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.

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.

The stiffness of RG8 is specifically why RG8X was invented. It would be extremely difficult, if not impossible, to route LMR400 in most of the ways required in a vehicle.

Exactly. So, what's the point of telling me I'm using the "wrong" coax? I'm sure ladder line would give better results, but it won't fit through the holes in the floor of the back of the cab, to say nothing of going under the side bed rail, over the top of the front bed rail, down the front of the bed, under the cab, and back up through the hole in the floor. 15' is about as short as I can go and it has to be very flexible. I'm not aware of anything "better", but I'm open to suggestions.

I'll be civil to him when he stops being an ass.

That's nice to know, but LMR400 and Heliax aren't practical for vehicle installations.

I'll look at that for next time. In the meantime, I'm not having any more line loss than 99% of the installations out there. Less than most, in fact.

No, you illiterate. I specifically stated that it's an NGP antenna. But even an NGP antenna can often benefit from a good ground plane.

Every mag mount antenna and every NMO kit I've ever seen uses RG58. I'll bet all of you have at least one on one or more of your radios. RG58 is even more lossy than RG8X, so I'm mystified about why your installation is right and mine is wrong. If the dummy load isn't between your ears, tell me something I can use. Be Elmer, not Mr Magoo.

So what is the right cable? "You're doing it wrong" isn't helpful information. It might make you feel superior, but it sure as hell isn't going to save me any heartache or money.

It sounds like you're saying there's no point in testing. Any cable that's practical for a vehicle application will be lossy. RG58 is even worse, and that's what pretty much all mag mounts and NMO kits include. Are you suggesting we should use LMR400 for vehicle antennas? Why do you assume the antenna has an SWR of 10:1?

Alright, smart guy. How do you hook up an antenna without using a cable?

It is certainly interesting when you chart it that way. As you say, the SWR improved on the bands for which the antenna was not designed, but not on the bands for which it was designed. In effect, it made this antenna a little more broad-banded. Now I need to do some more testing. I'll try a couple of different antennas and maybe the dummy load test.

I was surprised. On the forums, there's always someone saying how Chinese coax is crap, real men only by USA cable, etc., but nobody's ever shown me the actual results. This is only one specific set of circumstances, and it's possible that if I had a good ground plane under the antenna, or a different antenna, the difference wouldn't be so obvious. Maybe in some cases, there's not enough difference to make a difference (RIP Paul Harrell), but in this case, it was worth the extra expense.

IME, the general rule is that assuming both antennas are appropriate to the band I want to use, I'll get a bit more distance and clarity both rx and tx with the longer antenna. Often it isn't enough to matter, buy sometimes it's pretty noticeable. Individual radios may sometimes prefer one antenna over another for reasons I don't understand. That's kind of a long way around to say try them both under the same conditions and see what you get.

I recently installed some NMO mounting points on my truck, but for a variety of reasons, I wasn't entirely satisfied with them and decided to do it over. For the first installation, I used generic Chinese RG8X coax, but this time I went with USA-made MPD digital RG8X. The first thing I noticed was that the MPD coax is much more flexible and easier to work with, but even more significant is what happened to my SWRs/Smith graphs. With the Chinese coax feeding a Diamond SG7900 Super Gainer NGP 2m/70cm dual-band antenna, the 2 meter and 70 centimeter bands were good, GMRS was in the "I can tolerate it if I don't use it too often" range and MURS (Which I've never used and could live without, but why not test it?) Started at 2.0:1 and went up from there. The first four pics are the sweeps of GMRS, 2m, 70cm, and MURS in that order with the Chinese coax and the last four are the same after changing to the MPD coax on the same antenna. 2m and 70cm remained good and even improved a little, but GMRS and MURS improved dramatically -- all the way to, "Yeah, that'll do." If (like me) you have sometimes wondered, "Does it really make that much difference?" the answer is yes, it does. The MPD ain't cheap at $2.34/foot, but I only needed 30 feet. TBH, even if I needed 100 ft, I'd buy the MPD. The difference is that obvious. As the saying goes, if you buy the best, you only cry once.

I don't know why it's so hard to teach people to do that. It drives me nuts. I tell them, "Push the button, THEN talk. Think of it like the second or so it takes your phone to dial a number. You're essentially doing the same thing." They smile and nod, then continue to start blowing from their pie-hole before they push the button.

Giving it to GMRS doesn't really solve anything except the question of what to do with it, but it doesn't really make sense to create a new class of license for that band. I suspect that if it were given to GMRS, users would divide up into "VHF GMRS" and "UHF GMRS" folks depending upon their needs or whims. And, of course, the occasional oddball would "need" to have two radios just because. Yes, repeaters would be expensive to build and maintain, but 6m AM simplex would be great for some things, especially with 50-100 watts. A lot of folks who now need a repeater to talk to the spouse unit from office to home could probably just go to 6m simplex. Farms and ranches that now use repeaters might be able to get rid of them. The easiest solution for the FCC would be to set some basic rules, toss it into the GMRS category, and say, "You figure it out. Or don't. Whatever."

Me too, and it works just fine.

That's awesome!

What radio are you using? If I understand correctly, you're in Death Valley or somewhere around there? Your geography is more favorable to radio waves than what most of us have. I can't get a hundred miles here even with my 63" antenna and 50 watt radio. But for my normal shopping trips, the little UT-72 works just fine.

Really, my point was that an antenna that does what you want is a "good" antenna. I see a lot of comments about how the UT-72 and UT-72G aren't very good antennas or even are "crap" because other antennas can be heard much further. That may be true -- I haven't tested it -- but the 72 and 72G have served perfectly well for what I've done. If I can't get the signal out with a UT-72, I can't get it out with any other 1/4 wave antenna either. Obviously, if I were offroad rather than in an urban/semi-rural setting, my results might be different. Today I was able to get a response from someone on a GMRS repeater 59 air miles away in my truck, but that antenna is 63" tall. You never get something for nothing.

I stand corrected. You are right.