Thanks Skipp I will take a good look at the audio cables. This configuration has worked well for many years and we added IRLP a year ago but it is external. The hum is not present when you kick over the repeater and let it ID. It is only present when a signal comes in on the receiver. So first guess is it's all OK under transmit so ripple on the power supply is doubtfull. The Audio from the controller must be fine also. I suspect the audio cable from the receiver or some other cable has come loose and lost it's shield. I will post what I find. Bill N5ZTW
----- Original Message Follows ----- From: "skipp025" <[EMAIL PROTECTED]> To: [email protected] Subject: [Repeater-Builder] Re: Hum on MSR-2000 Receiver Date: Sat, 09 Aug 2008 17:08:31 -0000 > I've seen this before on an MSR-2000 or two... or > twenty... > > It might be related to the added interconnection cables. > What kind of wire are you using from the receiver to what- > ever external devices (repeater controller) you have > connected? > > The black multi conductor round wire found and used on > older Motorola Desk Mics and remotes is pretty much the > only wire I use on any critical analog communications > project. The brown wire within the cable is very > specially shielded for low level audio applications and > it makes a BIG Difference in many applications. I found > out the hard way when wiring many different types of > external tone and trunking controllers onto the MSR-2000 > repeater back plane. > > I could actually see induced noise when using other high > quality cables... so I went back to using only the > Motorola black mic cable and have never had an external > device hum problem. > > Motorola used to sell it separate to the mics as available > wire and of course they no longer do. You could steal the > wire off a used Motorola Desk Mic. I've compared the wire > to other shielded wires and for some magic reason it > works better for the application not to mention the color > codes match the Motorola function codes I standardized > on. > > If you trouble shoot the problem to the applied wire and > are not able to locate the mentioned black mic wire... > you're welcome to contact me direct about it. After mucho > searching I found the mfgr and became a Dealer. If you > have a short run... I might have some around to ship you > for the cost of the postage. Otherwise it does cost > between $1 & $2 a foot.. but it does work very well. > > Might be something else... but the external repeater > controller wiring is something I've had to take an evil > eye look at more than once. Something in your original > setup might have changed/moved to start-up the hum > problem. Sometimes what ever caused the hum to start up > is not an easy "figure out". > > One quick generic test to source tired power supply caps > (ESR)... at the repeater site remove the exciter > connection from the RF Power Amplifier and terminate it > into a proper load. Key the repeater with the terminated > exciter and listen for the hum with the PA not drawing > much current (being used). If the hum goes away... you > might have tired filter caps or induced RF causing the > hum introduction. > > cheers, > skipp > > skipp025 at yahoo.com > www.radiowrench.com/sonic > > > "Bill" <[EMAIL PROTECTED]> wrote: > > > > Howdy group. > > I have a Motorola MSR2000 repeater on the ham bands that > > I maintain. VHF 147.32 in Austin (Oak Hill)Texas. > > It has developed a hum on the receive signal. I know > > it's the receiver as there is no hum when the machine > > ID's with no input from the receiver. The hum has been > > getting worse and now I need to take a look. I have > schematics and instruments. I'm asking to see if anyone > > has seen this kind of issue before. I run a 114.8 PL > > but it sounds more like 60Hz not 114 hz I'll have to > > look at the audio and measure. The machine is on IRLP if > > anyone wants to take a listen the node is 3364. Any > input would be helpful. Jim K5VPW monitors the machine and > > runs the IRLP node so he may be listening and is willing > > to assist. Bill N5ZTW > > > > >
