swr question

[oldcb]

i've been using my 1/2 wave for my testing of other radios, right now i've got a pretty good reading of 1.2 from channel 1 through 40 on my cobra 139xlr, but i've noticed higher readings when switching to other radios, i just hooked up my cobra 29 and went from 1.2 on the 139xlr to 2.3 on the 29, all i did was move the cable about 8" from the back of the 139 up to the back of the 29, whats up?..........................oldcb.............BTW, thanks for all that have helped me along the way with my many questions, i am getting better at this cb phenomenon, for me it's a whole new field, but i love to learn

 

[krokus]

Moved the cable in what manor?

 

[BirkenVogt]

If using the radio's built in SWR meter, I have seen some wildly different results, such that I don't trust them at all. Use a regular SWR meter and I bet you will see no difference between radios, and you will get a more accurate reading of what the antenna's SWR actually is.

 

[oldcb]

Moved the cable in what manor?

removed from the back of the 139, and connected to the 29 sitting right on top of the 139...............oldcb

 

[oldcb]

If using the radio's built in SWR meter, I have seen some wildly different results, such that I don't trust them at all. Use a regular SWR meter and I bet you will see no difference between radios, and you will get a more accurate reading of what the antenna's SWR actually is.

kinda what i was thinking, as the 29 was a used radio when i got it, and can tell someone has been in it before.....................oldcb

 

[jim202]

i've been using my 1/2 wave for my testing of other radios, right now i've got a pretty good reading of 1.2 from channel 1 through 40 on my cobra 139xlr, but i've noticed higher readings when switching to other radios, i just hooked up my cobra 29 and went from 1.2 on the 139xlr to 2.3 on the 29, all i did was move the cable about 8" from the back of the 139 up to the back of the 29, whats up?..........................oldcb.............BTW, thanks for all that have helped me along the way with my many questions, i am getting better at this cb phenomenon, for me it's a whole new field, but i love to learn

The only way to compare the 2 radios is to use an external SWR meter. This way your not changing the way you are trying to measure the different radios.

The internal SWR measurement built into a radio can be anything from true to total BS. It is there just to keep people happy that they have a way of trying to get some sort of a reading, even though it can be as far from the truth as water and matches.

 

[prcguy]

If the grounding or counterpoise of the antennas are inadequate there will be RF current on the outside of the coax and it will radiate just like the antenna. In this case moving the coax around can change the match.

There are various ways to fix this and addressing the inadequate ground is best but placing a common mode RF choke on the coax at the right spot (usually about 1/4 wave from the antenna) will usually tame the hot coax. You can make a choke by running several turns of the coax through a large number 43 mix toroid core available from Amidon associates. Look for an FT-240-43 core for high power.
prcguy

 

[JayMojave]

Yeah what PRC Guy said: Good call.

You can add different lengths of coax with your external SWR meter and see if that changes any thing, it is does you may have a hot coax, or RF Energy running down the coax causing a erratic SWR reading.

What type of 1/2 wave antenna do you have. Ifs a dipole you will need a Balun between the coax and wires, this will convert the unbalance coax currents to balance currents, and choke off RF Energy coming down the coax. Many say you don't need a Balun, I always use them.

Jay in the Mojave