[MRCA] M and S net - being more careful

[Al Klase]

Hello Eugene,

I've got to believe it's protected against stuff like that, it's a field 
radio for Pete sake.  The Harris RF3200 has a similar scheme, but I 
can't find the schematic for the tuner interface option.  What I do know 
is that, modern (going back 30 years) three-terminal voltage regulators 
are short-circuit protected.  The output current "folds back" to a safe 
level.  Look for one in the circuit.

73,
Al

On 2/25/2012 8:58 PM, W2HX wrote:
> A coupla weeks ago I checked into the M&S Net with my newly acquired racal
> BCC-39B. I have an antenna over the house so I decided to bypass the built
> in ATU which has only a whip attachment and limits output to 25W.  By
> passing would allow me to run 50W and have a bnc connector.  Despite my OCF
> dipole having a terrible match on 60m and with an SWR of 3:1 I was able to
> get a signal out and had some nice sig reports.
>
> Talking to another owner of this radio, I remembered that this radio puts
> out 24VDC on the antenna BNC connector. This is used to power the ATU and by
> sending PWM on that 24V antenna BNC connector, it can send band information
> to the ATU (very clever). This allows the ATU to be situated 50 meters away
> from the radio itself if necessary using only an RF cable and no other
> control cable.
>
> At some point a few days after my check into the net, it struck me that my
> OCF dipole has a balun within it, and might present a DC short to the
> feedline.  Well, it does (confirmed by the mfg of the antenna). So I started
> getting a worried that a) I might have damaged something in the radio by
> presenting a short or b) damaged the balun putting 24VDC across it for about
> 1 hour (the power is applied in Rx and Tx).   A regular dipole without any
> dc path between the segments would of course, be fine.
>
> I am still doing the circuit analysis to see what could have actually
> happened, but suffice it to say, I need to be more thoughtful when
> connecting seemingly innocuous radio system components. And a reminder to
> other folks as well. Think twice, connect once! I'll report back if anything
> actually did get damaged (btw: I am pretty sure the radio wont be damaged
> but I'll have to double check).
>
>
> 73 Eugene W2HX
>
>
>
>
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/