I play with uhf and am cb radios. been asking around the forums about tuning the antenna on my 27mhz unit. It receives well I can listen to truckies in aussie and picked one up in honolulu. I cant seem to get my swr under 3. Its a base loaded stainless whip mounted on steel shed roof. earth connections are good any ideas?

The metal roof being your "ground plain" raise or lower the antenna above the roof. And/or shorten the coax until desired SWR is reached. If the antenna is adjustable, do that too.

Grounded (earth)? Which? The roof or the antenna? if the antenna is grounded to earth remove it and try again.

Use to put coat hangers (antennas) on the top of Douglas fur trees and never grounded the antenna.

The timing of this is amusing, I haven't really thought about CB Radios for many years... but about a month ago I started looking into them again. Alot of Jeep Safaris still use them, and I've thought about getting one.

I'm surprised they are still as expensive as they are, considering how cheap some of the shorter band radios now are (Baeofeng for example, supports an incredible range of frequencies, for both send / receive ... all for $25).

Anywho... somewhere, I have an old late 70s / early 80s Cobra CB... somewhere.

-DallanC

Ive tried shortening the antenna. Doing that got the swr on channel 1 and 40 close to the same reading but didnt lower it. At the moment it sits at just under 3 but from what ive read you should try and get it down to around 1.5. I might try a different antenna

1.5 or lower. Now I have to find my notes of 20 years ago. I shall get back to you later.

These are a weird set midland 203. On my meter its transmitting just under 4w. Opened it up and for some reason its got an aa battery inside it. Its got an am fm switch on it. Still trying to figure out exactly what that does..as far as i know fm doesnt go as low as 27mhz

Aah...Found it.

Base and Mobile Antenna Adjustments:

1. If the SWR is high on channel #1, the antenna or coax is too short.

2. If the SWR is high on channel 23 or 40 (old and new radio), the antenna or coax is too long.

3. Check both the first and last channel and compare. Make the adjustment to the coax or the antenna. Which ever is most convenient.

4. When adjustments are completed, check mid channel to insure that the curve is not too high.

5. Optimum SWR is 1.5:1 or lower. 1:1 being the best.

These are my notes from yester year.

I have a Cobra 29 with added crystals and a Uniden Washington with side band. Coat hanger is Wilson 5/8 wave.

Many years ago...back in the day when men were men and pansies were flowers...I used to play with 27mhz, but my setup was a little "different" to the average setup. I was running a 110w linear amplifier and I built myself a full wave 2 element Quad antenna and had it 1 wave length off the ground. I didn't earth it separately and it worked a treat. Using a power mic, i would "broadband" and over modulate about 2 thousand miles away. I had to wait until around 2am before turning it on because it would "blow out" tv's within a 500m radius. The set I was using had an adjustable SWR dial on it, so I could adjust the SWR as needed. Those were the days.

Sometimes I would head for the coast and park close to the water, and had a length of wire with a heavy fishing sinker on the end. I would clip this to an Earth on the car then throw the sinker end into the water...was a pretty good ground plane and stretched my distances. I also had a mate who used to do similar at home, only he attached a wire to the 1.5m high cyclone wire fence that ran around his boundary. The fence was maybe 50m long in total and this became his ground plane.

The only time I've had to physically adjust the SWR of an antenna was on my mobile, and that was to simply and carefully nip the top off the antenna (wound fibreglass) until the desired SWR was achieved. It might be worth doing some research and seeing if you can purchase an antenna base with a built in automatic adjuster. My shooting buddy plays with HF (he's an ex Army signaller) and purchase one of these for his HF setup. He also has about 4 diffferent types of antenna (sloping wire, V etc)...all home made.
Have a look at this website for a cheap easily constructed base antenna with around 1.5:1 SWR...

www.instructables.com/...n-antenna/

These days, I have a 40 channel UHF mobile radio and an older 27mhz SSB set, both running about 5w. I must plug in my 27mhz unit again to see who's out there these days. I've been told best chance is around November, but who knows.

Ok cool. My antenna can be adjusted by loosening a grub screw to lengthen and shorten it in the base. It started out at about 5.5 and ive got it down to 3 on chanel 1 and 40 shortening it doesnt get it any lower

so the aa battery seems to be for the memory in the unit' never seen that before. With natural disasters etc happening I think cb radio is a good idea as far as comms goes. cell phone will be useless when the network goes down..

northdude wrote:

so the aa battery seems to be for the memory in the unit' never seen that before. With natural disasters etc happening I think cb radio is a good idea as far as comms goes. cell phone will be useless when the network goes down..

There's a solution for that... Peer to Peer wifi networking. You can make smaller networks of cell phones without cellular providers as long as there are wifi routers within range of each other.

"Open garden" was a test of this a while back. Problem is people need the app software before the apocalypse, not after.

But... its very possible to establish smaller networks of cell phones without a cell service provider. It would work across a city where there is a higher density of wifi routers.

-DallanC

ok we are a bit rural so that wont work..

If the power is out won't the routers be down too?