Raspy 60Cy hum on transmit- IC706

[wb7ely]

Hello-- I am having one heck of a time with the IC-706 Separation Cable modification. I consider my self a fairly good technician but I cannot get the separation cable to work. Even taking the RRC out of the loop and using a double female RJ 45, I am getting a raspy loud hum noise on my transmit audio as monitored on a sep receiver. I have checked the continuity through the two  cables  terminated with RJ45s and all is good. I read that the radio side pigtail should be short to reduce interference and mine is 3ft total.
Question:
Is the modified cable (radiio) @ 3ft too much?
Could that be causing the loud hum?
If the two shields (white shield and red shield) touch, is that bad?
Should the separation cable ("drain?) wire be connected to the station ground?

Any wisdom would be greatly appreciated.

De WB7ELY




 witha 2 ft

[wb7ely]

Guys-- Here's some additional troubleshooting info:
- The RRC's perform fine with the IC706 -all functions work great ..except for xmit audio.
- I am running (JT65) digital mode.
- There is a raspy 60 cy tone on top of the modulation when running the RRCs.
- I am monitoring this on a separate receiver (with a 2 ft antenna) 50 ft from the main vert antenna
-The modified separation cable works fine when each RJ-45 is connected to a double female connector and the radio run without the RRC's in the loop.
-I have shortened the radio-side sep cable to 15"
-The problem occurs whether I am connected to a dummy load or not.
- Should I give up,dump the 706 and buy a K3?

-any thoughts would be helpful-

Thanks
De Dave WB7ELY

-

[wb7ely]

What about Ferrites to stop EMI from entering the RRC?
Troubleshooting indicates theRRC is getting some EMI into it. The 1258 manual states to keep the radio to RRC cable short due to hum may be interoduced. Is this what I am seeing?
My favorite surplus store has these clamshell ferrites on sale for a buck: http://www.mpja.com/040in-ID-Ferrite-Clamshell-EMI-Filter/productinfo/17842+FL

1-Has anyone used these ferrite filters in an installation with RRCs?
2-Would this be the logical next thing to try?
3-I am thinking I should install one of these on each wire going to the radio-side RRC?

sign me
...still cannot get on the air
DE Dave WB7ELY

[sm2o]

There is no hum from a IC-706 setup if the cable and strappings are done correct. I guess you have a screen which is broken. Measure the cables to be sure that all screens and wires are connected, and that there is no shortcut between the different pins. Check the red straps with an ohm meter, they may be broken inside the red plastic. If all connections is OK try to use a separate PS for the radio and RRC, or if you do that try to use the same. Ferrits do not help against hum, they may help if you have RFI, but it's always better to keep the RF out of the shack than trying to get rid of it when it's already inside.

73 de mike

[wb7ely]

Thanks Mike-- Checked the modified separation cable again.
1- All conductors check good pin to pin,  higher resistance than I'd like: (0.5-0.9 ohms)
2- Screens show OK especially the red screen (copper )
3- Connected the modified sep cable with double female RJ45 between radio and front panel and monitored transmitted audio, it was clean.
4- There is no RF in the shack, antenna (no radial vert) is 50 ft away
5- Checked the small red jumpers  in both RRCs, all are good.

De Dave WB7ELY