so I just compared today my Larsen 2/70SH vs a Comet 2x4sr, both using the same NMO mount, center truck roof, brought down to the radios by LL-195 cable, good connectors. The comparison method was a passive field strengh meter whose antenna was tuned at 1/2 wavelength of GMRS at 467MHz, since that is roughly the repeater input frequency of interest. The field strength meter was not touched except to slightly move it around in case of a local null/peak that might bias the test. No such effect was observed. Basically the Larsen put out so much less power than the Comet, as witnessed by the field strength meter, it was shocking. Even at 440MHz, and adjusting the field strength meter antenna to closely match the 440MHz wavelength, the meter needle would barely move, whereas with the Comet and that same field strength sensitivity setting, the needle would nearly get pinned to 100% on 440 and 467. I had to check the Larsen at 2m to make sure something was not messed up, and at 144MHz, the meter needle would response well so the Larsen antenna is 'working'. The Larsen in this setup had decent SWR in VHF, UHF and GMRS bands, so it reminds that SWR doesn't mean that all that forward power gets transmitted as effective RF energy. The only variable again, in my test, was one antenna vs the other. All cabling, radio tx unit, all the same. In terms of real world performance, the Larsen on UHF 70cm stations, well I can hit them all well, and hear them well, but in terms of comparative EIRP, the Comet smokes it in the UHF department. The Comet is also alot longer and I simply can't use it on my roof as the antenna would have to be taken down (using the hinge) which is a hassle that I put up wtih for a while, but even though the Larsen is less efficient at 70cm, it doesn't require me to get my lazy butt out of the truck to garage the vehicle. The antenna bends nicely and snaps back as it drags under the raised garage door. But If I need maximum GMRS performance or UHG performance, I know where to put the Comet and switch cables etc to achieve maximum performance. p.s. right now the Comet is on the back right corner of my bed, mounted in a modified Breedlove mount (I replaced Breedloves connector since it seems to increase SWR) with an ARCANTENNA NMO LL-195 cable kit. That surprisingly puts out 50-60% of the power that the Comet does on the roof center NMO. HOWEVER... that does not hold true in front of the truck... the cab not surprisingly kills alot of the signal, so if you need to operated GMRS with a Comet in such a position, make sure your repeater is behind the cab basically.
