Mike, Using two separate power supplies might be part of the problem, especially if they are not on the same power phase. Many Astron power supplies have the negative terminal grounded to the chassis, which can allow AC hum to ride on the DC output. If the hum you hear is 120 Hz, that is usually caused by a full-wave rectifier's ripple. If 60 Hz, it is usually a grounding issue.
The first thing I would try is to substitute a fully charged lead-acid or gell-cell battery for each Astron power supply, to see if the hum remains. Do not ground any of the negative leads when you perform this test. If this problem occurs at a commercial site, it usually is caused by a power neutral being grounded in a sub-panel by a poorly-trained technician. Besides being a violation of the National Electrical Code, such a condition will almost always result in AC currents flowing in the grounding system- a no-no. When audio circuits are connected into the grounding system, some current will flow through the cable shields and be induced into the audio chain. If the hum goes away when on batteries, try clipping the ground jumper from the negative terminal, inside each Astron power supply. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Mike DeWaele Sent: Sunday, October 19, 2008 12:30 PM To: Repeater-Builder Subject: [Repeater-Builder] Ge mastr 2 link question Hi All, I'm having a problem linking two mastr 2 radios together. I have one site and want to full time have my 2 meter and 440 machines linked together. Equipment : (2) Astron R-35 power supplies (one for each machine) (1) Duplexed GE mastr 2 mobile for 2 meter machine. (1) duplexed Ge mastr 2 mobile for 440 machine (1) NHRC-4/M2 controller installed in the 2 meter radio (1) cord made up out of 2 mastr 2 cables Both units were tuned up and working properly as independent repeaters before attempting this project. Then we started the linking project! The radios are linked via the made up cord with the 2 meter machine being the main repeater and the 440 as a slave repeater on the secondary port. The set up works properly on both ports in both directions. The id sounds fine and the courtesy tones are fine. The problem is the repeat audio in both directions has a humming noise that almost sounds like it is being over driven. We have adjusted levels on both the controller and discrimators in both radios to no avail. We do have a common ground between both radios per the instructions with the controller. I'm thinking there is smething that needs to be padded in the audio lines. I'm researching the web but if any one has gone before me with the same project I was hoping to save some time. Thanks, Mike KA2NDW
