same problem, swr`s

[dxing440]

:bdh: I know some of you are getting tired of my ignorance,BUT,
I have moved the antenna up, (open coil roadtech) above the cab and ran extra grounds to the base of the bracket and the plate at the top, where the antenna is attached to. And another ground to the amp. GROUNDING I dont think is the problem.
JUST by moving the antenna up, i was able to lower the swr`s to 1.2 on ch1, 1.1 on ch 20, and 1.1 on ch 40
TURN the dx500 ON, and swr`s are at 3.1 at ch 1,20,and40
TURN the dx500 OFF, swr`s back to 1.1-1.2
More ideas please!

 

[Beetle]

What sort of meter are you using to read SWR and where is it located - between radio and amplifier, or after the amplifier?

 

[dxing440]

tc4001 is the meter, and right after the amp.

 

[Marconi]

tc4001 is the meter, and right after the amp.

What does the meter do with the amp out of the line?

If the meter is a Dosy and not a Dosey Test Center, then check the coax connectors on the back where the center pin goes into the meter. That metal is very thin and with use I find they tend to bend open some, and then they might not make a good contact to the pin in your coax connector. Dosy uses junk connectors IMO.

 

[dxing440]

with the amp OUT of line, and the meter where the amp should be, its 1.1 all 40ch,
with the amp OUT of line, and the meter right behind the radio, its 1.1 all 40ch,
with the amp IN line and TURNED OFF, the meter right behind the amp, its 1.1 all 40 ch,
with the amp In line and TURNED ON, the meter right behind the amp, its OVER 3.1
Im thinkin its in the amp itsself, ive got a wilson 5000 mag mount coming, Ill try it.
If swrs are still high with amp, its probably in the amp,Right?

 

[Marconi]

Yep, I rectum sore.

 

[russ]

I have a TS 400v with a Radio shack external meter all tied to a roof mount Wilson 5000..As well, with a 2950dx my swr's with out amp on are fine but, as soon as I turn the amp on my swr's swing high..but, as I turn the variable just slightly on the Amp the swr meter instantly goes way down..I have also tried my galaxy 959dx with the same set up and my SWR with amp on and variable all the way up my swr stays low...So, some radios work differently or match up in some way better...not sure why but, maybe some one who has a better reasoning/understanding as to why this might happen with different radio's with amp and a wilson 1000 or 5000.

I own multiple antennas but, seem to only have this problem with my Roof mount Wilsons....my last investment was in a Sirio 5000, mounted on same roof mount as my Wilson 5000, and has worked flawelessly with any radio with same amp...SWR's stay way down either amp on or off...

 

[roadrage]

Where are you when you are testing? If there are any objects near you, your system may be "seeing" them with the amp on. Your system would still have a reactance to it, it just might not be noticable with the amp off. Overhead powerlines, trees, houses, etc. can cause negative readings on you meter. i have seen many things affect SWR. In my driveway I can watch my SWR meter go up from 1.2 up to 2.0 by driving forward 6 feet toward the garage. I left the allen wrench in the set screw on the mast and it threw my reading off too. Whenever I have a problem, I always start with the simple and easy first. If something doesn't power on, I check if its plugged in. If the car sputters, I look at the gas guage. Often times it is the simple things we overlook. Not that it is always an easy fix, its just a good place to start.

Also, what kind of coaxial cable are you using, and how old is it?

 

[W5LZ]

The simple answer is that the output impedance of the amplifier is not the same as that of the radio (which we assume is 50 ohms). It's a very common problem with 'no tune' circuits, they just aren't 'close' enough.
Are there other possible reasons for that happening? Sure, but with the information given, the amplifier seems to be the culprit. Try it into a dummy load, see what happens.
- 'Doc

 

[Beetle]

Either what 'Doc said, or the amplifier is tending to be a non-linear device, putting out power on lots of frequencies where it's not supposed to. It might be fun to look at this with a spectrum analyzer and see how much of his signal is on channels 1, 20 and 40, and how much is spewing out in the form of spurs, harmonics and such.

 

[roadrage]

The simple answer is that the output impedance of the amplifier is not the same as that of the radio (which we assume is 50 ohms). It's a very common problem with 'no tune' circuits, they just aren't 'close' enough.
Are there other possible reasons for that happening? Sure, but with the information given, the amplifier seems to be the culprit. Try it into a dummy load, see what happens.
- 'Doc

If that is the case, shouldn't he be able to put a tuner between the radio and amp.

 

[KM3F]

When the amplifier is keyed up, the input is switched to the amplifier input circuit.
The input circuit is not even a close match to 50 ohms.
What would need to be done to correct this mismatch is unknown until some one who understands matching gets a look at it to determine what to do.
It may be as simple as finding the right length cable from the radio to the amplifier if the amplifier input circuit has no problem.
Good luck.

 

[The Mad Scientist]

i went through this very same problem and i may be able to help.

i see that you didn't mention what kind of radio that you are using with this setup?

the first thing i would look at is the correct alignment of the tx chain for the band/frequencys that you are using. i have found that most of the time this alignment is not right. and the set of filters right before the fist mixer will cause excessive harmonics if not aligned propperly which the amplifier will just make worse.

the second thing i would look at the the two 10 uh chokes in that texas star, as most do not know that they have been replaced with a chakes of the same value but a thicker wire winding on it that does not have a large voltage drop like the origional, and seems to do a better job of keeping the harmonics out of the bias network. by applying these solutions brought my swr down considerably.

i have also noticed that for some reason that the wilson antennas, especially the newer bargan made verity's are more senisitive to harminics. i would agree as mentioned earlier that going to the sirio 5000 series antennas would also help.

hope this helps.