I installed a MIP 5000 for a customer, replacing their Centracom CRT. This has been without issues, but the most prevalent is a more-than-acceptable hum when the dispatchers transmits. Myself and one of our experienced techs had started troubleshooting this, with no result. He feels that it is coming from the Gateways, but have yet to definitively put my finger on the culprit. We went from using the individual power supplies that came with the Gateways to a common power supply to free rack space, which is the same set-up that we used for a customer we installed a MIP 5000 for just before this one that has the hum issue. I have to admit I got tunnel-vision when it came to which channels this was occurring on, as the 2 main Ops channels were my focus. I am going to confirm whether or not this is on all or a select few. All but one channel is using 2-wire, the other is 4-wire. The Gateways are connected to the resource radios over a 50 pair, which was re-used from the old console (no hum then), and runs from one end of the building (where the Gateways are at) to the other end of the building (where the resource radios are located). There are wireline Polyphasors that we re-used from the old console (kept in place).
My other tech had tried the original power supplies on 1 or 2 of the Gateways, with what he said was no change at all. We went through and tested our pairs, did find one bad pair, but the others seemed fine. I did install impedance matching transformers in-line at the radio side of the 50 pair to see if it would help, and of course, little or no change.
I'm sifting through the schematics for the Gateways (which are Tone), to see if there is something with the jumper configurations that I may be missing. I started with the factory recommended jumper configuration, and am now at the leased-line configuration (jumpers S4, S12, S13, S14, S17, and S18 are Out).
If anyone has any recommendations or suggestions, I'm all ears. I have some 4-wire Polyphasors I'm taking with so that I can try everything 4-wire. Also I'm going to try 1 run of CAT 5 and string it temporarily from the back room with the Gateways to the radio room to eliminate or qualify the 50 pair from the equation.
MIP 5000 Hum
Moderator: Queue Moderator
Re: MIP 5000 Hum
Hum is always fun to chase. Possible culprits are power supplies, ground loops, crossed pairs, unbalanced pairs, and open pairs. To find it, you have to divide and conquer. Is it on one position, or all positions? Is it on one radio, or all radios? If it's one position on all radios, it's either the headset, the usb headset jack(s), the PC, or possibly the AC outlet ground. If it's all positions on one radio, it's either the gateway, the radio, or the cable between them. If it's all positions on all radios, then there is an AC service ground fault or crossed neutral between the power for the radios and the power for the gateways, or there is a ground loop carried by the telco cable between the two points.