Lowband antenna ground plane

[flythunderbird]

All,

If I may, I'd like to ask a question about ground planes for lowband antennas. There's still some lowband traffic in my area, and I'd like to see if I can pick up any skip. I'm putting together plans for a tilt-over mast to be used with my scanning station, like the one tonsoffun has in the wiki:

Tilt-over mast

with separate antennas for lowband, VHF/UHF, and 800MHz. I already have a DPD Omni-X for VHF/UHF. Use of the forum search indicates that good choices for lowband antennas are limited. I found prcguy's excellent article on the Austin Spectra vs an A/S MON52 and a broadband military antenna:

Military vs scanner antenna

and, after studying his article, thought I might try to find a surplus military antenna. Well, the radio gods have smiled upon me and I've found a complete Harris RF-3183 in good shape. For those who aren't familiar with it, these antennas are used on HMMWVs and other military vehicles:

Harris RF-3183

I read on another site that the RF-3183 doesn't actually require a ground plane to work, but I'd think that performance would be compromised. So my question is:

Given that this is for lowband, what form of ground plane should I use for this antenna? I was thinking about adapting the correct HMMWV vehicle mount for use on the mast and adding some sort of a ground plane. I'm not crazy about four 8-foot radials, so I was wondering about chicken wire or something else (my backyard isn't that big). Would it be better to fab up a mount and put it on the roof of my garage? I don't have any problems with doing that. Or is there an altogether better alternative?

Please note that I'm not necessarily stuck on this antenna. Things are in the planning phase at this point, so if there is a better alternative, I'd love to hear about it.

Any and all comments, suggestions, pointers, etc. are welcome and desired. Thank you for any assistance you can provide.

 

[trp2525]

...Or is there an altogether better alternative?

Please note that I'm not necessarily stuck on this antenna. Things are in the planning phase at this point, so if there is a better alternative, I'd love to hear about it.

Any and all comments, suggestions, pointers, etc. are welcome and desired. Thank you for any assistance you can provide.

Antenna Specialists made a MON-4 VHF-Low (25-50 MHz) ground plane antenna many years ago. They occasionally pop up on eBay, Craigslist and/or at estate sales. Being a single-band antenna, it was EXCELLENT on VHF-Low.

 

[Ubbe]

I read on another site that the RF-3183 doesn't actually require a ground plane to work, but I'd think that performance would be compromised.

It's a multiband antenna that already are compromised to make it work on all bands and if you use a groundplane, and you should, it probably has -5dB loss, as they state are its lowest "gain", in relation to a standard 1/4 wave single band GP antenna for low band. You can probably build a GP yourself using 2 meter long elements or perhaps a dipole might be easier to build and use a 75/300 ohm balun to make it more broadbanded like a ST-2 on low-vhf.

/Ubbe

 

[mancow]

I hand one of the Harris antennas. I would have to look again but I think the instructions said it needs a 10 ft groundplane.

 

[prcguy]

If you look at my article on military vs scanner antennas you'll see the specific Shakespeare SF-3512 I used for comparison has about 7.5dB more gain than the AS MON-52 series at resonance around 33MHz, and out of resonance the military antenna can pull ahead by 30dB or more across the 30 to 50MHz range. That is not a subtle improvement and more of a smack you in the face why isn't my AS MON series working today kind of difference. You have to remember that scanner antennas that cover VHF lo band will be tuned to one specific frequency and everywhere else they will not work very well, where the military antenna covers the entire range and more.

Most of the multiband military antennas need a ground plane and a continuous one at least 1/2 wavelength in dia at the lowest freq (30MHz) would be ideal, but for base station use the military seems to use three or four sloping radials around 5ft long for convenience. There is nothing special about them sloping and they do that to make a tripod so the antenna can sit on the ground.

The bottom line here is the 9ft range multiband military antenna will seriously spank any other scanner antenna in the VHF lo range and it will also hold its own throughout the entire range through 512MHz in most cases.

Edit: If you can find the old Viet Nam War vintage AS-1729 vehicular antenna, its a vertical center fed dipole that covers 30 to 76MHz with a switched matching box at the base. These work quite well but you have to manually turn the switch in the base to change frequency range, or make up a cable and a box with switching to be able to switch change remotely. I have one of these somewhere I might put on Epay and they are fairly common on the used surplus market.

 

[Ubbe]

You can see at Harris website that the antenna, as almost every antenna, have its lowest gain at the lowest frequency and this particular antenna says on the website has -5dB as it lowest gain value relative to a 1/4 wave element. So skip that Harris antenna and get something else like that great performer Shakespear.

I did a measurement today and a balun connected to a 460MHz dipole changed a +/-10Mhz bandwidth of the antenna at the SWR 1,5:1 points to +/-20Mhz. I have to do some outside listening tests to be able to know what happens to the gain at a horizon angle.

/Ubbe

 

[prcguy]

The Harris multiband antennas are usually off the shelf models from Comrod and similar to this one: https://www.comrod.com/wp-content/uploads/VHF30512CEF.pdf The Shakespeare SF-3512 is lossy at best but all of the scanner antennas that cover VHF lo are so lossy that the military versions have more gain and also work more consistently across the entire VHF lo band.

You can see at Harris website that the antenna, as almost every antenna, have its lowest gain at the lowest frequency and this particular antenna says on the website has -5dB as it lowest gain value relative to a 1/4 wave element. So skip that Harris antenna and get something else like that great performer Shakespear.

I did a measurement today and a balun connected to a 460MHz dipole changed a +/-10Mhz bandwidth of the antenna at the SWR 1,5:1 points to +/-20Mhz. I have to do some outside listening tests to be able to know what happens to the gain at a horizon angle.

/Ubbe