2M Antenna Recommendations?

[MobTuff]

Interested in antenna and wiring suggestions for an old 74 Land Rover with a hard top. All aluminium so no ground plane afaik.

The CB aerial is positioned at the rear of the truck using a firestick NGP set up.

I would highly recommend a half wave antenna. No ground plane needed. I've had mine mounted to an aluminum rack at the rear of the vehicle and now have it mounted to a fender mount and it worked well at both locations.

The antenna I use is the Larsen 2/70. Dual band half wave antenna. It's about $70 but I think it's totally worth the price. Looks nice too

 

[4x4x4doors]

Basic question from a n00b: Several mentions and discussion of SWR. Would one use the SWR meter one uses to measure SWR for a CB setup and using the same methods (connect, calibrate, key the mic and measure)? And would the corrective actions be the same (check grounds, etc?)

 

[abruzzi]

Basically. Some SWR meters work without using your transmitter--i.e. disconnect coax from radio, attache to meter. Set frequency on meter, and test. You also need to make sure your meter covered the desired bands. A 2m SWR meter does you no good on CB antennas if it doesn't also do 11m.

Geof

 

[DaveInDenver]

You also need to make sure your meter covered the desired bands. A 2m SWR meter does you no good on CB antennas if it doesn't also do 11m.

This is an important statement. In general the SWR bridge used for CB will NOT work for 2m and 70cm. If it works at all, it would give you a reading but it won't be valid.

BTW, the tool you refer to is called an antenna analyzer. I personally have a MFJ-269, which is about as cheap as you'd want to go.

 

[rockwood]

How well would the Larsen type stand up to the abuse it will get from low hanging trees in the New England forests? Or is there a better choice.

 

[MobTuff]

How well would the Larsen type stand up to the abuse it will get from low hanging trees in the New England forests? Or is there a better choice.

The Larsen I have has been great. It's tagged quite a few trees and hasn't missed a beat. Next time I'm going through the forest I'll mount the GoPro on the truck with the antenna in view. The one thing I've seen people do is where the antenna makes a "curlycue" they've put shrink tubing to make sure that branches can't get stuck and pull on the antenna. Larsen also makes a varrient of the antenna that is chrome and doesn't have the curlyque (seen here).

 

[4RunAmok]

The larsen antennas tend to handle abuse better than the more rigid Comet and Diamond antennas. I have had two larsen antennas mounted on my NMO mounts, and they've been through hell together, sometimes even fencing with one another.

 

[lugueto]

I have a Larsen 5/8 that has had its fair share of limbs, parking lot ceilings and everything in between. After all the abuse you can barely see any wear on it. Still works great.

 

[vicali]

I've just finished installing my radio, joined the radio club net the other night and I wasn't coming in clear, Simplex was loud and clear across town.
So I arranged to borrow the club's analyzer, plugged in the MFJ-259B last night and my numbers are;

@145.92MHz;
R- 7,
X- 12,
SWR- 4.6.

@144.04MHz;
R- 6,
X- 0,
SWR- 4.7.

 

[xbox73]

How well would the Larsen type stand up to the abuse it will get from low hanging trees in the New England forests? Or is there a better choice.

If you get the Larsen NMO 2/70B, where the loading coil is in the base, then the whip can be replaced by itself relatively cheaply, if damaged.

The Larsen I have has been great. It's tagged quite a few trees and hasn't missed a beat. Next time I'm going through the forest I'll mount the GoPro on the truck with the antenna in view. The one thing I've seen people do is where the antenna makes a "curlycue" they've put shrink tubing to make sure that branches can't get stuck and pull on the antenna. Larsen also makes a varrient of the antenna that is chrome and doesn't have the curlyque (seen here).

The only snag point on the NMO 2/70B is the coiled section of the whip approximately half way up, but the above tip should help eliminate that as a problem. Good tip, I think I'll try that on one of my mine.

 

[xbox73]

I've just finished installing my radio, joined the radio club net the other night and I wasn't coming in clear, Simplex was loud and clear across town.
So I arranged to borrow the club's analyzer, plugged in the MFJ-259B last night and my numbers are;

@145.92MHz;
R- 7,
X- 12,
SWR- 4.6.

@144.04MHz;
R- 6,
X- 0,
SWR- 4.7.

You really want your SWR < 2, and ideally 1.5 and below across your desired frequency range. Check that all your radio, antenna and analyzer connections are all tight. If you have a friend with a ham antenna that will let you borrow it, test his on your mount & wiring (and vice versa, if you can), so you know whether it's the mount & wiring or the antenna. I'd probably suspect the wiring from the ham radio to the antenna mount, before suspecting the antenna myself, but of course any of the above could be the issue.

 

[1911]

When SWR is well-balanced across the desired band and still high, this can also indicate not enough ground plane, though you'd think the expanse of the hood ought to do it.

 

[vicali]

Thanks everyone,

I went out to check that the cable with my meter to make sure it wasn't shorted inside to out or that the connections were all secure.

Here is the mount;


NMO on truck by vicali,

The cable checked out fine, no shorts, continuity between the insides, continuity between the outside, and no leaks across.
Looking at the bottom of the coil didn't look right though;


image by vicali,

The contact was folded right up to the top and away from the NMO mount. I carefully pulled it back down and screwed the coil back on. Plugged in the analyzer and got this;


image by vicali,

Tried it on low and hit the closest repeater, dialed in the farthest repeater that I couldn't key at 50w and worked it fine at 5w..

Again, thanks for your help.

 

[xbox73]

Thanks everyone,

The contact was folded right up to the top and away from the NMO mount. I carefully pulled it back down and screwed the coil back on. Plugged in the analyzer and got this;

Tried it on low and hit the closest repeater, dialed in the farthest repeater that I couldn't key at 50w and worked it fine at 5w..

Again, thanks for your help.

Glad you got it figured out.

 

[SteveG]

....The contact was folded right up to the top and away from the NMO mount. I carefully pulled it back down and screwed the coil back on.

Years ago, a customer of mine that owns a communications company told me the antenna I had was junk to get a better one. I thought... whatever. It's a piece of wire that sits on the roof of my car... my "junk" is fine. Fast forward several years (and several antenna problems) and I finally got a "good" antenna. I have to say, the difference in quality is immediately noticeable. I had an antenna with a base like the one shown above and replaced it with this one: http://www.ruggedradios.com/index.php?main_page=product_info&cPath=182_183&products_id=418

Rather than the piece of spring steel in the cheap antenna, the Laird above has a spring loaded button (like the center terminal on a distributor cap). The cheap antenna is a piece of cake to thread on because the spring is very weak. The Laird actually has some resistance to it so you know you're getting good contact. I imagine I'll get many years of good service out of the Laird.