Checking SWR

[CBA179]

I have a couple questions about SWR readings. Any help is appreciated.
I have my meter hooked up as follows: radio output to amp input/amp output to meter input and meter antenna to antenna. Radio and amp are powered by battery, antenna mount is grounded to truck bed and frame, truck bed and cab have ground straps to frame. Radio is a Galaxy DX959, antenna is a Tram TBC-12 Bigcat, all coax is RG-8x. I had the same set up in a truck I sold. This is all the same equipment installed the same way in a new truck.. I was able to get a 1.1 Swr reading on the old truck at the Dosy meter with amp off. Just wondering if I should be concerned about the different Swr readings. Any help appreciated. Thanks

Readings with amp hooked up and power off.
Swr reading using radio meter CH 19 is 2.0
Swr reading at the Dosy meter is 1.5

Readings with amp hooked up and power to amp on
Swr reading using radio meter is 1.3
Swr reading at Dosy meter is 2.5

 

[Tallman]

The only way to tune your antenna properly is with a antenna analyzer. I will not tune an antenna with a amplifier in line. You are tuning to a frequency not a power level.
If your antenna is tuned at four watts it will be tuned at four thousand watts.
If your radio has been "Tuned" with coils spread, you messed up. Because you now have Harmonics that will always screw up your readings.
The Dosey meter is better than the radio swr meter.

 

[CBA179]

Thanks for the reply. I don't have an antenna analyzer and don't really want to buy one. Do you think it would be worth it to tune the antenna with the amp disconnected using my Dosy meter? If I get the swr down to near 1.1 and add the amp back in should I disregard the Dosy SWR reading with it hooked up between the amp and antenna..In the past it always reads higher with the amp turned on. The Dosy meter also measures watts so I like to have it connected. My only concern is possible damage to the radio if SWR is to high. The strange thing is that with the amp running the meter built into the radio shows an SWR of 1.2-1.3. and the high SWR warning light does not go on.

 

[CBA179]

I should have included above. When I checked SWR with amp in the setup, the power to the amp was not turned on. My understanding is that the SWR will go up with amp turned on. Please correct me if I am wrong. Thanks

 

[999]

I used a PDC600 meter to set SWR for 20 years before I got my analyzer and it worked just fine. As a matter of fact when I checked the antenna on my truck with the analyzer that I had set with my PDC , I was dead on the frequency where I set it 10 years earlier.
If you know how to use your equipment, you can make things work without spending a ton of money that you don't have. That being said, I'm glad I have the analyzer.

 

[Tallman]

Thanks for the reply. I don't have an antenna analyzer and don't really want to buy one. Do you think it would be worth it to tune the antenna with the amp disconnected using my Dosy meter? If I get the swr down to near 1.1 and add the amp back in should I disregard the Dosy SWR reading with it hooked up between the amp and antenna..In the past it always reads higher with the amp turned on. The Dosy meter also measures watts so I like to have it connected. My only concern is possible damage to the radio if SWR is to high. The strange thing is that with the amp running the meter built into the radio shows an SWR of 1.2-1.3. and the high SWR warning light does not go on.

Tune the antenna with the Dosey and no amp in the circuit. Once you got that done you are almost ready to go. When you put the amp in line you can check your input to the amp with the Dosey for the SWR. Do not freak out when you check between the antenna and the amp and see it up high, Harmonics are showing up.
Run two Low pass filters in your setup. One between radio and amp and one between amp and antenna. You should be good to go.

 

[CBA179]

Thanks, I will give it a try as you described. I believe that's what I did about 12 years ago on my old truck and never had to touch a thing. Just wasn't sure since its been a long time. Thanks again

 

[CBA179]

I did what was suggested the results I got are:
Radio connected to dosy meter to antenna no amp.
Ch 1-1.7
Ch 19- 1.65
Ch 40- 1.6
These readings are so close together that I don't think there is much room for tuning.

Radio meter readings
Ch 1-1.8
Ch 19-1.9
Ch 40- 2.1
Next I went from radio to amp to Dosy meter to antenna amp turned off readings at Dosy meter
Ch 1-1.7
Ch 19-1.65
Ch 40- 1.6
Radio meter readings thru amp no power
Ch 1-1.9
Ch 2-2.2
Ch 40- 2.5
When I run the amp
Radio meter swr is 1.3
Dosy swr is 2.5
Not sure where to go from here. The radio swr meter is giving me reading opposite of the Dosy .Are SWR low enough to run amp without damage to radio. Thanks

 

[Tallman]

I did what was suggested the results I got are:
Radio connected to dosy meter to antenna no amp.
Ch 1-1.7
Ch 19- 1.65
Ch 40- 1.6
These readings are so close together that I don't think there is much room for tuning.

Radio meter readings
Ch 1-1.8
Ch 19-1.9
Ch 40- 2.1
Next I went from radio to amp to Dosy meter to antenna amp turned off readings at Dosy meter
Ch 1-1.7
Ch 19-1.65
Ch 40- 1.6
Radio meter readings thru amp no power
Ch 1-1.9
Ch 2-2.2
Ch 40- 2.5
When I run the amp
Radio meter swr is 1.3
Dosy swr is 2.5
Not sure where to go from here. The radio swr meter is giving me reading opposite of the Dosy .Are SWR low enough to run amp without damage to radio. Thanks

Do you have low pass filters in place? The SWR you radio will see is what is being reflected back from just the input to the amp. If your swr is high going into the amp with power on the input of the amp needs tuning.

 

[undertaker]

I would not trust the swr meter on the radio...

 

[999]

I would adjust the antenna up 1/4" and see if that lowers the reading any.

 

[W4KVW]

The only way to tune your antenna properly is with a antenna analyzer. I will not tune an antenna with a amplifier in line. You are tuning to a frequency not a power level.
If your antenna is tuned at four watts it will be tuned at four thousand watts.
If your radio has been "Tuned" with coils spread, you messed up. Because you now have Harmonics that will always screw up your readings.
The Dosey meter is better than the radio swr meter.

It is better for SWR but an unreliable wattmeter on it's best day. When I get them from Estates I use them for Targets at the range so they are actually good for something. I use an MFJ 259B to tune my HF & VHF antennas no matter what any SWR meter says on any radio on any band.

SIX-SHOOTER

 

[Tallman]

I did what was suggested the results I got are:
Radio connected to dosy meter to antenna no amp.
Ch 1-1.7
Ch 19- 1.65
Ch 40- 1.6
These readings are so close together that I don't think there is much room for tuning.

Those readings actually indicate the antenna is too long! move it down 1/8" at a time and tune on channel 20.

 

[CBA179]

Thanks for the replies. I will look into getting a low pass filter . Tomorrow I will try to move the antenna whip up a little. I will go by what the Dosy meter reads. I will try with amp out of the set up and with it in since it seems the same both ways. The crazy thing is the radio, and amp are the same that I had in my old truck. The coax is new and I replaced the antenna the other day since the old one was a Super penetrator that I thought may be the problem. Went thru a new whip trying to tune it but could not get the SWR as low as on my old truck 1.2 thru the amp when off and with the amp out of the setup. New truck has aluminum body (Ford F-150} but everything is well grounded. Thanks again Have a good weekend.

 

[999]

Those readings actually indicate the antenna is too long! move it down 1/8" at a time and tune on channel 20.

If the SWR is lower on 1 than 40 the antenna needs to go down (shorter). If the SWR is lower on 40 than 1 the antenna needs to go up (longer).