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9/22/2017 12:11:25 AM
Posted: 3/12/2006 5:56:02 AM EDT
Boy, I bought a Yaesu 7800 a few weeks ago and installed it in my mobile. A buddy of mine who is an RF engineer for FPL drilled an NMO mount hole, ran feedline etc, did an excellent job, but that has nothing to do with my issue.

I bought a MaxRad 2m/440 NMO antenna to go along with the radio, but after my signal reports, it seems like I bought a coil equipped dummy load.

Any recommendations for a new antenna?

I'm looking at those diamond fold overs currently, they seem to have a decent amount of gain.
Link Posted: 3/12/2006 6:06:48 AM EDT
[Last Edit: 3/12/2006 6:09:01 AM EDT by mr_camera_man]
I'm a newbie no-code tech myself, so take my words with a pound of salt. I'd start by taking a good long look at the mount, making sure that it's secure and well grounded. Maybe the next step would be to get a cheap 2m Hamstick antenna and see if the condition improves. If not, then you're only out $10-15 for the antenna, and you know that you get to have fun chasing cable or grounding issues.

Try posting this in the survival forum, where more of the hams seem to congregate.

Edit: 87 billion good antenna reviews
Link Posted: 3/12/2006 6:41:58 AM EDT
[Last Edit: 3/12/2006 6:53:33 AM EDT by Derek45]
Pull the coax from the rig, use an ohm meter to check for a short between the outer shield, and the center conductor. try it without the antenna installed on the NMO mount.

the meter should read an open.

Next check to see if the surface that the NMO is mounted to is actually ground.

I had a ford ranger that needed every damn piece of sheet metal bonded to ground, they must glue them together after they coat them, because nothing seemed to be tied to ground.

Ideally, the outer shield, and the ground of the vehicle should be a solid short on your ohm meter. in other word, the outer shield should be ground.

I like to ground the chassis of the radio, and run 12v fused wiring directly to the car battery.

What kind of car is it?

mr_camera_man's idea of trying a different antenna is a good one.

Have you used the radio elseware with good results?

I have owned a ton of YAESU's over the years, with great results, but the last 2m/440 mobile was a lemon that got returned to the dealer.
It was a piece of crap.

Also, if you have another radio, even a handheld, try it on your new car antenna and see how it works.

If the coax tests OK, see if you can beg/borrow/steal another dual band NMO antenna for a quick test. mount it on the existing NMO mount.

That will help you isolate the trouble.

If You can borrow a VHF/UHF SWR meter, that would be a big help. if you've got high SWR, you can damage the rig.

Good luck.

Link Posted: 3/12/2006 6:52:23 AM EDT
It is an issue of the antenna, nothing more I'm convinced.

At 146.000 my watt meter shows 49 watts out, and less than 1 watt reflected, at 147.69, I show 49 watts out, 5 watts reflected.

On 440 I get the same issue. The damn thing just isn't resonant.
Link Posted: 3/12/2006 6:57:13 AM EDT
Looks like you can test faster than I can edit a post

Which antenna is it? I've got an old MAXRAD dualband NMO that been working great for about 10 years. I've also got a larson that works very well.
Link Posted: 3/12/2006 7:06:45 AM EDT
I can highly recommend this antenna. The Austin Metropolitan. It's low profile and works fantastic. You already are drilled for the proper size hole. I use it for all three bands, but plenty of folks use it for two or one band.



The Metropolitan is a Tri-band VHF mobile adaptation of the Suburban antenna that covers 144, 220 and 440 MHz with great performance on all three bands. The antenna operates as a quarter wave radiator on each band and as such, requires a ground plane for proper operation. No tuning is required, as the antenna simply screws onto a low profile (Motorola/NMO style) mount. Only 19 inches tall, the Metropolitan can be used with the Austin Triplexer for simultaneous three band operation with separate radios!

Austin antenna

$39.95 available at Lentini Communications Lentini
Link Posted: 3/12/2006 7:08:14 AM EDT
I see... then I think you're on the right track with the Comet antenna. The SBB-5 looks about like what you're after. Good luck!
Link Posted: 3/12/2006 7:27:01 AM EDT

Originally Posted By Derek45:
Looks like you can test faster than I can edit a post

Which antenna is it? I've got an old MAXRAD dualband NMO that been working great for about 10 years. I've also got a larson that works very well.



Off the top of my head I couldn't tell you which model it is, about 36 inches, a coil in the center of the load in stainless. A real hunk of crap.
Link Posted: 3/12/2006 7:30:13 AM EDT
[Last Edit: 3/12/2006 7:39:47 AM EDT by Derek45]
if you look into the bottom of the antenna, does it look ilke the center conductor is low enough to make contact with the center conductor of the mount?

Link Posted: 3/12/2006 8:29:47 AM EDT
Comet SBB7, hands down. I've had most of the Maxrads and the Comets in my company's anechoic chamber, as well as quite a few other antennas. The SBB7 is the clear winner. The SBB2 is a close second and even though it is half the size it almost matches the SBB7. You would do well with both. They are both available with NMO bases.

It's absolutely amazing how many great dummy loads there are out there that look like antennas

Don't always assume good VSWR is your friend. A dummy load has the best VSWR around. I'd rather have an antenna at 3:1 that was radiating 90% of the forward power that is left than an antenna at 1.1:1 that was radiating all your forward power as heat.

aa
Link Posted: 3/12/2006 9:04:08 PM EDT
Strip the antenna down if you can and make sure that all the contacting surfaces are bare metal and making good contact. My brother got an antenna based on the good luck I had been having with mine (name brand, don't remember which at this point)and his didn't work for fecal material. After tearing it down, turned out that one of the threaded connections not only wasn't screwed down enough to make contact but it had been painted and that didn't help either. A few minutes with some steel wool and screwing it back down all the way made all the difference.
Link Posted: 3/12/2006 9:27:44 PM EDT

Originally Posted By mr_camera_man:
I see... then I think you're on the right track with the Comet antenna. The SBB-5 looks about like what you're after. Good luck!



That SBB-5NMO is the antenna I put on my car about three years ago. I 'compromised' and used an L-bracket mount at the trunk seam, but it's been a great performer teamed with my Kenwood TM-V7A.

Jim
Link Posted: 3/12/2006 9:46:38 PM EDT
I experienced poor performance from the Maxrad dual band antenna when I tried one several years ago. Much better luck with the Larsen 2m/440 antenna. One can also use a Maxrad 5/8 wave 440 antenna as a shorter dual band 2m/440.

As was previously mentioned, check the antenna mounting, cable, connector, etc. A shorted coax connector makes even the best antenna perform very poorly indeed
Link Posted: 3/13/2006 3:07:23 PM EDT
Update:

Received my Diamond in the mail today. That is one solid performing antenna, awesome signal output, I'm getting into repeaters that I could only receive about 1/8th the signal, now I'm 20 over 9 on EVERY repeater I have programmed.
Link Posted: 3/13/2006 4:02:13 PM EDT
Someone should check out that first antenna and figure out why it was working as a dummy load.

Jim
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