Yes, you can put lots of power over the coax... however, dc and pwm variable
speed control are not equivalent. If it were a real dc motor I would say
that yes you could filter the motor noise with no problem. But when driving
it with pwm you will also have to fight the switching noise of the power
supply. While it may be possible it will be harder than just filtering dc
to switch a relay or power an lna.
David Robbins K1TTT
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: Kipton Moravec [mailto:email@example.com]
> Sent: Saturday, October 23, 2010 23:12
> To: firstname.lastname@example.org
> Subject: [TowerTalk] Power Over Coax
> I am aware that people use coax for DC power to power electronics.
> I have a 12V 1A (max) motor. It will be variable speed by using PWM
> (Pulse Width Modulation)
> I have an engineer that says I can power the motor over the coax. He
> says no problem -- people power over coax all the time. I do not believe
> him. I can believe it can work for low power stuff, like the LNA for my
> GPS antenna. But a LNA does not generate the same level of noise a motor
> My concern is that a motor is electrically very noisy. Sparks occur as
> the brushes cross the rotor. This coupled with the inductance of a 1A
> motor and a long cable can produce some serious noise.
> I do not think one can filter it (within a 4 square inches of board
> space) to the point that I would be willing to hook up an HF receiver
> and see if it blows out the front end.
> I thought I would ask the collective wisdom of the TowerTalk people.
> Do you folks think powering this motor over the same coax your HF radio
> is on is doable?
> Kipton Moravec AE5IB .- . ..... .. -...
> "Always do right; this will gratify some people and astonish the rest."
> --Mark Twain
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