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measure of power OR how to do it right?

T

Turbine Divinity

Member
Sep 16, 2010
11
0
11
SO I just did another mosfet mod to a friends CB. (by the way , if you are buying the 520's get the VISHAY ones from Digikey. I got a couple from international rectifier and they really sucked) .

So when I test, I test with a 50 ohm dummy load and my Galaxy 717 SWR meterand am seeing a hair over 40w PEP. I confirm this on my Polaris meter then hook it to my firestick, confirm my SWR 1.2 -1 and talk to people clearly 10 miles away. everything is fine an dandy.

I hand the radio off to my buddy and he hooks it to his antenna (wilson 1000 base loaded on the top of his truck. dead center roof) I make a couple small adjustments and get his SWR downl that the needle barely moves on the meter. As close to 1 -1 as I have ever gotten. Flip to WATTS aaaannnnd

6 watts DK and 12 watts swing. HUH? Whaaaa? I go round and round with this trying to figure out what the hell is going on. I am thinking internal short on the antenna (base loaded coil) so I grab another K40 base loaded and lo and behold

5w DK and 10w swing.

Am I just doing something STUPID or am I missing something that any good CB tech should know.

Put the Dummy load on the end of his cable, 40w swing.

I admit I do not know everything, so any hints?
 

Turbine Divinity said:
SO I just did another mosfet mod to a friends CB. (by the way , if you are buying the 520's get the VISHAY ones from Digikey. I got a couple from international rectifier and they really sucked) .

So when I test, I test with a 50 ohm dummy load and my Galaxy 717 SWR meterand am seeing a hair over 40w PEP. I confirm this on my Polaris meter then hook it to my firestick, confirm my SWR 1.2 -1 and talk to people clearly 10 miles away. everything is fine an dandy.

I hand the radio off to my buddy and he hooks it to his antenna (wilson 1000 base loaded on the top of his truck. dead center roof) I make a couple small adjustments and get his SWR downl that the needle barely moves on the meter. As close to 1 -1 as I have ever gotten. Flip to WATTS aaaannnnd

6 watts DK and 12 watts swing. HUH? Whaaaa? I go round and round with this trying to figure out what the hell is going on. I am thinking internal short on the antenna (base loaded coil) so I grab another K40 base loaded and lo and behold

5w DK and 10w swing.

Am I just doing something STUPID or am I missing something that any good CB tech should know.

Put the Dummy load on the end of his cable, 40w swing.

I admit I do not know everything, so any hints?
Click to expand...

its amazing the differences you can see from a reactive load to a non reactive load.
 
linearone said:
its amazing the differences you can see from a reactive load to a non reactive load.
Click to expand...

Never seen that difference between my bird 82A and any tuned antenna.

birddummyload007.jpg
 
Look at the antenna with an antenna analyzer (MFJ-259B or something similar). Low SWR is one thing; a non-reactive load is another. It's possible to have a 50 ohm load that's highly reactive.
 
Dummy load vs Antenna

So here is the dummy load I have been using

Falcon Professional Ham CB Dry Dummy Load 150 Watts Max - #1 Falcon Antenna

And I have one I made myself with 2, 100ohm Non inductive 25w resistors and a paint can.

Same result across now 3 mag mount antennas.

Now I mounted a top loaded wire wrap (firestick) to his truck. aaaannnnd

10 w DK and 30watt PEP

Something is funky in magmount town ... I am just trying to wrap my head around it now.

They mystery continues.
 
Turbine Divinity said:
So here is the dummy load I have been using

Falcon Professional Ham CB Dry Dummy Load 150 Watts Max - #1 Falcon Antenna

And I have one I made myself with 2, 100ohm Non inductive 25w resistors and a paint can.

Same result across now 3 mag mount antennas.

Now I mounted a top loaded wire wrap (firestick) to his truck. aaaannnnd

10 w DK and 30watt PEP

Something is funky in magmount town ... I am just trying to wrap my head around it now.

They mystery continues.
Click to expand...

The trouble with accuracy your having as others have said is reactance,as all the antennas are 1/4 wave or loaded 1/4 wave antennas their typical radiation resistance is around 36 ohms,which at best would give you a 1.4:1 swr,as you have a 1:1 swr it tells you reactance must be making it so,if you used an antenna analyser you would see that reactance.

that is why an non inductive resistance is used as a dummy load,otherwise inductive reactance would mess with the readings.
 
Interesting

Just so I know what you are saying

So all things being equal, People should always use a dummy load to measure their power output vs using an antenna. There are just too many variables with an antenna to be accurate.

I don't have 299.00 for an antenna tester. While I enjoy making changes to radios for friends. It is not a business for me, It is just a hobby to see what I can do on the cheap with the tools I have. So far so good however, I am getting good at the Mosfet + Tune up on the 29's now that I have the tools to do it.

Thanks for the help however. You don't learn if you don't ask.
 
Turbine Divinity said:
Just so I know what you are saying

So all things being equal, People should always use a dummy load to measure their power output vs using an antenna. There are just too many variables with an antenna to be accurate.

I don't have 299.00 for an antenna tester. While I enjoy making changes to radios for friends. It is not a business for me, It is just a hobby to see what I can do on the cheap with the tools I have. So far so good however, I am getting good at the Mosfet + Tune up on the 29's now that I have the tools to do it.

Thanks for the help however. You don't learn if you don't ask.
Click to expand...

Basically if you want accuracy,or at least near accuracy allowing for innacuracy of nearly all power meters,the bird included,the best way is on a dummy load

A better way might be to use an oscilloscope instead,but thats a whole other story.
 

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