CTCSS Reverse Burst Incompatibility

wb6fly · Post by **wb6fly** » Sun Mar 24, 2002 11:15 am

I manage a simplex VHF system comprising about two dozen portable, mobile, and base radios made by M. All radios are late-model programmable units, and all are set to both encode and decode 136.5 Hz CTCSS. I then added a similar radio made by K to this system, and I found that a squelch tail was heard on all M radios whenever the K radio ended a transmission. All radios, including the K, send a reverse burst at the end of each transmission, and the CTCSS deviation is exactly the same.

I looked at TIA/EIA-603, the international standard that both M and K obey, and I found that there are TWO reverse burst formats in use: One format advances the tone phase 120 degrees for 180 milliseconds, while the other format advances the tone phase 180 degrees for 150 milliseconds. Since all radios in my system use digital signal processing to encode and decode the CTCSS tones, they work only on the native format and ignore the other. Since M and K did not choose the same format, the two brands have reverse burst incompatibility. Of course, each company's tech support denies that there is a problem, and suggests that the other brand's radios are not set up properly.

I'd like to know just how widespread this problem is, and where I can lay my hands on the flash upgrade that K supposedly has created to make their reverse burst the same as M's. The K tech support doesn't admit that there is such a thing- or a need for it!

Chris · Post by **Chris** » Sun Mar 24, 2002 11:54 am

That is a known problem with Kenwood, make them fix it. It is a software fix that they do at their depot. Other issue with Motorola radios is that they require a slightly longer turn off code duration than other manufacturers.

jim · Post by **jim** » Sun Mar 24, 2002 12:53 pm

....or tell them to get rid of the Fisher Price radio and buy a Motorola.

...just kidding (:

Josh · Post by **Josh** » Sun Mar 24, 2002 1:51 pm

The problem is very widespread.

I get it when trying to use a cheap Spirit/M series radio with Radius units. I hate it, so, I don't use the Spirit/M series unit anymore!

I found that Uniden radios (their PRC line) is totall compatible with Motorola PL, except with OLD Motorola repeaters with short 'reverse tone' times.

DPL on the otherhand, seems compatible on all levels.

-Josh

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Sun Mar 24, 2002 2:10 pm

On 2002-03-24 16:51, Josh wrote:
...DPL on the otherhand, seems compatible on all levels...

Well, it should be.

DPL sends a 134Hz 180ms turnoff code at the end of transmittions, which squelches the reciever.

Will · Post by **Will** » Mon Mar 25, 2002 12:15 am

This problem dates back about twenty five or more years. On some Motorola radios in the RSS it gives you a choice of "Muting", set to OR to enable carrier or PL loss to mute receiver.
It gets lots worse using different radios on Quantar repeaters, they "crash" real bad.

Glen W Christen · Post by **Glen W Christen** » Tue Mar 26, 2002 1:28 pm

The reference to 136.2 on PL brings up another problem. If a co-channel user is using DPL the turn-off code will momentarily open the PL and be very annoying.