RF reading problems

[Stump31]

Does anybody have an idea why I would get different RF power reading from two different antennas on my mobile? One antenna is a LiL WiL when I key up the dead key shows 3.5-4watts and the swing will be 15watts just like it should. When I hook up my Wilson 2000 mounted on the roof rack the dead key will show 15 watts with little or no swing. The SWR on both antennas are in the 2.5 range and I am working on getting them down. I just would like to know why I am getting such High dead key on the Wilson 2000. I use the 2000 on another vehicle and it works fine. I am using 213 superflex coax with the 2000 to the SWR meter. The radio is a Cobra 148GTL.
Thanks ,

Stump31

 

[Moleculo]

Lil Wil is a magmount and is achieving a proper ground plane. The Wilson 2000 on the roof rack is not achieving proper ground plane because either the roof rack is non-conductive, or it's mounted to the roof in a way that is not conducting to the roof. Your SWR reading on the Wilson 2000 is wrong. Whenever you see unusually high power readings after you change antennas, the SWR is way out of whack.

 

[Captain Kilowatt]

It would be interesting to see what the actual impedance and reactances were on each antenna. One may be showing inductive reactance and the other capacitive reactance. I know some broadcast transmitters will operate into an antenna with inductive reactance but not antennas showing capacitive reactance despite both antennas showing the same very low SWR. Maybe the finals are picky or the meter is responding to the different reactances in a different manner.

 

[Stump31]

QRN, which is the Wilson 2000 showing reactance or capacitive reactance? The funny thing is within a five mile raduis everyone says the signal from both antennas sounds fine. I know something is wrong by looking at the meter. I will try a magnet mount for the Wilson 2000 and see what type of reading I get. The mount for the roof rack was grounded to the hatchback of the car but I guess it was not good enough. Thanks for both of your replies. If anyone else has anything to add please don't hesitate to post something.

Regards,

Stump31
PS: I forgot to mention I tried hooking up an AT-KW1 no ground plane antenna matcher but all I got was a buzzing sound when I keyed the mike with the 2000 hooked up.

 

[W5LZ]

I think your problem has two parts to it. One deals with reactances present in the antenna (resonance) and the other deals with impedance matching. Both affect each other, but they are not the same things at all. They have to be treated separately, sort of.
The reactance and resonant part plays a big part in how efficient you antenna is, how well it radiates. There are combinations or reactance and resistance (impedance) that can make a watt meter read both high or low. Reactances do not contribute to producing power, they don't 'radiate' worth a hoot. But if those reactances are of the right kind and value, they can certainly make it seem like they do. And they can also turn that power back from that antenna, it never gets radiated. It's more likely to have two identical antennas behaving differently than two of any kind of antenna behaving exactly alike, in the same situation.
What do you do about it? Try re-tuning them. And while it may be the accepted, or easy way to do that, an SWR meter is terrible for tuning antennas, it just doesn't tell you what you need to know directly. It can tell you quite a bit indirectly, but that means you have to know what you're doing and how to understand those indications. Unfortunately, most people don't.
- 'Doc

(Do I know it all? Why, yes, from the day I was born. That's why that @#$ doctor spanked me! I told him how to fix his antennas.)

 

[mackmobile43]

I think your problem has two parts to it. One deals with reactances present in the antenna (resonance) and the other deals with impedance matching. Both affect each other, but they are not the same things at all. They have to be treated separately, sort of.
The reactance and resonant part plays a big part in how efficient you antenna is, how well it radiates. There are combinations or reactance and resistance (impedance) that can make a watt meter read both high or low. Reactances do not contribute to producing power, they don't 'radiate' worth a hoot. But if those reactances are of the right kind and value, they can certainly make it seem like they do. And they can also turn that power back from that antenna, it never gets radiated. It's more likely to have two identical antennas behaving differently than two of any kind of antenna behaving exactly alike, in the same situation.
What do you do about it? Try re-tuning them. And while it may be the accepted, or easy way to do that, an SWR meter is terrible for tuning antennas, it just doesn't tell you what you need to know directly. It can tell you quite a bit indirectly, but that means you have to know what you're doing and how to understand those indications. Unfortunately, most people don't.
- 'Doc

(Do I know it all? Why, yes, from the day I was born. That's why that @#$ doctor spanked me! I told him how to fix his antennas.)

My dad always said that you are the smartest man there is and what you didn't know probably wasn't worth knowing.

 

[W5LZ]

Ha! Got him fooled don't I??

 

[Moleculo]

The mount for the roof rack was grounded to the hatchback of the car but I guess it was not good enough.

How did you do this? Did you use good wide ground strap or did you just run a little wire?

 

[Stump31]

Well problem solved folks. I switched radios and put the wilson 2000 on a magnetic mount and things are good. The SWR is down to 1:1 and the RF acts as it should, dead key 4watts and swings to 25watts. I guess the finals on the Cobra 148GTL were picky for that type of install just like QRM said. The Galaxy 99v works just great. By the way Moleculo the ground wire was a 8ga fine strand wire. I did not check running the radio to the roof rack again since the magnet mount worked so well.

Thanks for all the replies .


Stump31