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                        January 31, 1975

HD-15                                           Bulletin No:

Phone Patch                                     HD-15-1



                             Service Notes



The major complaint is not enough isolation between transmit and receive

circuits.  This results in cycling between transmit and receive when

attempting VOX operation.  Replacing the hybrid transformer could be

tried, but this usually does not cure the problem.  Sometimes the VOX

gain in the transmitter is adjusted too high.  When the unit is

determined to be operating satisfactorily, try to convince the customer

of the advantage of push-to-talk operation.  "You have control over what

is being said, and you will also prevent both parties from doubling, or

talking at the same time."



The VU meter indicates only signal from the receiver into the patch.

Customers seem to think that the VU meter should indicte when a signal is

being fed from the phone line into the phone patch.  This is not so.  In

the case of the HM-15, a -10 VU level appeared to be giving satisfactory

operation.

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                        January 23, 1978

HD-15                                           Bulletin No:

Phone Patch                                     HD-15-2



                    Phone Patch/Bell System Interface



The HD-15 Phone Patch is not registered with the FCC for use directly

with telephone lines.  The Bell System will require a special line

couple, model QKT, for connection to their lines.

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