[W2CRA] Ohms Opinion Exercise

[Tony Ploski]

Here is what I get:

nominal resistance of phone line = 120 ohms
replacement interface relay = 6000 ohm coil, 2 ma activation current, 
use a 12V relay.

still searching for such a relay

Tony
W2HWW



On 11/11/2013 1:02 PM, William Powell wrote:
> All,
>
> Measured control to transmitter phone line and thought it would be
> neat to drop it here as a practical exercise:
> At the control site there is a ~12V power supply that connects to the
> phone line via relay contacts.  When the transmit site interface sees
> voltage on the phone line it activated the transmitter.
> We need to replace the transmit site interface as it is not documented
> and made from "unobtanium" (Google it if you must).
> At the TRANSMITTER end I measure the following:
> Voltage across the phone with everything connected as normal:
> 	12.25V
> Voltage across the phone with everything DISconnected:
> 	12.39V
> Voltage across the phone with it terminated with a 100.5 Ohm resistor:
> 	5.66V
> Voltage across 100.5 Ohm resistor when placed in SERIES with the
> normal setup:
> 	0.20V
>
> What is the nominal resistance of the phone line?
> What are the parameters required of the replacement interface relay:
>   - Coil resistance?
>   - Coil voltage?
>
> To make things interesting find me a relay that:]
>   - Meets the needs above,
>   - Plugs into a socket,
>   - Has at least 5000 V isolation between coil and contacts,
>   - Reliable to 1,000,000+ operations,
> and
>   - Where we can get such a beastie.
>
> GL es 73,
> Bill - WB1GOT
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