WRTC928

As I said, I've seen houses wired with aluminum wire and secured with steel screws without any significant corrosion. Granted, they aren't exposed to the weather, but they carry a lot of current. I'm not saying it doesn't happen and I'm not going to start randomly screwing dissimilar bits of metal together, but if Comet uses stainless steel radials screwed into an aluminum base, they must not be too concerned.

That makes sense. If three radials can provide a ground plane, expanded metal should work as well or better.

My radials are on the way from Comet. I hung it from a tree and ran a few tests using my improvised "mystery metal" radials. I think I'm going to like this antenna. I had a lot of work to do to get my deck ready to support the mast, but I think I have it ready now. I can raise the antenna as soon as the radials get here. Well, when I also have someone to help me. I can raise it with a rope using a tree branch as a pully, but I need someone to guide it and secure the clamps while I hold it up.

But then I wouldn't get to watch my pitbull bite their leg off on my surveillance cameras.

The one in Oklahoma City appears unused, but I'm trying to breathe some life back into it. The problem is that people ignore it because nobody uses it, but if everyone ignores it, there will never be any activity on it. I do know a guy who said he and his wife use it to stay in touch when they go to the state fair in the fall, so I guess it isn't completely devoid of life. I throw out my call sign every time I'm within range but haven't gotten a response yet. However, Tulsa has four 1.25m repeaters which get quite a bit of use, and I travel there fairly often, so I want to have that capability.

Since it seems to have worked for you, I'll give it a try. It's the only antenna I have that has good readings on 2m, 70cm, GMRS, MURS, and 1.25m. It has good signal on 70cm, GMRS, and 2m; I've never keyed up on MURS since I had a pair of MURS radios about 12-15 years ago. It would be convenient if it worked on 1.25m, because my car has limited real estate for antennas. I could have one antenna that did it all. On the truck, I have 3 antenna mounts, so it's no problem to have one antenna for GMRS/2m/70cm and another one for 1.25m.

The only reason I don't run the 2x4 on my truck is that it doesn't like the very limited ground plane I get on the back of the bed. It works like a dream on the roof of my car, though. It's probably the most versatile multi-band antenna available. Mine even shows excellent SWRs in the 220 MHz band. A good SWR doesn't necessarily mean it will transmit well on that band -- the ability to transmit is dependent upon the electrical and physical characteristics of the radiating element -- but it does mean that if I try it, it's very unlikely to damage my radio. I likely will try it sometime just out of curiosity.

TBH, I'm not sure. It has that dull sheen like aluminum, but that could just be the finish. I don't have a magnet handy, but a lot of stainless steel isn't very magnetic anyway. I think the whole "dissimilar metals" things is a bit overblown anyway. Cars and motorcycles bolt aluminum to steel all the time. If it were a part that carries a current, it might be different, but I've seen lots of aluminum wire secured to an outlet with steel screws for decades without any issue, so maybe not even then.

I'll recheck it when I have the antenna stood up. I hung it a few feet off the ground for the initial test. I wanted to be sure there wasn't anything to address before I got it 40' in the air.

That's true, but the Comet radials are stainless steel, and so are my temporary substitutes. Comet apparently doesn't think the stainless steel/aluminum interface is a problem. It may be a slightly different composition of stainless steel, but I doubt it's enough to cause problems before Comet sends me some. Meanwhile, I'm doing some testing and trial runs. At any rate, Comet isn't kidding when they say "pre-tuned". SWR < 1.2:1 across the entire GMRS band.

Access is just a matter of tipping the mast up and securing it to a post with hose clamps. I just now emailed Comet about the radials. In the meantime, I'm going to stand it up and do some tests with the improvised radials. It will be easy enough to tip it back down and change them when the "correct" ones arrive.

The rods I got are also stainless steel. I'm going to email Comet, but I'll use what I have until the new ones arrive.

I'm of the opinion that on 2m/70cm, anything more than 50 watts is just wasted, with perhaps a few exceptions under very unusual circumstances.

There aren't any buildings in the way.

I thought it was probably just an oversight, but I figured I'd ask if this was normal. I found an easy solution and I don't want to wait on radials. I'll probably email them anyway so I have spares.

Yeah, I figured it was probably something like that. I found an easy work-around, so I guess it's okay.

I bought the antenna a couple of months ago and didn't open the package until yesterday. I was surprised to find there were no ground plane radials included. Is this normal, or did I just get unlucky? It wasn't too big a deal, because I bought some 10" pieces of all-thread which should work just fine. The thread size is M5-0.8, in case you're interested. It seems to me that the radials are something which should be included. Maybe mine just slipped through that part of the assembly line.

I usually set A to whatever I want to monitor and B to some frequency that's unlikely to be used. If you have dual watch turned off, at most you'll have an extraneous channel displayed in the B window, but the radio will ignore it.

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.

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.

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.

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.

In an effort to replicate "field conditions" I threw an Abbree tactical tape measure antenna into a tree in my yard about 15-20' up and connected it to the repeater with 40' of KMR400 coax. Unsurprisingly, the results were very terrain-dependent. To my S/SW, Red Hill blocks my signals pretty effectively and I get barely 1/2 mile. To my W/NW, where the hill only partially blocks me, I got a couple of miles. To the east, I was able to get 11 miles until I went down the far side of a ridge, and to the northeast I got 13. I wasn't able to test it to the southeast or due north because there are no convenient roads. Considering how little altitude I had, that's pretty good. If I were on top of Red Hill, I probably could get a good 15 miles in every direction. I plan to get a 25-30' push-up mast and a better antenna for my RV, which should give reasonably good range. If I can get a good location, it should allow us to make some pretty long trail rides and stay in contact.

Yeah, definitely best to not draw attention to yourself.

It did occur to me after reading some comments that because this is a NGP antenna in a NGP installation, perhaps the real difference is that the cable I changed to acts as a better counterpoise than the one I replaced. That could simply be a fluke, because I doubt either US or Chinese manufacturers give any significant thought to its characteristics as a counterpoise. Maybe they do, but I'd be a little surprised.