Thanks for the reply. The 38A sounded really good until I started to try to program and install it. The more I fool with the thing, the less I like it. After getting all my levels set up, I sent varying frequencies starting at 200 HZ and going to 3 KHz to check the response. I noticed a roll off above about 1.5 KHz even though I have all jumpers and switches set to "flat." Upon checking with a scope, I find it is occurring in the 38A. I also noticed that the audio through the repeater isn't as "crisp" as it is on direct. Of course it is also passing through a receiver and transmitter but I kind of think that 38A is causing some of the problem. I really wanted to get this thing on the air next week but I am seriously considering scrapping the controller altogether. I have a TS-64 I can use for PL decoding and encoding and I think I saw a Com Spec IDer around. I also think there is a CAT200 around but I am not too fond of them either. Looks like decision time.
--- In Repeater-Builder@yahoogroups.com, "Eric Lemmon" <wb6...@...> wrote: > > You have discovered one of many "dirty little secrets" that apply to > aftermarket tone panels. When designing the 38A tone panel, and many other > products, Zetron overlooked the fact that reverse burst is essential in the > repeated audio. From a close examination of the 38A manual and schematics, > it appears that it will decode CTCSS reverse burst and CDCSS turnoff code, > and MAY generate CDCSS turnoff code, but I see no evidence that it can > generate reverse burst. That alone is a major shortcoming! > > Zetron is not the only manufacturer that ignored reverse burst encoding when > designing a community repeater controller. Instrument Associates, which > produced the i20R "On-site Repeater Controller" for the Motorola GR1225 > desktop repeater, did likewise. I did not realize this until I found that > squelch crashes were immediately heard as soon as I put the i20R in service. > Although some fans of the old "Highway Patrol" shows starring Broderick > Crawford may enjoy the sound of a squelch crash, I do not, nor do any of my > radio users. That i20R was pulled from service immediately, and put on the > shelf! > > There are two different formats for CTCSS reverse burst STE (Squelch Tail > Elimination) that are defined in TIA-603-C, the international standard for > land-mobile radio performance and design. One format, used principally by > Motorola, uses a 120-degree phase shift, while the other format, used by > Kenwood and many others, uses a 180-degree phase shift. Since modern radios > often use digital signal processing to encode and decode low-speed data > (CTCSS and CDCSS), it is all too easy to design a circuit that responds > perfectly to 180-degree phase shift but ignores 120-degree phase shift, and > vice-versa. Zetron and others couldn't be bothered to create a CTCSS > encoder that could be switched between the two reverse-burst formats, so > they just ignored the problem. > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: Repeater-Builder@yahoogroups.com > [mailto:repeater-buil...@yahoogroups.com] On Behalf Of wspx472 > Sent: Wednesday, November 18, 2009 10:15 AM > To: Repeater-Builder@yahoogroups.com > Subject: [Repeater-Builder] Zetron 38A not sending reverse burst > > > > I am trying to get a repeater going using a 38A and find that it doesn't > send reverse burst. I thought I saw that it did in the manual but upon > looking again, all I see is where it responds to reverse burst. Does anyone > know for sure if it is supposed to send reverse burst? If so, how do I get > it to do it? >
