Mike, If the repeater system was working fine, but suddenly got hum without any action on your part, I'd start looking for a failed bypass capacitor. Try turning off AC power to the facility at the main breaker while the repeater is on battery, and see if the hum goes away.
Sometimes, an arrestor on the high-voltage (usually 12,000 volts) side of the utility transformer will fail, causing a current to flow through the grounding system. This can cause dangerous voltages to appear on the neutral and grounding conductors, and will cause hum to suddenly appear in sensitive circuits. What frequency is the hum? 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Mike DeWaele Sent: Sunday, October 19, 2008 5:29 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Ge mastr 2 link question Paul, Eric Thanks for the response. I did some more testing with your suggestions. I tried hooking both radios up to a deep cycle battery. The hum is still there so I think that rules out the astrons! The audio from the main repeater to the link isn't as bad as from the link back to the main repeater. Both have a hum to them however the 2 meter to the 440 you can hear the voice. the other way all you get is the hum. For testing I have it on the bench in the basement. the only common connection is only the audio and tx lines between the two radios. I have also tried it with a common ground as suggested by NHRC in the controller directions. Both have the same results. I want to make sure it works here before it goes back to the hill. At the site it's just my radio equipment and Wifi internet which has not given me any problems with both machines working there prior to bringing them to my house to work on this linking project. Maybe tomorrow I will give NHRC a call and see if they have run into this problem before. Thanks, Mike KA2NDW -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] Behalf Of Paul Plack Sent: Sunday, October 19, 2008 4:59 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Ge mastr 2 link question Ditto the possible issue with the Astrons, but you may also have too many common grounds. If you have the grounds of the machines interconnected through (1) the power supplies, (2) antenna and/or feedline bonds, (3) rack rails, (4) through the linking cable and (5) an additional, "just to be sure" ground strap between the radios, you could very easily have a ground loop. Since all the interconnections are made using unbalanced audio lines, you can't just lift the ground at one end as we might try in the pro audio world. Sometimes, a cheapo audio transformer, like the 600-ohm isolation transformers from Radio Shack, are enough to alleviate the loop, because they allow you to leave an audio ground floating from the chassis at one end of the link cable. A quick, cheap investigative tool here is one of the old three-into-two-prong AC plug adapters. If you use it to lift the ground pin on one of the Astrons and the problem goes away, it will be an important clue. Good luck! 73, Paul, AE4KR ----- Original Message ----- From: Mike DeWaele <mailto:[EMAIL PROTECTED]> To: Repeater-Builder <mailto:Repeater-Builder@yahoogroups.com> Sent: Sunday, October 19, 2008 1:30 PM 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
