K1TTT wrote
>
>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.
>
The story about "molten" CATV cable sounds like someone connected it to
the 115/230V AC mains.
>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.
>
Here you go... <http://www.ifwtech.co.uk/g3sek/in-prac/best-of.htm#0904>
To download the complete magazine article, click "April 2009".
I have used these bias tees for many years to feed AC/DC power for
remote antenna relays on along both receive and transmit feeders. The
same design covers Top Band to 6m and comfortably handles 1kW of RF.
73 from Ian GM3SEK
>-----Original Message-----
>From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
>David Robbins
>Sent: 15 January 2014 12:36
>To: felipeceglia2@gmail.com; towertalk@contesting.com
>Subject: Re: [TowerTalk] AC/DC injection on CATV hardline
>
>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@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
>help?
>
>73,
>
>Felipe Ceglia - PY1NB
>-----------------------------------------------------------------------
--------------
>PR1T team member /// Rio DX Group member /// Araucaria DX Group
>member
>http://dxwatch.com /// http://reversebeacon.net ///
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