Why most repeaters don't use TX PL codes?

[archjeb]

Hello all,

Just a curiosity question here.

Why do most repeaters only use an RX PL code and not BOTH an RX and TX PL code?

The reason I ask, it seems like it would clean things up with some of us using multi-band radios which can be more prone to intermod...and our RX wouldn't come alive until we saw the PL code?


Is there a reason this is not common practice?

-J

 

[Captain Kilowatt]

Your receiver is always alive. The PL tone just opens up the squelch. Some repeaters do pass the PL tone thru so you can take advantage of that and set your rx tone to tbe same as the tx tone.

 

[W5LZ]

You're right you receiver would only come 'alive' when it received that tone. But, it would also never hear things that did not have that tone on it. That seems to be a contradiction in terms if you want to hear all that's happening. If your repeater is that busy, or if it's being interfered with, then it may be a viable option. Otherwise, you will miss more than you might believe. If you want to use that RX tone just to keep YOUR radio quiet, turn the @#$ thing off.
- 'Doc

(Can you tell I'm not happy with that 'Tone Squelch' silliness? If it's used correctly it's fine. If it's not used as it was intended then it's a way of making it harder on others to make it easier on yourself.)

 

[archjeb]

You're right you receiver would only come 'alive' when it received that tone. But, it would also never hear things that did not have that tone on it. That seems to be a contradiction in terms if you want to hear all that's happening. If your repeater is that busy, or if it's being interfered with, then it may be a viable option. Otherwise, you will miss more than you might believe. If you want to use that RX tone just to keep YOUR radio quiet, turn the @#$ thing off.
- 'Doc

(Can you tell I'm not happy with that 'Tone Squelch' silliness? If it's used correctly it's fine. If it's not used as it was intended then it's a way of making it harder on others to make it easier on yourself.)

OK. so maybe I'm a little clueless here or not connecting the dots.... which has occurred more than once :-O

But, there are times when you are traveling through the city where there is a lot of UHF noise...I mean a lot of noise. And if we had a PL tone set on the transmit side of the repeater, it would keep the squelch shut/closed so we wouldn't hear the noise.

I guess what I'm trying to get at here is..why don't we do that? Why is it the general rule of thumb is we only do it on the TX side to the repeater....but we don't do it on the RX side of the mobile receivers?

I appreciate the feedback so far, but I still don't understand a clear answer of why we don't set a PL code for the repeater to TX on / our RX side?

What is the downside of having a PL code set for the Receive if you ONLY want to hear the TX that is sending the PL code? (in this case a repeater that is TX'ing with a PL code too.).

Captain Kilowatt, you stated that some repeaters do this...but I guess this leads the question of, why do the MAJORITY not do this?

-J

 

[archjeb]

You're right you receiver would only come 'alive' when it received that tone. But, it would also never hear things that did not have that tone on it. That seems to be a contradiction in terms if you want to hear all that's happening. If your repeater is that busy, or if it's being interfered with, then it may be a viable option. Otherwise, you will miss more than you might believe. If you want to use that RX tone just to keep YOUR radio quiet, turn the @#$ thing off.
- 'Doc

(Can you tell I'm not happy with that 'Tone Squelch' silliness? If it's used correctly it's fine. If it's not used as it was intended then it's a way of making it harder on others to make it easier on yourself.)

hmm...I guess you could look at it that way...but I want to filter to hear what I ACTUALLY want to hear. That meaning, if you are not TX'ing on the PL code that I'm expecting...I want to filter the audio. Heck, if you are in a metro area, then generally you should only be getting the repeater audio...so anything else is going to be noise (i.e. we have a band plan here....). How else do you filter the noise? Especially with multi-band radios, many of them the front receive/filters are really wide, and they are prone to a a lot of noise. So the only easy way I see to filter, is with a DCS/ or PL code. If there is a down side to taking this approach, I'm all ears. In the meantime, I still don't know why the majority of repeaters only use an RX PL code and don't in addition TX a PL code. So if someone has some enlightenment on this that they can share, this would be much appreciated....


-Jeremy

 

[hookedon6]

OK. so maybe I'm a little clueless here or not connecting the dots....

the main reason it that most controllers will not re-transmit a "clean" PL tone they do not completely strip out any tones from the user input and the will transmit a "hum" when the PL encoder is active.

also, using PL encode tones and DTMF tones for controller access often can not both be done a the same time.

 

[Captain Kilowatt]

The PL tone is supposed to be injected at about 10% deviation but nevertheless I have heard many show up on the airespecially the higher tones above 200 Hz.

 

[archjeb]

So, I started building a repeater and set a PL tone (the same) on the RX and TX side and interestingly, I got a weird loop where the RX side would stay squelched for 10's of seconds.... (like 30 seconds). It sounded like the buzzing/hum sound that you mentioned earlier.

At first I thought maybe it was the duplexer feeding back in or something, but then I removed the TX PL tone on the repeater and it all works fine.

So I guess that answers my question....PL TONE only on the RX side of the repeater.

-J

 

[Captain Kilowatt]

The original idea for PL tone access to a repeater was to keep from bringing up two repeaters operating on the same frequency at the same time in areas where their coverage may overlap especially during a band enhancement. Older gear could tx a PL tone but often had no such decoder for the rx end. Going back far enough you could buy kits that could be installed either in the radio or external to it that would provide PL encode but not decode. My answer to the intermod problem,which is what you have, is better frontend filtering not PL tones. My old Icom IC-2000H performs wonderfully on 2m even in "RF Alley" as we call Geizer's Hill in the city. Thats where all the high power TV and FM stagions are along with God knows how many paging systems and PCS systems.

 

[exces3]

PL tones have a long history in 2-way
commercial FM. Once upon a time,
there could be a Fm channel for dispatch,
with several unrelated base stations,
hundreds of cars each, in a close together area,
so dozens of different PL tones were needed.

Tx and RX PL tones were not necessarily the same.
TX PLs could be switched to alert different groups of cars, etc.
..................
Ham radio, being less crowded,
the issue is to avoid lighting up a repeater
that you don't intend to.

I suppose it is possible that you could be in an area that
receives two repeaters on the same freq, ..
the repeater operators are unlikely to be concerned.

 

[RatsoW8]

Commuting back and forth to Chicago for 8 years I also noticed that some of my radios were more prone to intermod than others and some were useless once I was close to the city. Repeater ops are not going to take that into consideration for using tones to open my squelch. It was up to me to find the gear that was least susceptible to intermod interference. The 2m/70cm rig that worked for me was the Kenwood TM-V7A.

 

[Captain Kilowatt]

My old Icom IC-2000H is nearly bulletproof. It is just a 2m rig but has wideband receive. It is based on a commercial platform that Icom ised for it's busimess band radios and IIRC it has a tracking frontend meaning that while it is wideband the frontend is relatively narrow but tracks with tuning.