PTT connection to MX-P50M amp drops noise floor?

Heath Petty

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Jan 14, 2022, 1:46:31 AM1/14/22

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I noticed something this evening when I was getting my newly acquired MX-P50M amplifier working with my HL2. If I connect the PTT connection directly to the EXTTR port on the HL2, when I turn on the amp my noise floor drops about 20db. I can still hear signals come through, and everything seems to be working fine. When I have the PTT line disconnected, or going through a radio-dan PTT controller box I don't see this (the ptt controller box isolates the PTT lines). I measure the voltage across the PTT connector from the amp and it read -13v (with positive lead on connected to the red wire, and ground connected to the black wire).

I am trying to figure out what this is telling me, and hopefully not causing damage to the HL2. I didn't see anything out of the ordinary with the direct PTT connection, so I went ahead and made an FT8 contact - just to test things out. Is this telling me that I need to review my bonding setup at home, and that could be contributing to my high noise floor?

Heath

KL0PC

Steve Haynal

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Jan 15, 2022, 12:28:47 AM1/15/22

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Hi Heath,

From the point of view of the HL2, is the center pin of CN1 on the N2ADR board (The EXTTR switch) 13V above or below the shield (GND) of CN1? I'm not familiar with the MX-P50M and am wondering if they expect a negative voltage here to be shorted to ground. The HL2 may not be able to handle that.

73,

Steve

kf7o

Heath Petty

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Jan 15, 2022, 10:41:16 PM1/15/22

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Yea, the pin is 13v below the shield (i.e. -13v). It looks like I did not cause any damage to the HL2, but I wonder if the wires on the amp are reversed (I have found this way too many times on electronics that come directly from China). I'll probably continue to use the radio dan keyer as well. Thanks for the reply.