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 RF Ammeter...tuning...SWR ??? 
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Post RF Ammeter...tuning...SWR ???
I,m playing with an RF ammeter which I have fitted between the TCVR and ATU.

I tune the ATU for a reasonable SWR match and the RF Ammeter reads,,,say 50 on its scale....

If I then retune the ATU I can increase the current reading to ,say, 70 but then the SWR will read maybe 2.0:1.

Is there a best option?....... higher current?......lower SWR??

What say??

Roger G0IUW


Thu Dec 17, 2015 1:17 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
What are the readings if you put the ammeter after the ATU, or close to the antenna?

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Thu Dec 17, 2015 2:23 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
That might require some thought....

Its an MFJ 834 which is co-ax connected....my antenna is 450ohm ladder

Roger G0IUW
G6RRL wrote:
What are the readings if you put the ammeter after the ATU, or close to the antenna?


Thu Dec 17, 2015 2:28 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
Roger, what are you trying to achieve?

Putting an ammeter on the input to the matching unit is meaningless if you are putting the current transformer around the centre of the coax. If you are putting around the outside of the coax and you are getting a reading that is very meaningful, that means you have got RF on the outside of the coax, something you don't want because is means there is RF on the outside of the coax.

putting an ammeter on the output on one leg of the feeder is also pretty meaningless on a balanced system, now putting two ammeters one in each each leg of the feeder has much more meaning because at least you'll be able to see if the current is the same in each leg, but that won't tell you if the phase is the same.

Putting an ammeter on an end fed antenna is very useful if you are adding radials and trying to get maximum current up the antenna.

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Thu Dec 17, 2015 3:39 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
G4LNA wrote:
Roger, what are you trying to achieve?

Putting an ammeter on the input to the matching unit is meaningless if you are putting the current transformer around the centre of the coax. If you are putting around the outside of the coax and you are getting a reading that is very meaningful, that means you have got RF on the outside of the coax, something you don't want because is means there is RF on the outside of the coax.

putting an ammeter on the output on one leg of the feeder is also pretty meaningless on a balanced system, now putting two ammeters one in each each leg of the feeder has much more meaning because at least you'll be able to see if the current is the same in each leg, but that won't tell you if the phase is the same.

Putting an ammeter on an end fed antenna is very useful if you are adding radials and trying to get maximum current up the antenna.


Basically, I aquired this MFJ as a non-worker....the sensing unit uses the centre core thru a torroid in similar fashion to some SWR bridges.
I was reading the MFJ blurb about higher RF current beingrather more important than SWR values, so I connected it as they suggest between TCVR and ATU.
Really just to see if there was any difference with the results aforementioned.

Curiosity really.....the chances of me ever finding two thermocoule RF ammeters these days are remote or I would put one in each leg as we did in the 1960s.

Roger G0IUW


Thu Dec 17, 2015 4:02 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
G0IUW wrote:

Basically, I aquired this MFJ as a non-worker....the sensing unit uses the centre core thru a torroid in similar fashion to some SWR bridges.
I was reading the MFJ blurb about higher RF current beingrather more important than SWR values, so I connected it as they suggest between TCVR and ATU.
Really just to see if there was any difference with the results aforementioned.

Curiosity really.....the chances of me ever finding two thermocoule RF ammeters these days are remote or I would put one in each leg as we did in the 1960s.

Roger G0IUW


Thermocoupled RF ammeters? Roger, you are showing your age :D I must admit, I've popped a couple in the past. Luckily these days things are much easier with modern materials.
http://vk6ysf.com/RF_Current_Meter.htm

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Thu Dec 17, 2015 4:29 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
Aint that the truth!!!

G4LNA wrote:
G0IUW wrote:

Basically, I aquired this MFJ as a non-worker....the sensing unit uses the centre core thru a torroid in similar fashion to some SWR bridges.
I was reading the MFJ blurb about higher RF current beingrather more important than SWR values, so I connected it as they suggest between TCVR and ATU.
Really just to see if there was any difference with the results aforementioned.

Curiosity really.....the chances of me ever finding two thermocoule RF ammeters these days are remote or I would put one in each leg as we did in the 1960s.

