[GreenKeys] Loop supply options

[Ralph Mowery]

I always use something to fine tune it to 60 ma.  Much more and you may cook the magnets on the machines like the 15 printer.   Much less  and you lose some ability to correct for distortion on the signal.

 

Sometimes I use a power resistor that has a slider contact on it to set the current as they seem to be easier and less expensive than a rheostat.   I have used a power supply that I can adjust the voltage to fine tune the current.    For local loops the voltage is not too important as long as it is over 60 or 70 volts.  It does help to have a higher voltage of around 120 to 200 volts if using a demodulator to copy off the radio.   Even at that 10 or 15 volts is not going to make much difference.

 

I wish we could get by with about 25 volts as it is easy to use a 3 terminal regulator to set the loop for 60 ma and it would be constant no matter what the load is with in reason.

 

 

Ralph ku4pt

 

 

 

From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Paul Heller
Sent: Monday, September 09, 2019 12:16 PM
To: Ralph Irish
Cc: Jeff G; greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Loop supply options

 

Does anyone use a rheostat to fine tune the loop current, or is that a silly idea and close is good enough? 

 

Paul
W2TTY





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