Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KC0BUS, May 28, 2019.
What kind of antenna would be used for 2-meters SSB mobile operation? Thanks
Something horizontally polarized, halo, squalo, turnstile, or something similar.
Other then “because we’ve always done it that way”, why?
A few reasons:
Because most everyone is still doing it that way.
Because it provides some isolation from vertically polarized FM traffic, reducing intermod and desense.
Because horizontally polarized signals suffer a bit less ground loss and they diffract over terrain and obstacles better.
Because it's easier to mount a beam antenna horizontally, since that places the mast out of the plane of the antenna.
The reason FM is normally vertically polarized is the need for omnidirectional mobile antennas, which are easier to make with vertical polarization.
It is not necessary to abide by the convention, but if you stray from it, you'd best agree with a group of your friends to stray from it together. You'll have trouble making contacts with operators using polarization orthogonal to yours.
By convention, as well as for good scientific reasons, all non-FM activity on VHF is generally horizontally polarized. FM is almost always vertically polarized. Theoretically, the cross-polarization loss between vertical polarization and horizontal polarization is infinite. However, in the "real world", this cross-polarization loss is generally at best 20 dB and, in some situations, can be even as much as 30 dB.
Using SSB, since the other stations are going to use horizontally polarized antennas, if the mobile were using a vertically polarized antenna, if the mobile was running 100-watts output, with 20 dB cross-polarization, the signal would be, at best, like the mobile was running 1-watt output and with 30 dB cross-polarization, the signal would be like the mobile was running 0.1-watts output (100 milliwatts). Since a mobile is almost always at a disadvantage even with proper polarization, having cross-polarization is going to have a serious effect on the performance.
Halo, "big wheel", etc., antennas are both horizontally polarized and omni-directional which is very beneficial for mobile operation. The "drawback" is that those types of antennas are considerably more difficult to build / install as well as, to many individuals, not all that attractive.
Back when AM was king on 2-meters, and there were a lot of Heath HW-30 "Twoer" units used mobile, there were several manufacturers building horizontally polarized mobile antennas as well as numerous magazine articles on building such. These days, such horizontally polarized antennas are pretty rare.
In the 60s used a 2-meter halo made by the same company in Fitchburg, Ma. that made the Saturn 6 for 6 meters. Worked rather well. Back then a bumper mount with a mast was a common method of mounting the antenna. Needless to say, there is not much opportunity for bumper mounting on modern vehicles. One approach might be to rig a mast to a trailer hitch. Pay attention to grounding. The photo is a more modern version of the antenna which can be found with an eBay search.
A little late getting back to this thread. Thanks to all who provided answers, in many cases more than I would have thought of!
Ok, so far the discussion has been civil, hoping it stays that way.
Cross polarization, the signals may start out horizontal or vertical and as long as the path is LOS will stay the way the started. Once they start bouncing off of things, like the ionosphere, they probably won't stay the way the were launched.
Now, since the original question was mobile SSB, we come to mounting the "halo, squalo, turnstile, or something similar" on a vehicle. Mount one of them to close to the body work you launch most if your signal straight up. Fine if you are working a geostationary satellite directly overhead. Not so great for working stations out near the radio horizon or beyond. So you mount the antenna up high enough the roof or deck lid don't act as reflectors. Now you are beating your antenna into every low hanging object around, especially if you use a 4X4 or a van for your rover.
Yes, much of the man made noise is vertically polarized, and AM modes are more susceptible to noise pulses. Horizontal does have some advantages for non-FM modes. I could offer that circular has advantages over horizontal. As does orthogonal. But those require more, shall we say, complicated antennas to launch.
Story time. Once upon a time long ago in a galaxy far away, it was noticed there was an opening over a water path. In his haste to make best of the opening the operator of a very capable VHF station suddenly noticed he was on his vertically polarized 2 meter beam. Thinking signals would improve he flipped his switch to the horizontal antenna. Signal strengths dropped by half. You see radio is as much art as it is science.
To the OP, as long as you are aware of the limitations, yes you can make VHF SSB contact on a vertical antenna. BTDT. No it is not ideal. It is doable.
So should I even consider mounting a halo antenna to a triple magnet mount (or quad magnet) and then sticking it to the roof of my car and expect even reasonably okay performance?
M2 is a respected designer of 2 meter antennas. Take a read here and make up your own mind. https://www.m2inc.com/FG2MHOLOOP