How to calibrate an SWR Meter on a Dentron MT-3000A?
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Ham4CW
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I had a look around the web and found two versions of the MT3000A tuner, one which appears to be an old version, the other type is the one featured in the attached pdf manual.
If your tuner is the one in the manual then to calibrate the meters is a fairly quick process, but I did find MANY comments around the web to the effect that MT3000A meters were/are notoriously inaccurate, but whether this is true or not I am unable to say.
So, for the tuner in the manual:
1) Set the antenna selector to the "Coax 1 Direct" position.
2) Connect a dummy load to the Coax 1 socket, and a suitable transmitter to the RF-IN connector.
3) With the transmitter set on a mode that will give a continuous carrier i.e. CW AM FM and with sufficient power to give a full scale deflection on the forward power scale of 200 Watts*, adjust R4 to set the pointer to full scale deflection.
4) With the transmitter set on a mode that will give a continuous carrier i.e. CW AM FM and with sufficient power to give a full scale deflection on the forward power scale of 2000 Watts*, adjust R5 to set the pointer to full scale deflection.
* Note: if you cannot obtain enough power for a full scale deflection then you could go for a power level that will allow setting the meter to one of the mid scale calibrated markers say 100 Watts, 50 Watts etc, though full scale would be best if possible.
5) Reverse the transmitter and dummy load connections so that the dummy load is on the RF-IN connector, and the transmitter is on the Coax 1 connector.
6) With the transmitter set on a mode that will give a continuous carrier i.e. CW AM FM and with sufficient power to give a full scale deflection on the reflected power scale, adjust R6 to set the pointer to full scale deflection.
7) Your done!
In the method above when I say to use 'enough power' this means you should use 200 Watts for the 200 Watt range, and 2000 Watts for the 2000 Watt range, and whatever power level is marked for FSD on the reflected meter (I could not make out from any photos I could find what the power level was).
Also, you could always use a lower power level to start with just until you are sure all is ok with the meters and coupler, and also to safeguard yourself from 'pinging' the meters if the level controls (i.e. R4 R5 R6) have been adjusted too high.
The above method will work with the tuner shown in the attached manual, but other tuners/meters may need other adjustments (some couplers have a balancing capacitor and so on).
Regards, Mark.
If your tuner is the one in the manual then to calibrate the meters is a fairly quick process, but I did find MANY comments around the web to the effect that MT3000A meters were/are notoriously inaccurate, but whether this is true or not I am unable to say.
So, for the tuner in the manual:
1) Set the antenna selector to the "Coax 1 Direct" position.
2) Connect a dummy load to the Coax 1 socket, and a suitable transmitter to the RF-IN connector.
3) With the transmitter set on a mode that will give a continuous carrier i.e. CW AM FM and with sufficient power to give a full scale deflection on the forward power scale of 200 Watts*, adjust R4 to set the pointer to full scale deflection.
4) With the transmitter set on a mode that will give a continuous carrier i.e. CW AM FM and with sufficient power to give a full scale deflection on the forward power scale of 2000 Watts*, adjust R5 to set the pointer to full scale deflection.
* Note: if you cannot obtain enough power for a full scale deflection then you could go for a power level that will allow setting the meter to one of the mid scale calibrated markers say 100 Watts, 50 Watts etc, though full scale would be best if possible.
5) Reverse the transmitter and dummy load connections so that the dummy load is on the RF-IN connector, and the transmitter is on the Coax 1 connector.
6) With the transmitter set on a mode that will give a continuous carrier i.e. CW AM FM and with sufficient power to give a full scale deflection on the reflected power scale, adjust R6 to set the pointer to full scale deflection.
7) Your done!
In the method above when I say to use 'enough power' this means you should use 200 Watts for the 200 Watt range, and 2000 Watts for the 2000 Watt range, and whatever power level is marked for FSD on the reflected meter (I could not make out from any photos I could find what the power level was).
Also, you could always use a lower power level to start with just until you are sure all is ok with the meters and coupler, and also to safeguard yourself from 'pinging' the meters if the level controls (i.e. R4 R5 R6) have been adjusted too high.
The above method will work with the tuner shown in the attached manual, but other tuners/meters may need other adjustments (some couplers have a balancing capacitor and so on).
Regards, Mark.
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