an inverted V 40m dipole to metal guttering on the house and even the wiring in the house and garage below it and the streetlamp nearby. I have no problem with it.

Whilst AA4HA is correct in that you want it in as free space as possible, for most amateurs unless they have the ability to stick such an antenna on a 60ft tower in the middle of nowhere with nothing within a few 100ft of it in all directions its going to be coupling to something.

Posts: 1850

« Reply #6 on: September 12, 2013, 06:45:59 AM »

My Hex Beam is not terribly far from the end of a W5GI (similar to G5RV), tuned for 20 m, and I don't notice any adverse interaction. There will not doubt be significant coupling, but I've not noticed any problems. My station is set up so I can only have one (of five) transceivers connected to any one (of seven) antennas.
My doublet antenna runs over the top of my top loaded 160 m vertical. I find I need to tune the coupler on the doublet for 30 m to realise the best match on the 160 m vertical. I must have had the doublet tuned to 30 m, when I tuned the L-match on the vertical.
Probably the best way to minimise coupling between antennas is to have them end on to each other, or perpendicular. This is something I've discovered on DXpedition, with multiple stations operating on the same site. The worst is two dipoles parallel to each other, or two verticals. Dipoles should be end to end, or perpendicular to each other. A vertical on the beach, with a dipole end on to it can work very well together. In fact, we were able to run CW and SSB stations concurrently on 10 m. Multiple multiband antennas can be troublesome for interstation interference. We use remote couplers at the base of verticals and a balanced coupler for the dipole.
Another strategy is to switch in a capacitor or inductor in an antenna not being used to detune it, to reduce interaction with the active antenna.
Luke VK3HJ

Posts: 109

« Reply #7 on: September 13, 2013, 07:22:24 AM »

Thanks for all the information. This will help greatly.



Posts: 501

« Reply #8 on: September 13, 2013, 12:19:04 PM »

My Opinion and observed facts:  Opinion based on the following facts - will not and have not burned out any receiver front ends, or seen degraded performance, even with a 15 foot antenna separation distance in my small city tract lot. 

Measured Experimental setup:  I have BW65 folded dipole, CHA250 vertical, Zero - Five 17 meter 5/8 wave monoband-er vertical, PAR END FED - SWL only long wire, 2 A-99 10 / 12/ 15/ 17 verticals , and a 6 meter Ground Plane (as well as numerous VHF/ UHF/ Microwave antennas) all within about 10 -15 feet of each other in my small city tract lot house.  I run 500 watts on HF 3.5 to 30 MHz into the  BW65 and 18 - 30 MHz into the A-99's no problem.  I did measure the "pickup power intensity" in the antennas set as receiver antennas measured using my GW INSTEK GSP-830 Spectrum Analyzer.  Note there is unspecified cross polarization path loss.  As such, I measured the following:

Test Frequency:  14.340 MHz
Mode:  CW
Power:  500 watts into BW65 antenna
Antenna separation:  15 feet
Cross polarization:  Yes

≈+20.8 dbm    which is ≈+121 dbµv     which is ≈120 milliwatts

Front End Burnout is not specified on any rigs.

NONE of my rigs experience any Front End degradation or burn out and without doing a detailed front end analysis, I suspect that with today's high IP3 points of +40 dbm (10 watts), I am hard pressed to ever burn out any of my receiver front ends at 15 feet separation. 

Now moving closer or TOUCHING, that's another matter entirely.  Certainly touching would likely lead to catastrophic front end burn out.
Bottom line:  Are there any close field SWR effects?  Probably and is that a big issue, NO, its not worth worrying about.  Are there any burn out problems?  NO from the above data.  Therefore, I continue to operate full 500 watts and leave all other receivers, transceivers connected to their respective antennas in my yard with zero degradation or burnout problems, now for well over 2 years.  ITS NOT A PROBLEM!


Posts: 500

« Reply #9 on: September 15, 2013, 05:13:30 PM »

I'm about to put up a hexbeam antenna and the edge of the hexbeam will be about 20 feet away from my G5RV antenna. Do I need to have more separation between them?

Thanks and 73,

Ok, 20 ft away.  But will they be at the same height?

When I lived in Georgia I had two fellow ham roommates.  We each had our own HF (wire and/or beam) and VHF antennas,  Very seldom did the three of us operate at the same time and when we did I don't recall any problems.

« Last Edit: September 15, 2013, 05:20:11 PM by KD4LLA » Logged
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