The usual convention is to use vertical polarization on FM and packet and horizontal polarization for CW and SSB. This is because you generally want repeater antennas to be omni-directional, vertically polararized to enhance the operating range of mobile and portable units using vertical whip antennas.
Horizontally polarized yagis are commonly used for weak-signal work on CW and SSB because they ARE directional, and are quieter because the don't hear signals as well which aren't in the direction of interest. Contesters like higher gain and a high front-to-back ratio and good side rejection, whereas a shorter antenna which is easily transported, with a wider useable pattern or an omni-directional loop are desired for rover/portable/mobile or net operations.
For FM simplex use in EmCom, most people use vertically polarized antennas, because they "dance with the girl they brought." Trying to work somebody who is cross-polarized with you results in about a 20dB signal loss so you may not be heard at all.
However, since most line and atmospheric noise is vertically polarized, horizontally polarized antennas have a lower noise level generally. This might have certain advantages for EmCom if everyone on the net was horizontally polarized for simplex operations. Many small 2-meter yagis of 3-5 elements with boom lengths of less than a wavelength are broad-banded enough to have a useable 1.5:1 VSWR bandwith which covers the entire 2 meter band. Horizontal loops are only unity gain, but are compact, easily stacked for gain, and while not full-band, they are at least useable up to about 146.5 MHz under 2:1 VSWR, so have possibilities.
In admittedly very limited tests on 146.415 FM simplex and 144.25 USB we made some antenna comparisons. I was in my mobile in Mills Gap, FM09 in 3-way QSO with my brother KE4SKX in Woodbridge, VA and KE4QMR, located in Fairfax, VA, both in FM19, roughly 80 air miles away. SKX and I both used Kenwood TM255A all-modes and KE4QMR used a Yaesu FT100.
In my mobile I alternated between two switched antennas, an M-Squared half-wave horizontal loop on 39" trunk mounted mast and Diamond SG7200 dual-band vertical whip, also on the trunk lid.
KE4QMR made comparions between a Custcraft AR-270 dual-band vertical and a KB6KQ horizontal loop switched on his apartment balcony.
My brother KE4SKX switched between 2-meter vertical hamstick with base station radial kit and a horizontal Cushcraft 124WB 4-element yagi, both antennas in his attic.
On SSB, when all were horizontal we had clear traffic-capable copy with good audio, but no S-meter reading at 5 watts. At 40w we all were solid S7-S9 signals. When vertically polarized we had only broken weak copy at 5w, and had to bump to 40w to have traffic quality.
When all were vertically polarized, we had readable but noisy copy on FM, as we expected. We've done this many times before and at that distance on FM everybody needs a beam for optimum traffic handling. That was no surprize.
But the real surprize came when I as a lark, I changed to the loop on FM and they all went horizontal to listen. I was able to work them from WV with only 5 watts, which we couldn't do with the verticals on FM.
Of course, this was only one test. It could have just been good band conditions or the luck of the blind monkey. It probably doesn't mean anything, but we all intend to experiment more with horizontally polarized FM on simplex. We are also encouraging more RACES operators to get all-mode 2-meter capability as an alternate to 75 meter phone for short path EmCom beyond repeater range.
This will enable us to use more uncoded techs in our statewide nets. It would simplify matters greatly to standardize on one antenna for portable kits. A two- meter horizontal loop is very compact and portable. It's isn't high gain, but seems to work very well. For now I'm carrying one in my "go kit" and mounting it 1/2 wave below my dual-band vertical on my portable mast kit.
I'd be interested in hearing from anyone who uses 2 meter SSB for ARES or RACES, or ragchewers who may have used horizontally polarized antennas for FM. We may learn something and come up with a new set of recommended practices. At minimum, it should be a fun discussion.
73 de KE4SKY
Virginia State RACES Training Officer