6m (tri-band) mobile antenna on a fender mount

[montyhouse]

I'm purchasing a Comet SBB-15 tri-band (6m/2m/70cm) to use both as a remote campsite base antenna on a mast and hopefully for my truck's fender mount. Has anyone had experience with how 6m performs on that type of mount?

 

[vagrant]

A 1/4 wave antenna performs best with an appropriate ground plane for RX and TX. Top dead center of your roof would be best for omni. If it is above your hood, it will favor the direction where it has more of the hood. If you're going to put it on a back fender...set your expectations to terrible and enjoy whatever you get.

I would not use that antenna on a mast without an appropriate ground plane underneath it, or either a counterpoise or multiple wires in a radius. Perhaps use a very large/strong magnet mount and place it on the top of your vehicle roof for mobile. When at the campsite leave it on the roof and run the coax to your tent or table.

 

[montyhouse]

A 1/4 wave antenna performs best with an appropriate ground plane for RX and TX. Top dead center of your roof would be best for omni. If it is above your hood, it will favor the direction where it has more of the hood. If you're going to put it on a back fender...set your expectations to terrible and enjoy whatever you get.

I would not use that antenna on a mast without an appropriate ground plane underneath it, or either a counterpoise or multiple wires in a radius. Perhaps use a very large/strong magnet mount and place it on the top of your vehicle roof for mobile. When at the campsite leave it on the roof and run the coax to your tent or table.

Roof and tailgate are, unfortunately, not options for me, so if it's not working, I'll switch to a smaller dual band (e.g., Tram 1181) on the fender mount and give up on 6m in truck. Posted regarding using that antenna as a campsite base here with Tram 1465 mounting bracket and longer radials (four 1/8" aluminum rods @ 60" each) to give it a better chance at 6m.

 

[KK4JUG]

I encountered the same problem. The Yaesu FT8900 in my SUV has 6m capability but I don't use that band now. Overcoming antenna problems for 6m was more trouble than it was worth. I had purchased a Diamond CR8900 antenna which, I assume, was made specifically for the radio. Then came the problems. First, the antenna is 50" long which would be unwieldy on top of any vehicle. Second was the need for a great ground plane.

The radio also has .70m, 2m and 10m. Because of the antenna problems I mentioned earlier, I elected to use it for .70 & 2m only. I still have the antenna still in the plastic as well as the original shipping box.

 

[west-pac]

When that radio came out decades ago, I felt it was mostly a gimmick. Granted, there are 6m and 10m FM simplex and repeaters, but using those in a mobile environment is not ideal because of the antenna size. From my experience most 6m and 10m activity is on SSB anyway. An 8900 would be okay if you wanted a shack radio to monitor for 6m and 10m FM and SSB openings, as well as having 2m/440 FM radio.

As far as any radio antenna on a vehicle, its going to be a compromise regardless, and ANY antenna is better than NO antenna. So if you have a 6/2/440 radio and antenna...Go For It! You may catch the next best FM opening from that NYC repeater ((or is that on 10m?)).

 

[KK4JUG]

When that radio came out decades ago, I felt it was mostly a gimmick. Granted, there are 6m and 10m FM simplex and repeaters, but using those in a mobile environment is not ideal because of the antenna size. From my experience most 6m and 10m activity is on SSB anyway. An 8900 would be okay if you wanted a shack radio to monitor for 6m and 10m FM and SSB openings, as well as having 2m/440 FM radio.

As far as any radio antenna on a vehicle, its going to be a compromise regardless, and ANY antenna is better than NO antenna. So if you have a 6/2/440 radio and antenna...Go For It! You may catch the next best FM opening from that NYC repeater ((or is that on 10m?)).

You're right. The 8900 is a quad-band radio. Another couple of inches on the quad-band antenna and I could use it as a fishing rod. I live in the south and we have lots of trees, i.e., lots of things to hit the antenna. Actually, I already use two antennae. When I'm in town, I have a short antenna (c. 25") and on the road I use a longer one (c. 38"). Maybe I'll switch to the "fishing rod" for road use and take advantage of the 6m stuff out there.

 

[jhooten]

A funny thing about the Diamond CR-8900 antenna can be found if one takes the time to read the manual:
"INSTALLATION INSTRUCTIONS
NOTE: THIS ANTENNA REQUIRES TUNING TO DESIRED FREQUENCY. USE QUALITY VSWR METER
TO INSURE PROPER ADJUSTMENT. THE CR8900A REQUIRES PROPER VEHICLE GROUND.
MOUNTING LOCATION WILL AFFECT VSWR. NOT RECOMMENDED FOR MAGNET MOUNTS OR
MOUNTING IN CENTER OF ROOF."

"(2) Choose desired mounting location to insure maximum strength of mount, and proper vehicle ground to yield best
performance of antenna. NOTE: MATCHING NETWORK IS COMPENSATED FOR TRUNK LIP MOUNTING
AND IS NOT RECOMMENDED FOR CENTER ROOF MOUNTING."

(Bold added)

https://www.diamondantenna.net/pdfdocs/CR8900A.pdf

Another self induced problem with the CR-8900 comes when the buyer tries to cheap out ordering it from one of the discount sellers in Asia. The problem is they get a version of it that is tuned to the Asian bands for 2m/70cm not those in the US. Since moving the tuning tip only effects tuning on the 10/6m bands the antenna returns a mismatch on the higher two bands. Then the buyer goes on the various amateur web sights to proclaim the antenna to be a POS.

 

[KK4JUG]

I still have that instruction sheet. In addition, I have the Allen wrench and the extra tip that came with the antenna. I was aware of that stuff which is why the antenna has sat in the closet since I bought it. I would never call it a POS because I haven't been able to properly install it. I don't really know whether it works or not. I have the necessary meters, etc., to check it out but I don't have a suitable place to put it. I probably should have returned it to Giga Parts way back when.

 

[mrweather]

So the CR-8900 was designed from the beginning with the expectation that hams would use lousy antenna mounts? That’s unfortunate.

I had a similar experience with a Maldol tri-band antenna. Attached it to either my permanent roof or trunklid NMO mount and could not get the thing to tune on 6m FM (2m and 70cm were fine). Tried it on a L-bracket NMO on the quarterpanel and worked. So confused!

 

[jhooten]

Mine has survived on the trunk lid of two cars, a hatchback, the hood of a truck, and the rear of an SUV, so far. Yes it is a compromise. But it works.

 

[montyhouse]

The Comet's tuning options are, well, limited.

The SWR on a single band antenna can be adjusted by adjusting the length of the antenna to compensate for the difference in impedance provided at each mounting location. Not so with dualband or triband antennas, the power feeding coil is pre-set at the factory.

If the SWR is elevated, adjust the antenna location until you find the the best SWR.