Hi Bill,
I know you already got an answer to this question, and I just couldn't
resist giving another more general answer.
Overall, I would say the answer is no. You really have to know more
about the radio and the power supply before you can determine how much
voltage drop is acceptable. I know that you posted your question on the
Ten-Tec reflector, but I am going to answer more generally than just for
Ten-Tec radios. You need to know the range of DC voltage that the radio
can operate within, and you need to know the current draw under various
conditions of the radio operation. You also need to know what the
voltage produced by the power supply is, or can be adjusted to. Then you
need to use ohms law to figure out what the voltage drop will be at the
various current draws the radio will have in various modes of operation,
for a given resistance of wire. Unfortunately not all radio
manufacturers provide all of that information.
Lets suppose you have a radio that can work between 11 VDC and 15 VDC.
Suppose it draws 20 Amperes during key down CW. You could use a 15 volt
power supply and long or skinny wires that have a total resistance of
0.2 ohms (that would be 0.1 ohm on each of the two wires), and still
keep the voltage within the range the radio can work in. This is sort of
an extreme example, and definitely not a recommendation, just a possibility.
Once upon a time when undersea cables were coaxial, and there were
amplifiers along the way, DC power was sent into the cable to power the
amplifiers. AC would have been more of a noise (hum) problem with the
communications circuits on the cable. Several hundred or even a couple
thousand volts DC were sent at the shore termination facility, in order
to provide 50 or 100 VDC to an amplifier out in the middle of the ocean.
You can have a lot of voltage drop if you engineer the system to work
that way. Just be sure when the current is low, and the I * R drop
lowest, the voltage delivered to the load is not to high, AND when the
current is the highest it is ever going to be and the I * R drop is the
highest it is going to be, the voltage at the load is still high enough.
DE N6KB
Is there a rule of thumb for maximum voltage drop through the primary DC power
lead.
73
BillHarris w7kxb
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