Antenna idiot (me!) seeks enlightenment

[kanabecsys]

Well, here goes...

I guess I ought to admit it: I'm an idiot when it comes to installing antennas. Even though I try to use good quality components and do it right, I still have a horrible time getting out.

Latest case in point: the rig in my car. I installed a 110w VHF MCS2K in the trunk and a Motorola quarterwave NMO on the trunklid. Very simple install. Should have worked like a charm. But yet, the furthest distance I've been able to transmit was around 15 miles in semi-wooded terrain. I know the radio is fine, and the antenna was brand-new in the bag.

Can anybody recommend a good reference which would teach me some theory, give some examples, and show me what I'm missing?



Keith

[EOppegaard]

What type of cable are you using to run between the antenna mount and the radio?

There are tons of websites out there you could find on antenna theory, I would do a search on Google and see what you could dig up.

[Rick Rock]

First off, if you're looking for reliable long distance, lose the 1/4 wave and get an antenna with @ least 3db gain. /\/\ has a rather nice VHF gain antenna NMO mount that I have had nothing but good luck with. Also, when assembling your antenna onto the NMO mount, be sure to lube the NMO with electrolytic grease (bulb grease, available @ any auto parts store). /\/\ sells the above antenna for around $50-55, but there are some on ebay for less than 1/2, and I have personally purchased 1 from him and they are OEM new antennas. Here is one of his auctions if you're interested: http://cgi.ebay.com/MOTOROLA-POLICE-EME ... dZViewItem

[This is not my auction, but just being used for a visual example of what I am talking about.]

Rick

[nmfire10]

15 miles on simplex with a 1/4 wave? This is bad?

[Tom in D.C.]

You didn't state that you did any system checking when you installed the items.

1. Did you check the match between the transmitter and the antenna?
2. Did you check that the antenna is radiating at all?
3. Did you check the feedline for shorts or opens, including the antenna itself
when it's mounted on the vehicle?
4. Did you cut or otherwise adjust the antenna itself for the center frequency
that you're using?
5. There's also a remote chance that the length of the feedline is resonant,
which is bad news but easily remedied.

A quarter-wave antenna has a low angle of radiation, which is bad news if
you're way out in the woods. A 3db gain antenna has a higher radiation angle
and is better. The quarter-wave works great in the city but out in the boonies
you want a gain antenna.

[kb0nly]

15 miles on a puny 1/4 wave out in the boonies isn't bad. For real performance go with a 3db gain antenna as others have mentioned, a 5/8 wave antenna.

Yeah, it's taller, and it will probably whack some trees in the boonies, but a good flexible antenna and the worst that happens is a nice "twang" as it hits stuff.

[va3wxm]

A quarter-wave antenna has a low angle of radiation, which is bad news if you're way out in the woods. A 3db gain antenna has a higher radiation angle and is better. The quarter-wave works great in the city but out in the boonies
you want a gain antenna.

I think you mean the other way around, Tom.

15 miles on 1/4 wave isn't bad considering it's a less-than-optimum spot on the car (trunklid). And I'd be a little leery about radiating 110 watts only a few feet from my head.

Lots of good suggestions here.

[wa2zdy]

You also didn't say what was at the other end.

On simplex to another similarly equipped mobile, I'd call 15 miles darn good. That was about all I ever got with 135w and a 5/8 on the trunk. On the roof the signal would have been better. And at the other end in the case I'm thinking of was a GM300 and another 5/8, that one on the trunk lid.

However, there were some repeaters I could get into full quieting from 70 miles away. And a base station depending on height of the antenna would be good for 30. A guy standing around with an HT would hear me maybe 5 miles away.

So you see, the whole thing is variable. It really doesn't matter how much power you run once you get past line of sight. Assuming you weren't trying a tall repeater, it sounds like your setup is working about right.

Good luck.

[kanabecsys]

Okay, glad to hear that my experience is about normal - I thought sure I was doing something radically wrong, what with the wattage and all.

I did inspect the system to make sure everything was okay - all cabling was good, the ends were all fine, etc. I don't have an SWR meter or any other such equipment, so a visual check is about all I can do. Also, the cable I used is just the RG58 that came with the antenna.

As for the other end, I've transmitted to a similarly equipped mobile, and to an HT which was around 20' above ground level (setting in a window, facing towards the transmitter). There are no repeaters locally which I can test with.

The antenna is mounted as such that a few inches of it extend over the roof of the car, so I suppose that's helping a little in the directional-ness department. The antenna is cut for around 151, and I was keying on a channel in the mid-154's (I intended to cut the antenna somewhere in the middle of the highest and lowest freqs I planned to transmit on).

I am considering moving up to an antenna with more gain, but I haven't decided what level of hamsexiness I want to take my car to yet

Thanks for the help!


Keith

[kb0nly]

If you had your had your ham license there is a fair selection of repeaters in the area.

On VHF, within 25 miles of Mora..

Milaca 145.3500 - WB0MPE o 141.3
Isle 146.6100 - WB0SYO oL(FOREST LAKE)
Rush City 145.3300 - N0ABR oa
Cambridge 146.6400 - WR0P oae 146.2
Foreston 146.7450 - N0GOI o
Princeton 145.4700 - KG0UY o 114.8
Princeton 146.8950 - N0RPP oe 203.5

There is a couple UHF up in the area to..

Cambridge 443.9750 + WR0P oae 114.8
Foreston 443.6750 + N0GOI o 114.8

Just a quick search using Mora as the center and a 25 mile radius. I know i can hit a couple of them from Highway 23 when passing through.

[kanabecsys]

I don't have my ticket, although I do plan to get it in the near future. I used to have access to a commercial repeater, but it is now off the air. So it's all simplex for me.

FWIW I may have an opportunity to build my own repeater soon, but until then I'm stuck talking simplex.


Keith