[Larsen Pulse 2/70 Sh]

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.

[GMRS on a Road Trip?]

The term legal is a misnomer. The correct question would be: is a given radio certified for GMRS operation. 

 

The specific requirement is stated in Part-95E

§ 95.1761 GMRS transmitter certification.

(a) Each GMRS transmitter (a transmitter that operates or is intended to operate in the GMRS) must be certified in accordance with this subpart...

If your radio is not GMRS certified then you are in violation of the rules. However, you are no more, or less, in violation than you would be if you did not properly identify.  Nobody can or should tell you it is ok to violate the rules, that is a decision you have to make for your self. However, I will tell you that many people have chosen to use high-quality non-GMRS certified (but often certified to the more stringent Part 90) equipment. I will also say, that there is no recorded case of anyone ever having been cited or punished for running Part-90 equipment on GMRS. In fact, there are no know citations for running any non-certified equipment on GMRS.

 

What I would advise is to always run quality equipment maintained in good working order and operate that equipment in accordance with the GMRS regulations.

 

Actually it seems Part 90 radios are OK to use on GMRS, this from my gmrs club:

 

Per n149 of FCC 17-57, the preceding serves to “clarify” the preceding/replaced 95.655(a):

– n149 Several commenters are concerned that the proposal to prohibit combination radios would prevent GMRS licensees from using surplus

Part 90 equipment in GMRS. ... This is not our intent. We will continue to certify equipment that meets the respective technical standards for

Part 90 (land mobile) and Part 95 (GMRS) in both services, if requested. However, we are amending the language in new section 95.1761©

to clarify the requirement in old section 95.655(a) that Part 95 GMRS radios will not be certified if they are equipped with the capabilities to

operate in services that do not require equipment certification, such as the Amateur Radio Service.

[Introduction to GMRS for new users]

Unless I missed it, the article is missing one important topic, which is using tones to open up the repeater receiver.
Some club repeaters can't be accessed or opened up without tx'ing the right DCS or CTCSS tone.

FWIW.