Diamond SG7900 "Super Gainer" antenna

[WRTC928]

I have trouble finding suitable antennas for my truck because the only ground plane is on the roof, and for a variety of reasons, that's not practical for me, so I was interested in the SG7900 because it was advertised as not requiring a ground plane. There are 3 NMO mounts on my truck -- one on a front bed rail mount at the passenger side front corner of the bed, and one in each rear stake pocket. The one at the front is too close to the cab for most antennas, so SWR and performance suck, with one exception. I have a 50" (IIRC) whip CB antenna that has SWR <2.0:1 across the entire band and really blasts out a signal. The two points in the back have essentially no ground plane, and although some antennas have acceptable SWRs on some bands, it's almost impossible to find one that can cover the usual 4 bands (2m, 70cm, GMRS, and MURS). At least one band will have high SWR, and usually it's the 2 meter band, which I use quite a bit. 

I tried the 7900 in the front position just to see, and sure enough, SWRs sucked, but I expected that. However, in either of the rear stake pocket mounts, SWRs were 1.4:1 on 2m, 1.2:1 on 70cm, and 1.2:1 on GMRS. In the MURS band, SWR crossed over 2.0:1 right at 154.6 MHz, which is the highest frequency in the group. That's totally acceptable, although I don't use MURS in my vehicles anyway because the radios don't go down to 2 watts. Still, in the event of an emergency, it's good to have options and I do have the MURS frequencies programmed in with tx turned off.

I have to say, I was impressed. My experience has been that a manufacturer's description of an antenna as working well without a ground plane is about 30% wishful thinking, but this one works exactly as advertised. It purportedly has 7.6 dB gain at 430 MHz, so it probably produces a fairly similar result on GMRS frequencies. I don't have any way to formally test output, but I can hit GMRS repeaters all over central Oklahoma with it from my driveway, including some I've never gotten with any other antenna. It outperforms any GMRS-specific NGP antenna I've tried, so if you're looking for a GMRS antenna that will perform well in a location with limited or no ground plane, it deserves a look. Then, when you decide to get an amateur license, you won't need a new antenna. 

EDITED TO ADD: Apparently this is not a non-ground plane antenna. It is described that way on the DX Engineering website and I just took their word for it. Regardless, it works perfectly in my application where a ground plane is practically non-existent. As such, I wouldn't recommend you try it unless you're comfortable with the idea that it may not work without a good ground plane and you'll be out $115.

[73blazer]

I have this antenna and found the NGP to be false advertising. Not sure why they're saying that. I have an all fiberglass body '73 K5 Blazer and mounted this behind the tailgate off the steel bumper, and SWR was 2.9:1 on HAM UHF, 3.1:1 on GMRS, 2.2 on VHF. Put a ground plane under it (cookie sheet) and SWR never got over 1.5 on any band. It's a great antenna,with a ground plane. I actually called Diamond on this very point because DX is the only place that says NGP, nobody else says that about this antenna, Diamond says it will work, but not recommended, your results may vary, check your SWR...all the expected responses. Basically, it wasn't designed by them as NGP.  If your SWR is good, then that's awesome for you! You may be getting some GP still off your steel bed where you have it mounted though.

[WRTC928]

1 hour ago, 73blazer said:

I have this antenna and found the NGP to be false advertising. Not sure why they're saying that. I have an all fiberglass body '73 K5 Blazer and mounted this behind the tailgate off the steel bumper, and SWR was 2.9:1 on HAM UHF, 3.1:1 on GMRS, 2.2 on VHF. Put a ground plane under it (cookie sheet) and SWR never got over 1.5 on any band. It's a great antenna,with a ground plane. I actually called Diamond on this very point because DX is the only place that says NGP, nobody else says that about this antenna, Diamond says it will work, but not recommended, your results may vary, check your SWR...all the expected responses. Basically, it wasn't designed by them as NGP.  If your SWR is good, then that's awesome for you! You may be getting some GP still off your steel bed where you have it mounted though.

Interesting. It worked great for me. As you say, maybe there is a little ground plane effect from the bed of the truck. I assumed DX knew what they were talking about. You know what they say about assuming. In any case, it works great for me.

[Socalgmrs]

Yea that’s a ground plane antenna.  Not going to RX or t nearly as good as it could if it had a ground plane. 

[WRTC928]

42 minutes ago, Socalgmrs said:

Yea that’s a ground plane antenna.  Not going to RX or t nearly as good as it could if it had a ground plane. 

It's working just fine for me. Evidently, I have enough ground plane despite being mounted on the bed rail. DX Engineering described it as a non-ground plane antenna, and I took them at their word. I guess I won't be so trusting of them in the future. A couple of ground plane antennas have worked pretty well in that location. The Comet 2x4 was great on 70cm and GMRS, but had an SWR of 2.0-2.25:1 on 2 meters. The Comet SBB224 has stratospheric SWRs on 2m, 1.25m, 70cm, and GMRS on the passenger side and all below 1.5 on the driver side. Same mount, same coax, same distance. IDK. RF energy does funny stuff. 

If it hadn't worked, I would have been pretty chapped at DXE for describing it as NGP.

[73blazer]

There is one eham.net article where one commenter mentions it functions well without a counterpoise/ground plane. DX is a very reputable place, mabey they got their info from somewhere, mabey it's just a plain 'ole mistake? Who knows, But it's working for your setup and that's great! I found this worked great on my RAM 2500 CC roof  (with a tri-mag mount) and SWR's with same radio are 1.1-1.3:1 depending on freq in that setup. So it does seem to me it functions much better with a ground plane.

[SteveShannon]

Although Diamond doesn’t specifically say no ground plane, they do declare that the antenna will work nearly anywhere on a vehicle:

[WRTC928]

46 minutes ago, SteveShannon said:

Although Diamond doesn’t specifically say no ground plane, they do declare that the antenna will work nearly anywhere on a vehicle:

Yep, they stop just short of saying it doesn't require a ground plane. As @73blazer commented, DX has a good reputation which is why I didn't question their statement. And as 73blazer also observed, it probably does better with a ground plane, but even NGP antennas do that. I might get more farz with a ground plane, but TBH, I doubt it. I think the topography is such that a more efficient antenna wouldn't give me more than I already have. I'm happy with the antenna; I just feel a bit silly recommending it as a NGP when it isn't. I added an edit in my original post.