Why can't I key up 145.47?

WHY CAN’T I KEY UP 145.47?

 

Have you tried to key up or talk on 145.47 and cannot?  Well, unfortunately, I have had to add a tone board to the repeater receiver. What does that mean? It means that when you transmit, you must also transmit a 100 Hz sub audible tone with your signal in order for the repeater receiver to “open up.”  Many of you understand this practice. But for those who may not be familiar with it, I’ll give a brief tutorial.

 

While not as common on amateur radio repeaters, tone squelch has been a staple of the land mobile radio world for years.  It was developed in the late fifties or early sixties. Your local police department or public safety agency’s radios have tone squelch.  They use it to insure that only their users access the repeater, and NOT other users that happen to be on the same frequency.  Like our amateur frequencies, they are shared, but unlike our amateur frequencies there are FCC sanctioned coordinating bodies to (hopefully) insure that the users of the same frequency are separated by some distance.  Land-mobile frequency coordination, unlike our volunteer coordinators (SERA), is mandatory before a license to operate is issued. Even with this frequency coordination, it is still necessary to keep users separated in these “closed” systems.  The term Tone squelch goes by several names in the commercial radio world:  Motorola calls it “private line,” GE called it “channel guard,” and RCA called it “QC (quiet channel).”  In later years, Motorola developed a digital counterpart for tone squelch that the called “digital private line” or “DPL”. Even today’s trunked radio systems use a version of tone squelch or digital tone squelch.

 

In early years of amateur repeaters, a repeater that utilized a tone squelch was considered a “closed” repeater.  Only the authorized users were given the tone frequency to access the repeater. I’m not sure what kind of honor system they were using, as the purpose of the closed repeater could be easily sidestepped if someone decided to share the tone frequency with a friend.  More recently, repeater owners have used tone squelch to mitigate co-channel users of other repeaters from accessing their repeater. Amateur repeater frequencies are also shared, meaning that a repeater in the Knoxville area can be sharing the same frequency in another area.  There are 145.47 repeaters in Nashville, Winston-Salem, and Atlanta. Tone squelch is sometimes used to keep the users of the “distant” repeater from accessing the “local” repeater, and vice versa.  It doesn’t mean that either repeater is “closed.”

 

Another use of tone squelch is interference mitigation.  That’s what I am doing with 145.47 right now. I am using the tone to keep the interference from the TV station from keeping the repeater keyed up with the loud squealing noise that I’m sure you have heard by now.  I have also had to place a tone decoder on the 146.625 earlier this year when it experienced a similar kind of continuous interference.  However, I’m happy to report that the 146.625 problem is gone now.

 

Now, here’s the caveat:  Just because you can’t hear the “other” repeater’s user(s), or the interference, it doesn’t mean the interference is gone. It is merely masked,  or muted. What does that mean?  It means that if your  signal is not strong enough to overcome the offending signal, it still won’t bring up the repeater, even if the desired signal (yours)  has the right tone. This means that if you are using a hand-held portable or your signal is weaker than the TV interference, your signal won’t make it thru the repeater.

 

It is my belief that the 145.47 repeater will not need to have the tone squelch on it for the long term.  As soon as the TV interference is mitigated, I will remove the tone from the receiver and return .47 to its normal “open squelch” state.  Certainly, it makes it easier for travelers and those who don’t have tone units on their radios to enjoy 145.47.  I have remote control of the repeater’s tone board, and have turned it off occasionally to check the repeater receiver status.   In the meantime, please understand that even if you have your tone encoder on and selected to the right frequency (100.0 Hz), you still may not be able to access the repeater as easily as you did before this TV interference problem started.  I promise you this will not be a permanent problem. The staff at the TV station and I have discussed several options to (hopefully) reduce or eliminate the offending signal that is causing the “mix.”  If you are unfamiliar with what is happening to cause the problem with 145.47, please read the prior blog entry and it will bring you up to date. 

 

What else is happening in the WB4GBI repeater world?  As you read this, the NEW duplexer for 146.73 is being tuned.  As soon as it arrives in Knoxville, I will take it to English Mountain and install it! I am convinced that 146.73 will see a drastic improvement in its coverage when the new duplexer is installed.  I will post in the blog as soon as the duplexer installed.  

 

Thanks again for reading!

 

73 de Tim WB4GBI