Lscott

Yes some people do get it confused. What I'm looking for is the equivalent of a 1/2 wave antenna, thus no ground plane is normally required. The Comet CA-2x4SR does require a ground plane as I suspected from my testing. I confirmed this the other day by contacting Comet tech support. The reply I got is quoted below. "The CA-2x4SR is a 5/8 wave, so yes it must have a ground plane underneath the antenna in order to work properly. It was designed to be installed on sheet metal, like a vehicle trunk deck, hood, or even hatch back door. You need about 20” radius of metal under the antenna, but rarely is it possible to create a ground plane that provides the impedance needed at the antenna feed point. If you can use one of our lip mounts attached to the door edge, or hood edge to provide the ground plane." From my SWR scans you do need a really good ground plane. A magnet mount sort of works but a good direct electrical connection to a ground plane, or set of correctly cut to length radials, works even better from what I see.

Just and update I got an email from Diamond Antenna this afternoon. They have a new product in the works. This was the info I was sent below in quotes. "We will have the NR240A in a couple of months. This antenna, when on a mag mount is 140MHz-170MHz and 430MHz-470MHz. When it is grounded on a hatch/lip mount it is 140MHz-165MHz and 440MHz-465MHz. " Looks close to the spec's for the Comet wide band antenna. If the above is correct it seems the antenna is optimized for a wider bandwidth using a magnet mount? That is unless they got the magnet mount verses the hatch/lip mount bit swapped. Either way it looks like there will be an alternative antenna. I just wish it didn't require grounding. More new vehicles have plastic body panels so grounding gets harder to do.

I'm sure you're right. This was the point of asking. I did send an email off to Diamond Antenna a few days ago asking if they even offer anything like the comet CA-2x4SR. Never got a reply to date. I wish Comet still made the CA-2x4MB. The only failing was the spring for the fold over feature lost tension so the antenna would lift out of the socket then flip over at highway speeds. I had to wrap several layers of tape around that area to stop it. Other than that it's worked fine for years. I haven't had any issues with loose hardware, screws, or rust. If anybody has any interest I have the AA-1000 SWR scans of the CA-2x4SR on the roof of my Jeep using a 5 inch magnet mount and inside the house using a home brewed mount with 4 drooping radial elements, which gave the lowest SWR scan curves, much better that the specs in the Comet datasheet. I was rather pleased to see that. For the moment I can't seem to attach any files to upload. The message says I only have 666 bytes left. Not sure why it's still limiting me or is there a time limit that has to expire first before the upload limit is reset.

I can't seem to add any more files at the moment showing the scans for the Ham 2M and 70cm bands, which look just as good. The stated antenna gain is 4.5dbi from 145-148 and 7.7dbi from 440-450 with an SWR of less than 1.5, the graphs in the datasheet show over the above range a max SWR of 1.2. The antenna is about 59 inches in length, a big one.

I've been looking for a good dual band ground independent antenna for both the HAM 2M/70cm band and the MURS/GMRS bands. I have a new Comet CA-2x4SR antenna, which works, but requires a good ground plane. I don't want to drill any holes and the coupling with a magnet mount results in higher SWR, but still usable. I have an old Comet CA-2x4MB which is ground independent but hasn't been manufactured in years. I would like to find something like it. I recently did some SWR scans using a Rigexpert AA-1000 antenna analyzer, got similar results with spot checking using an old MFJ-269 as a sanity check, to confirm the performance. The antenna is mounted on a luggage rack using a Diamond K550KM rack mount kit on a cross rail on top of a Jeep. The scans all look very good for a large high gain antenna.

This point is interesting. Consider the following. I have a Kenwood TK-370-1 (wide band only) and a couple of Kenwood TK-370G-1 (wide and narrow band) radios. Both by the way are certified for Part 95 by the way. The TK-370-1 has an FCC ID of ALHTK-370-1 which shows a Part 95 certification. The TK-370G-1 has an FCC ID of ALH29473110 with a Part 95A certification which under the old rules was GMRS. You will also notice both radios also have a Part 90 certification too. Both radios have a stated spec of 450 to 470 MHz frequency range but will program down into the upper section of the Ham 70cm band, 440 to 450 typically for the main FM operations, and will work there. Since nether radio was physically modified, which would invalidate the certification, just programmed for both services, the FCC should not have a problem with using the same radio for both services. Hams are allowed to use radios for other services on the Ham bands so long as they meet emission requirements. So the point here is if you want to have access to both services you need to look very carefully for radios that have the Part 95 certification and can be programmed for the Ham 70cm band. With a Part 95 certification in addition to the Part 90 which should not be a disqualification.

The user programming software can be used to unlock the frequency range. At least it does on the Amateur version of the radio. Mine came locked to the Amateur Bands only out of the box. Click on the "Frequency Range" tab on the left side of the TH-8600 programming software. You should then see a small window with 3 frequency ranges on the left side, 150M 250M 450M. If you click in any of the ranges to the right you can't change the settings. Now press the "P" key on the computer keyboard. This NOT documented anywhere. Now you should get a small edit box that opens on the bottom of the frequency range window to enter a code. Type in "8600TH" without the quotes and is case sensitive. Then click "Enter". You should be able to click in any of the frequency range boxes now and change the values. Next write the code plug to the radio. Once this was done on mine I've never had to go back and change it. I can't say if this will work for the GMRS version of the radio but if somebody has one and wants to try it then let us know.

PastorGary, Thanks for the info. I wasn't sure if the radio was legal to use on MURS. There isn't a definitive clearly stated policy from the FCC I could find that states any Part 90 radio with a grant date before the creation of the radio service MURS or GMRS would be legal to use with the right programming to comply with the rules. That seems to be implied in the rules for the service in question. A bit off topic but I also have the older TK-370, not the "G" version, programed for GMRS. It has only 32 channels and wide band only. The radio has an FCC grant for Part 95, FCC ID ALHTK-370-1. I have it programed for the 22 GMRS simplex channels and 8 more for repeaters use leaving two spare. The FRS channels are programmed for RX only, 8 to 14, since they are narrow band only. The audio volume will be low but usable. The only issue with that radio is the antenna connector is the Motorola MX type. I think the newer one uses the same reverse SMA antenna connector as the TK-270G and the Chinese radios. I found an adapter that will convert from MX to female BNC for using an external antenna. FCC Grant TK-370-1.pdf

I've looked around but can't find any hard info for old Part 90 radios that are legal to use for MURS. For example I have a TK-270G HT purchased at the Dayton Hamvention. The FCC ID is ALH29463110. The grant is dated 10/25/1999 which is before the creation of the MURS service in 2000. If I read the rules and understand them it should be OK as long as the radio is programed to conform to the rules. Anybody else have a source for info on this topic? TK-270G-1 FCC - OET EAS Form 731 Grant of Equipment Authorization.pdf