This is because watt meters don't really read watts at all. It's simply an RF volt meter that has been calibrated to read in watts based on the assumption it's always operating into a 50 ohm load. Increase the load impedance and the RF voltage goes up. Unfortunately this leads to misunderstanding because the watt meter shows more power even though much less power is being transferred into the load. With a 100 ohm load, your 50 ohm watt meter will incorrectly report twice the power output. On the other hand it will also indicate a 2:1 VSWR. The only accurate part is the 2:1 VSWR. Wattage can only be measured into a 50 ohm load.
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Antenna Tuners....Yea or Nay?
- Thread starter Eastside
- Start date
This is because watt meters don't really read watts at all. It's simply an RF volt meter that has been calibrated to read in watts based on the assumption it's always operating into a 50 ohm load. Increase the load impedance and the RF voltage goes up. Unfortunately this leads to misunderstanding because the watt meter shows more power even though much less power is being transferred into the load. With a 100 ohm load, your 50 ohm watt meter will incorrectly report twice the power output. On the other hand it will also indicate a 2:1 VSWR. The only accurate part is the 2:1 VSWR. Wattage can only be measured into a 50 ohm load.
I tried to tell him the same thing earlier in the thread but apparently it didn't sink in or was ignored.
http://www.worldwidedx.com/meters-m...2123-antenna-tuners-yea-nay-4.html#post319075
The meter is reporting forward power correctly. Look at it in terms of what the feedline must be able to pass. 2:1 SWR means somewhere along that line there will be twice the voltage and current encountered with a flat match. The reflected power is not all lost. In some cases most of it does get radiated and in doing so winds the watt meter tighter.
If someone wants a meter to only read power delivered to a load it must be terminated with its design impedance. Bird recommends use of a dummy load if their meter is to be used for this purpose. RTM.
If someone wants a meter to only read power delivered to a load it must be terminated with its design impedance. Bird recommends use of a dummy load if their meter is to be used for this purpose. RTM.
Yes any mismatch is abuse and all those dirty variables might just make this all go away :laugh:
what do you want me to do?, i have an old dentron supertuner, a homebrew tuner, a bird 43, tellewave44, lp-100, resistors or dummyloads and a high quality infrared thermometer,
if im understanding the debate correctly, i think i can get virtually all of the transmitters 50ohm output into a 200ohm or worse load resistor with very little loss so long as i use a low loss line to the load and the tuner is sized for the task,
imho the bird will report what you claim, i have not tested the idea myself but folk smarter than me have.
if im understanding the debate correctly, i think i can get virtually all of the transmitters 50ohm output into a 200ohm or worse load resistor with very little loss so long as i use a low loss line to the load and the tuner is sized for the task,
imho the bird will report what you claim, i have not tested the idea myself but folk smarter than me have.
Hey CK sorry for taking so long to reply, between family and so much work piled up in the shop I have had little time to do anything.
OK I buy the watt meter theory of needing a 50 ohm load to display a calibrated reading as most seem to be designed to work into a 50 ohm load.
I used two Autek WM1 computing meters, they have circuitry in them to compute the load and the power per say.
So question, how about using an O'scope, same set up, 10 w carrier, connect scope to sample the RF before the tuner and and then connect it after the tuner say into a 3:1 VSWR, would that result in an accurate test as the O'scope does not need a 50 ohm load ?
OK I buy the watt meter theory of needing a 50 ohm load to display a calibrated reading as most seem to be designed to work into a 50 ohm load.
I used two Autek WM1 computing meters, they have circuitry in them to compute the load and the power per say.
So question, how about using an O'scope, same set up, 10 w carrier, connect scope to sample the RF before the tuner and and then connect it after the tuner say into a 3:1 VSWR, would that result in an accurate test as the O'scope does not need a 50 ohm load ?
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i did a quick test, not sure if its what you wanted, others may want to do their own test,
first i set a cb radio to 3w fwd power on my bird43 using a 5w slug into a dc-2ghz dummyload, reversing the slug shows zero reflected power,
next i added a second wideband load in parallel with the first load using adaptors and inserted a homebrew atu between loads and bird43 using a short jumper then adjusted the atu for zero reflected power into the 25ohm load, reversing the slug bird43 reads 3w fwd power,
next i adjusted the atu for a reading of 4w fwd power, reversing the slug bird43 reads 1w reflected power.
first i set a cb radio to 3w fwd power on my bird43 using a 5w slug into a dc-2ghz dummyload, reversing the slug shows zero reflected power,
next i added a second wideband load in parallel with the first load using adaptors and inserted a homebrew atu between loads and bird43 using a short jumper then adjusted the atu for zero reflected power into the 25ohm load, reversing the slug bird43 reads 3w fwd power,
next i adjusted the atu for a reading of 4w fwd power, reversing the slug bird43 reads 1w reflected power.
The last test addresses the situation in question. Thanks.
Bird 43 adds reflected power to forward power reading.
Next.
If it 'adds' the forward and reflected power by it's self, why make the thing so that you have to turn the 'slug' to read the reflected power. Your statement just doesn't make sense. YOU have to do the adding to get total power output (the combination of both forward and reflected power).
- 'Doc
- 'Doc
If you consider what actually happens to reflected power it makes perfect sense.
Try reading Reflections by W2DU. It might make sense then.
Bird recommends using an absorption wattmeter for accurate foward power measurement. Did you catch that in the manual you just read?
If that were true, wouldn't it add forward power to reflected power as well? IOW, wouldn't both slug positions read the same?
EDIT__
NVM, your talking about re-reflect, not reflect
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Google Baluns as well then take that idea and what the other's are explaining and it will make it a bit more clear. The Library near you might have the ARRL's guide to antenna's and it is fantastic for explaining all of this. Each ARRL Handbook cover's it too but their Antenna guide is a must read if you want to truly understand and maybe even start making or modifying your own antenna's.
You can also take an antenna tuner and basically use it to match a solid state transistorized driver or radio to a very primitive tube amp in place of a properly designed input tuner. Their used to be a Field Manual for Improvised Wire Antena's for Army Ranger's too that was very good at making complex things seem stupid simple!!!Sometimes just wrapping your mind around an idea is the hard part after that it can handle more complex idea's along that same line with ease it is making that first big leap that is the hard part! That is why I am tossing out different sources. Hope it helps.
That was a lifetime ago and in a far away land griped by strife and we did not have a presence their on the ground at all......LOL
You can also take an antenna tuner and basically use it to match a solid state transistorized driver or radio to a very primitive tube amp in place of a properly designed input tuner. Their used to be a Field Manual for Improvised Wire Antena's for Army Ranger's too that was very good at making complex things seem stupid simple!!!Sometimes just wrapping your mind around an idea is the hard part after that it can handle more complex idea's along that same line with ease it is making that first big leap that is the hard part! That is why I am tossing out different sources. Hope it helps.
That was a lifetime ago and in a far away land griped by strife and we did not have a presence their on the ground at all......LOL