Roger G0IUW


Thermocoupled RF ammeters? Roger, you are showing your age :D I must admit, I've popped a couple in the past. Luckily these days things are much easier with modern materials.
http://vk6ysf.com/RF_Current_Meter.htm


Thu Dec 17, 2015 4:44 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
G0IUW wrote:
I,m playing with an RF ammeter which I have fitted between the TCVR and ATU.

I tune the ATU for a reasonable SWR match and the RF Ammeter reads,,,say 50 on its scale....

If I then retune the ATU I can increase the current reading to ,say, 70 but then the SWR will read maybe 2.0:1.

Is there a best option?....... higher current?......lower SWR??

What say??

Roger G0IUW

Only just spotted this topic, so apologies for the delay.

Your radio is designed to work into a 50 Ohm load, so you should adjust the tuner for lowest SWR50.

In your example it seems you have adjusted the tuner so that the radio sees a 25 Ohm load (SWR=2:1). For a given output power, that will increase the current by 40%.

Steve G3TXQ


Sat Jan 09, 2016 11:12 am
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
Thank you, Steve....
Point taken and noted.

Roger G0IUW

G3TXQ wrote:
G0IUW wrote:
I,m playing with an RF ammeter which I have fitted between the TCVR and ATU.

I tune the ATU for a reasonable SWR match and the RF Ammeter reads,,,say 50 on its scale....

If I then retune the ATU I can increase the current reading to ,say, 70 but then the SWR will read maybe 2.0:1.

Is there a best option?....... higher current?......lower SWR??

What say??

Roger G0IUW

Only just spotted this topic, so apologies for the delay.

Your radio is designed to work into a 50 Ohm load, so you should adjust the tuner for lowest SWR50.

In your example it seems you have adjusted the tuner so that the radio sees a 25 Ohm load (SWR=2:1). For a given output power, that will increase the current by 40%.

Steve G3TXQ


Sat Jan 09, 2016 12:30 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
hell roger.
If you wish to check the balance of the feeder a pair of ammeters showing equal current will not do it.
steve showed one method on here using one ferrite ring over both feeders and using his calculations.

There is another vk station who designed a balance checker with one meter and a switch which put the two readings out of faze. I built this unit out of interest as I also use 450 ohm ribbon. It worked very well but for the love of me I cannot remember his call sign.

I use the dutch (fri) atu which I built and wanted to test it against a T network/ ballan.

don gw3rvg


Mon Jan 11, 2016 3:26 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
Thank you, Don.

I will do some googling...

Roger G0IUW
sedge wrote:
hell roger.
If you wish to check the balance of the feeder a pair of ammeters showing equal current will not do it.
steve showed one method on here using one ferrite ring over both feeders and using his calculations.

There is another vk station who designed a balance checker with one meter and a switch which put the two readings out of faze. I built this unit out of interest as I also use 450 ohm ribbon. It worked very well but for the love of me I cannot remember his call sign.

I use the dutch (fri) atu which I built and wanted to test it against a T network/ ballan.

don gw3rvg


Mon Jan 11, 2016 4:29 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
sedge wrote:
There is another vk station who designed a balance checker with one meter and a switch which put the two readings out of faze. I built this unit out of interest as I also use 450 ohm ribbon. It worked very well but for the love of me I cannot remember his call sign.

http://users.tpg.com.au/ldbutler/Line_D ... _Meter.htm

Don't use his original circuit - it only shows the magnitude of the two currents.

Steve G3TXQ


Mon Jan 11, 2016 4:56 pm
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 RF Ammeter...tuning...SWR ??? 
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Post Re: RF Ammeter...tuning...SWR ???
Thanks for the link, Steve

Roger G0IUW
G3TXQ wrote:
sedge wrote:
There is another vk station who designed a balance checker with one meter and a switch which put the two readings out of faze. I built this unit out of interest as I also use 450 ohm ribbon. It worked very well but for the love of me I cannot remember his call sign.

http://users.tpg.com.au/ldbutler/Line_D ... _Meter.htm

Don't use his original circuit - it only shows the magnitude of the two currents.

Steve G3TXQ


Tue Jan 12, 2016 6:05 pm
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