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Discussion Starter #1
Hijack for any ham thoughts that come up, but I have a couple of questions. I’m going with an antenna that is “less” dependent on a ground plane and will probably mount it in the rear. In height, I’ll at least mount it at the top of the tub. I understand that using a metal extension will have an influence on the tuning of the antenna.

If I extend the antenna with, let’s say pvc pipe or fiberglass road markers, will that change antenna tuning?
How much is gained by putting more antenna over the height of the hardtop?
 

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1) Search for a top loaded antenna. The coil is up high and the short whip above is tuned for SWR. Trouble is the coils for VHF seem to be big and heavy, quite unlike the CB version. Theory is that the signal rx/tx will be above the loading coil??
2) Buy a no ground plane antenna for somebody like PCI race radio.
3) Stick a quarter wave antenna on the roof with a homemade ground plane.
4) Mag mount with 5/8 whip stuck on the hood. Pretty darn good - maybe better than the above??
What I use for my VHF is a front fender mount. Excellent in one direction and less 180 deg due to body. Reason simple and cheap. Used with the standard tuned 5/8 mast.
In any event it probably does not matter what ever you choose. Just get a 80 watt or higher radio for best results.
 

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Discussion Starter #3

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At VHF and UHF frequencies there is no need to add capacitance or inductance to an antenna to achieve a 50 ohm resistive match unlike CB antennas. 1/4 wavelength at 145 Mhz is 20" and 1/4 wavelength at 27 Mhz (CB) is 109". For the short CB antennas, designers must add in inductance and capacitance so it will match the 50 ohm transmitter output.

That article I wrote specifies two antennas that need no counterpoise or ground plane to work effectively, all of the others need to sit on some metal -or- you could add three pieces of wire to the shield side of the coax that are about 20" long. One point to remember is ALL antennas (and I mean ALL) are some variation of the basic dipole. It might not be obvious but it is true.

A general rule of thumb is to keep any antenna in the clear as much as possible for a couple of reasons - one of which is a mass of metal near the radiating element could detune it (shift its point of resonance or match) and the other reason is you have a less than desirable radiation pattern. A vertical antenna like we are discussing should have an almost perfect omnidirectional radiation pattern - place it near a mass of metal and that ideal omni pattern is changed.
 

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Discussion Starter #5
I’ve learned a lot of things, but this subject is like an unfurnished area in my head. I’m liking it.

I think the answers to my questions about raising the antenna higher on the vehicle with pvc or fiberglass are...

Yes, I could raise it up. Height in mounting is your friend, but it’s not practical for what Jeeps do.
 

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Raising the VHF antenna (or CB for that matter) a couple of feet for reasons other than moving it away from a mass of metal (i.e., you want better performance and improved line-of-sight) wouldn't matter very much - it's really not worth the trouble. Now if you are talking about a directional (beam) antenna for 2 Meters (145Mhz), moving it from say 8 feet to 50 feet would make a huge difference. Here's a link if you want to read more about line of sight at VHF and higher frequencies.
 

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I have mine in front, on the A pillar. In the rear my dead coyote rack is just too much mass of metal. The A pillar mount is not ideal or optimal, as seen on an SWR meter, and it does suffer the directional issue, but it works just fine for my purposes. Using the same Larsen 2/70 antenna on an NMO mag mount in the middle of the hood gets excellent SWR though. And putting it up in the middle of my coyote rack works superbly. So on my remote travels I just keep a mag mount base buried in my hope to never need stuff.

But I did briefly consider pulling out one of the hood snubbers and just permanently mounting it in the middle of the hood :D.



- DAA
 

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Yes too close to the A. Mine is forward about 18" on the fender/hood crack and my SWR is not great due to the reflected signal relation to the A. Mid hood fixes that issue as will moving mine farther fwd.
You will get a similar result mounting in the tail light location, but not as bad as a near A location. In the back mid vehicle would be better.
Get an SWR that give fwd and reflected and you can see why the SWR is poor.

I have mine in front, on the A pillar. In the rear my dead coyote rack is just too much mass of metal. The A pillar mount is not ideal or optimal, as seen on an SWR meter, and it does suffer the directional issue, but it works just fine for my purposes. Using the same Larsen 2/70 antenna on an NMO mag mount in the middle of the hood gets excellent SWR though. And putting it up in the middle of my coyote rack works superbly. So on my remote travels I just keep a mag mount base buried in my hope to never need stuff.

But I did briefly consider pulling out one of the hood snubbers and just permanently mounting it in the middle of the hood :D.
- DAA
 

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I have an MFJ, don't recall the exact model, might be that same one. Got it from Gigaparts, not too expensive, seems to work just fine.

- DAA
 

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I have a 20 year old version of this MFJ-259 - probably the most popular SWR analyzer ever sold. 20 years old and works as good as new. Actually it provides much more info than just SWR - for example it can tell you if the antenna is too short or too long (you can quickly find the point of resonance for an antenna.)
 

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Yaesu makes a good product and one of the big three (Kenwood/Icom/Yaesu.) They sometimes fall short with their user interface (programming and using various features) but once you get used to it, no big deal. I think it's more of an issue if you are used to Kenwood or Icom menus and then try to run a Yaesu.
 

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The FT400 has the benefit of a large color touch screen. The I find the touch screen operation intuitive and the large characters easy on my old eyes.
 

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Discussion Starter #19
I tell you what. I had no idea my frame of reference with ham radio was so small even though I’ve always loved it. It had my attention when I called home from the middle of the desert in 1968. The APRS technology jaw dropped me. A couple of days ago, my scanner on a 2 meter frequency picked up a Brit. in Japan on the Win system. APRS was just a Technician test question to me a month ago.
 

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APRS was my primary motivation for getting a nice dual band mobile. Well, maybe more accurate to say it was my Wife's motivation for being in favor of the expenditure :D.

She has been worrying after me to get a sat phone or spot device forever. My boss even tried to pay for a sat phone for me for the better part of 20 years. I'd rather die of hot poo than be tethered to that kind of electro nanny nonsense. The Ham w/APRS made both me and the Wife happy. Win-win. Never mentioned it to the boss at work. Win-win-win.

- DAA
 
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