PTT Switch & CB Radio

[mtrevelino]

I relocated my cb to the left handle bar using a RAM mount. Now for the latest problem. The CB squeals while transmitting. The only thing is that it still squeals when I turn off the engine but keep everything powered. I am now thinking that it may be getting feedback through the PTT cable(s). I figure that the PTT switch runs along the handle bar to the Autocom unit where another wire runs up and plugs into the cb. If I unplug the PTT wire from the cb and hand press the transmit button on the side of the cb, it does not squeal. What is the thinking on this? Do I have to move the cb to the other handle bar or can I shield (how?) the PTT switch cables? Any thoughts and suggestions is greatly appreciated!

I do not think that a ground isolator would be the fix for this problem.

[mtrevelino]

No takers yet! I tired something. I have a extra PTT wire and connected it directly to the Autocom (bypassing the wire route along with the other wiring. It still squeals. I have heard that the Flashtek HID may put off some interference, but I do not believe that this is the cause. I will try disconnecting it and see what happens. Suggestions please!!!

[mpillis]

I had the same problem with the ptt and my baehr. I have the ptt on the left handlebar and running under the stingray then down left side of tank to just under the seat. when I had the wire under the seat on the left side I had the same awful squeel. Once I ran the cable excess across under the seat to the right side of the bakie and tucked it in there, no more squeel. Just play around with the excess cable and find someplace to tuck it where you have no squeel. Worked for me, Good luck

[used2jeep]

(I don't have a KLT yet but I do have an Autocom and Midland handheld cb) Did you reroute the PTT near anything major when you switched sides?

[GBaker]

This is a major pain in the patuky. I have an '06 with VOICE COM II and battled it with a Midland CB and even with the recommended Kenwood GMRS/FRS. The Kenwood works fine in the oddiment box or in the tank bag to the right of the stingray anywhere else and it just buzzes or squeals. The CB when plugged to the bike power via a fused accessory plug wired straight to the battery and hooked to the bikes CB antenna works great with a portable earbud and ptt mike plug straight to the radio but if I plug either the speaker or the mike or both to the VOICE COM II I can hear thru the helmet head set but when I push the PTT it buzzes. When plugging to the VCII I use the modified cables. (SEE ATTACHED upper right corner)

I think it has to do with not only interference from either the electronic ABS/ignition etc or most probably a ground loop some where. Finally got fed up and ordered the dang BMW CB.......

[mtrevelino]

Still tinkering with this thing. This morning I installed batteries in the cb to give it a try, the squeal is still there. Could it be the location of the cb (antenna interference)? Maybe it does not like to be mounted on the left handlebar. Yesterday I disconnected the HID to see what would happen, nothing! I ordered some "shielding" tape in which I will tape the ptt cables to see what happens. What gets me is that it does this with the bike not running.

[UncleMark]

This is a major pain in the patuky. I have an '06 with VOICE COM II and battled it with a Midland CB and even with the recommended Kenwood GMRS/FRS. The Kenwood works fine in the oddiment box or in the tank bag to the right of the stingray anywhere else and it just buzzes or squeals.
Had the same problem... I ran the radio all around the back of the VII unit on the outside of the oddy box. Noise like all get out. Seemed very prominent around the helmet jack. Inside the oddy box, no problem. Using clear 3M dual lock, I mount the Kenwood radio on the top of the oddy box right in front of the lock. No squeal and great reception. :cool:

[mtrevelino]

This afternoon I tried connecting the bmw antenna to see if possibly the antenna was creating the squeal. It was still there. This week I should receive the copper foil shielding tape. Next weekend I will try taping the ptt wires and the helmet cord since they run along side one another. After that, it will be dishing the cb if it still squeals.

[pharmerphil]

I googled onto bmwlt.com because I was having radio issues. Tried the suggested procedure (disconnect battery) and am feelin' good! Even a beemer sucks without some good sounds.
I gladly signed up and paid for a year.
Where I am in eastern Oregon, even minor service is a major issue.
Thanks for the site!
Phil http://www.bmwlt.com/forums/newreply.php?do=newreply&noquote=1&p=205145#
Smile

[scarver]

Yes, getting the CB to work is a challenge. Welcome to the world of ground-loop isolation.

Have an Autocom Pro-7 system on my R1200RT and have three tranceivers I can hook into it via a switch mounted within reach while riding. These are the Kenwood TM-D700A ham radio, the Kenwood TK3101 GMRS radio, and the Cobra 38WXST CB radio. Use the Autocom PTT switch for all three. Have a bike mounted CB antenna, i.e., it is grounded to the frame. Built a special interface box placed in-line with the 1433 cable from Autocom.

Attached below is a matrix of results collected for another RT owner in Atlanta plus the schematic of the interface box. The key is to isolate not only the Mic and Spkr circuits but also the PTT portion. One must keep the Autocom ground isolated from the bike ground.

[mtrevelino]

Continuing on with my cb system. I dug out my Midland 75-822 and installed it in the oddments box. I shielded (with foil tape) the ptt wires and the Autocom 1433 cable. Turned the key on without starting the LT and the squeal is still there while trying to transmit. If I touch the cb antenna while trying to transmit, the squeal noise will be cut in half. So it looks like I will be just listening with the cb. Any other suggestions????
I also installed the mic-o-pegs today and the saddle bag running/turn signal lights. Getting ready for CCR!!!!

[scarver]

Redrew the schematic of the Ground Loop Isolation (GLI) circuit since it is much easier to understand than the version posted earlier in this thread.

The reed relay is a critical part of the interface box: it isolates the PTT line and is what enables you to use the Autocom PTT. The green isolation transformers are not in the box; I used a couple of other isolation transformers I had handy. I do use the RS isolation transformers in another interface between the Autocom and a Kenwood D700A ham radio.

The project box is a RS 270-1801 'Project Enclosure'. Parts were mounted on half of a RS 276-150 'Grid-Style PC Board'; it slides nicely into the slots of the box.

Note: Used a socket on box instead of second half of Part 1512; needed to mount box outside for space considerations - not enough room under seat.

[mtrevelino]

My squeal is gone! I replaced the stock bmw antenna with a firestik DS14FG non ground plane antenna. I was able to use the stock antenna mount, I just had to get a longer screw for the new antenna. I still need to better adjust the SWR, but this will get me through CCR week. I want to thank everyone for suggestions and especially SCARVER (Herman) for his ground loop isolation box.