8 replies to this topic

[kidphc]

Marc had mentioned he believes the current commercially available antennas are too small. So that had brought up some questions. I had planned on getting a CB radio for the interstate road trips. More comms, more situation awareness, or at least I hope. Currently, FTM400 CAP/MARS being installed with a Larson 2/70SH dead center in the roof. Probably will switch it out for a 2/70B in the center. Maybe a second 2/70B installed 20" inches aft for a ID 5100a. Stock AM/FM antenna is mounted to passenger side fender by the windshield.

 

Yes, parking garages are a big want, so I will need a reasonably flexible or lashable antenna.

 

It was going to be a small cheap 5 watt cb radio with one of the following:

 

-108 whip and breedlove ball mount on the rear driver fender. 

--- This one is tough since the previous owner had damaged the rear fender and the gas fill port is on that side.

-108 whip on the rear bumper

---This one is tough since the whip will contact the body when it is lashed down.

-5" firestick or trucker whip with top loaded coil on the driver front fender.

--- Passenger fender has the am/fm radio

 

I know none of the mounting points even come close to a terrible ground plane. Any suggestions on radio, antennas, placement any thing else? Things you guys found on previous installs.

 

 

[Jones]

You will get best results with a quarter wave whip (approx 102 inch) mounted on the passenger's side of the car - either the rear fender, or the right-rear part of the bumper.  This will give you a slightly directional pattern toward the front left of the car, or "further down the road" as it were.  Placing the antenna on the driver's side of the car will put the signal off to the right, which is not the oncoming traffic area.

 

If you want a good omni-directional pattern, but with slightly reduced overall range, use a 5-foot tall base-loaded antenna in the center of the roof. A good choice might be the Wilson 1000RT-B roof mount. Do not go with a magnet mount.  If you drive a sedan, you might also consider a K40 Trunk-mount.

[Jones]

I forgot to mention that with a K40 or a Wilson, if you are going to need clearance for a parking situation, either of these can be quickly and easily removed from its base by hand, and tossed into the back seat.

[kidphc]

It's a 02 Suburban. The whip was the first choice. There are alot of trees lining the roads so I was thinking left side was better due to it being in the center of the road.

 

 I figured a 1/4 wave was better. How much degradation in signal is there with going with a trucker style antenna. What can I expect with a bumper mount vs rear fender mount?

 

Thanks for responding.

[marcspaz]

Okay... so, here is the dirt.  Most antenna makers use the wrong velocity factor when calculating antenna length.  They calculate it like a cable, which is totally wrong.  Most makers either make a 102" whip or they load it like a 102" whip (Wilson 1000, Wilson 5000, 4' Firestick, etc.)

 

The proper length for a 1/4 wave antenna is 114 inches.  A few companies (such as MFJ) make a 108" whip, which if used with 4" spring and a 1" tall heavy duty stud mount gets you to 113", which is still an inch too short.  It is really close, though.

 

Also, when you install an antenna, you need the antenna to be as high as possible.  The roof is preferred.  Keep in mind, the lower the antenna, the more the body of the vehicle is shielding / absorbing the radio signal.  If you have a van or SUV and you do a bumper mount, your antenna is worthless.

 

Antenna cable length is also critical.  Don't use small cable.  An 18' RG58 cable with 259 connectors will give you the best performance.

 

The best results I have acquired while stationary, is using a bracket at the top of the body tub, a Wilson heavy duty mount (stud), a Wilson 10" antenna extension (actually measures 12") and a 102" MFJ whip.  When my SWR is properly set, the total antenna length is 113.75" AND above the body of the vehicle.

 

I am using a Galaxy CB, which is the best in the industry as far as I can tell.  I am able to talk 25+ miles with 1.5 watts dead-key, 2.5 watts modulated RMS.  When skip is active, I can talk to Huston Texas.

 

 

Now, here is the problem.  The whip is terrible when your moving.  The wind blows the antenna on a serious arc.  Whatever is in front of you will be able to hear you very well and for a long distance because the antenna is bowed so the signal is directional.  However, no one behind you is going to hear you because on the back side the antenna is point to the ground, right behind your vehicle.

 

So, when you are on the move, the Firestick is your best bet for omni-directional comms.  So, when I am driving, I use the 4' Firestick because it has 102" of wire wrapped around it.  I take the Wilson heavy duty mount (stud), a Wilson 10" antenna extension (actually measures 12") and a 4' Firestick, and still talk about 18 to 20 miles.  When skip rolls in, I can still talk to Flyin' J's just south of Huston.

 

Just to let you know how good my setup is... completely stock, I get the same range out of it as 2 friends of mine using tuned CB's and a 450+ watt HF amps.

 

Also, the rubber cap on the Firestick throws the match off.  Just leave the cap off.

 

Don't fall for the marketing hype. 

[marcspaz]

I forgot to mention; don't trust your SWR meter when you take readings at the radio. All that tells you is the circuit is balanced, not how well your antenna is tuned.

This isn't an "I think" situation where I am applying theory and got lucky. I am using a $600 antenna analyzer to tune the antenna to a 1:1 match on 27.185 MHz. Just the mount and a straight 102" whip has a 2.8:1 match and a 108" antenna has a 2.1:1 match on the same frequency.

I verified my analyzer against another operator's analyzer... getting the same results. I have personally done the same setup on 3 other vehicles other than my own, with the same results.

[kidphc]

I don't plan on DX'ing, so a SSB and a perfect antenna setup won't matter much to me. I really was just expecting close to 3-7 miles at most. Directional to the front won't be so bad fo the intended purposes of just listening for road hazards and such.

 

I had considered a No ground plane install, on the front fender by the windshield with a Firestick. I just didn't know what to do with all the extra coax. The FTM400 and all the other crap will be in the center console. The power line is coming through the steering column cover grommet, and there are additional power lines across the firewall for the dual battery and isolator. There really isn't any space inside of the engine bay to loose roll the coax and tuck it away.

 

A bumper mount would shield about 4' of the antenna. A front fender mount, about 2' would be masked by the truck. A rear fender mount would be about 3.5'.

 

I was going to treat it as an HF install and start bonding the truck. Atleast, I would be prepared if I decided to go HF.

 

Might have to revisit this later. Especially, after the FTM 400 is in and I can start getting an idea of what my noise floor looks like.

[kb2ztx]

NMO27 on the roof is your best bet for your application. Its easy to remove and cap when not needed or in garages. Flexible and works really well. Heck 90% of the time on the interstate i run a VHF 1/4 wave on my CB for RX only. Works fine for 1-2 miles around me. If i need more range i throw the NMO27 on the mount. (run the vhf for car wash)

[kidphc]

NMO27 on the roof is your best bet for your application. Its easy to remove and cap when not needed or in garages. Flexible and works really well. Heck 90% of the time on the interstate i run a VHF 1/4 wave on my CB for RX only. Works fine for 1-2 miles around me. If i need more range i throw the NMO27 on the mount. (run the vhf for car wash)

 

Thanks that opens a different possibility of putting the second 2m antenna on the fender, if I even go that route. Then place the CB where the 2nd 2m was going to go.