Sudden SWR spike

By brick I meant the wall type between the radio/antenna, should've been more clear I suppose. The magnet has been stuck to the metal since first mount.[/QUOTE]


It is possible that there is a bad solder joint in the radio, it does happen.

 

After reading your original post, I thought I would reply on your question. Technically the SWR (standing wave ratio) isn't in the radio. Now the radio does have an industry standard impedance of 50 ohms. So that's why it's best to use 50 ohms coax. There are guys who use the 75 ohm tv cable which works with a little more tuning of the antenna, but it's better to just use the 50 ohm coax. Okay, by using an external SWR meter, while adjusting the antenna for the best match (lower SWR reading), you are basically eliminating the RF power that the antenna is sending back to the radio. I usually give people a real simple example by saying that with a high SWR reading, like over 2.1, the antenna is acting like a mirror that reflects your image back, instead of radiating the signal into the air, which isn't good. Just a simple visual to help them understand.
Now with a good matched antenna system, the majority of the RF power from the radio is radiating out into the airwaves, which is what you want. That is accomplished by having a good RF ground (commonly referred as ground plane) which is electrically the second half of the antenna. That's why it's so important to have metal preferably under a mobile antenna. Hopes this makes sense.

 

Take it off of the brick and slap it straight onto the A/C unit. The SWR will improve a bit. A magnet mount antenna needs to be on metal.[/QUOTE]

From time to time I've seen people post about putting an antenna on a outside A/C unit. My first thoughts are that it won't work. Since I don't know what amount of metal needed for a decent match with a CB radio and a mag mount antenna, I decided to check it out since I had the time. I did this experiment with my rig expert 55A antenna analyzer and a K40 with tunable tip and 4 inch magnet. Sorry for the reflections but the sun is really bright today.


Hopefully you can see an SWR reading of 1.9 with the antenna on the corner of A/C.
Got an SWR of 2.2 with antenna on the motor. I actually expected a higher reading. The extra picture shows a sweep of the CB band, and surprisingly it shows an SWR of 1.5 on the 10 meter band around 28.145 megahertz. Of course the return loss is very poor, which is to be expected. With the antenna mounted about 4 feet off the ground, maybe you could talk half a mile?


An

 

Just an FYI, a magnet mount antenna uses the vehicle for additional capacitance in order to achieve the needed system balance. A car in itself is part of the system, it allows the balance to be created.

Using it with a grounded item doesn't allow the system to be completed.

 

That's an excellent point about the electrical ground on the A/C unit, combined with a capacitance type antenna.

 

I know it is, I spent time paying homage to the great one and as required I had to sacrifice a Spark-o-matic over the altar of the CB gods and asked them if the great one can impart some wisdom into my head about magnet mounts.

 

Ooh nooo.....not the spark-o-matic...lol.
Okay that confirms it, GGALLIN1776 I'm standing by my first bit of advice I gave you. Ditch the magnet antenna... Ha.

 

No, I just gave you a link to Amazon for a small Tram 1499 CB base antenna. Nothing mentioned about coax length. The Saturn b100 looks like the exact same antenna, except they mention coax length of 18 feet or longer. You wouldn't want to roll up several feet of coax. A dipole antenna would work, but it needs to be vertical, instead of horizontal.