[TowerTalk] AC/DC injection on CATV hardline

David Robbins k1ttt at verizon.net
Wed Jan 15 07:36:27 EST 2014

50/60hz or dc shouldn't matter.  the only way to get molten cables is by too much current, you can do that with either ac or dc, but you need some kind of high current source to do it.

There are commercial injectors available, but the old heathkit remote switch box used nothing more than a 100mh coil to connect the ac or half wave dc to the coax and a .1uf cap to block it from the tx and antenna.  you do have to be sure that the capacitor will handle the max voltage AND current at the highest frequency, so don't just pick any old audio cap out of the junk box, get a good ceramic or tx rated cap.

Jan 14, 2014 07:28:16 PM, felipeceglia2 at gmail.com wrote:

Hello folks,

I need to inject AC or DC into a run of CATV hardline (.860)

I've been told by a CATV technician that it isnt a good idea to inject DC
into it, he couldn't explain why. He mentioned seeing molten cables when
someone tried to do it.

I got a pair of AC injection boxes, but when measured on the VNA each of
them presents more than 35dB insertion loss on 1.5MHz...

Do you guys have any expertise on this issue? If AC is really needed, any
particular diagram? 60hz seems to be fairly close to 1.5MHz to isolate it
using a single capacitor as done with DC. Maybe a highpass filter should


Felipe Ceglia - PY1NB
PR1T team member /// Rio DX Group member /// Araucaria DX Group member
http://dxwatch.com /// http://reversebeacon.net /// http://riodxgroup.com

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