Scott, A proper answer must address the differences in the way Amateur and commercial radios encode and decode the PL (CTCSS) and DPL (CDCSS) tones. Generally, commercial-quality portable and mobile radios can encode or decode both schemes well. Again generally, most Amateur-grade radios can handle PL fairly well but not DPL. The issue here is the inability of most Amateur-grade radios to encode and decode the reverse-burst squelch-tail elimination (STE) signals. It is one of life's great pleasures to have a radio mute silently at the end of an incoming transmission, without so much as a "tick" instead of a crash. However, in one of life's inexplicable ironies, there are Hams who walk among us who delight in hearing squelch crashes, and can't seem to survive without them- must be fans of the old Highway Patrol TV series.
The CTCSS reverse-burst STE uses a phase shift of either 180 degrees or 120 degrees (both are officially-recognized formats) to activate the muting circuits of the receiver, but the CDCSS scheme uses a brief burst of 134.4 Hz tone to accomplish the same effect. And therein is the problem with DPL- the same mute tone is used with ALL digital codes, so a co-channel user with DPL (or a CTCSS user with a nearby tone like 131.8 Hz) can mute your receiver inadvertently. Some of the cheaper Amateur-grade radios- Puxing and Alinco come to mind- use less-sophisticated methods to generate tones, and these tones sometimes are distorted enough to cause intermittent operation of CTCSS or CDCSS decoders. Perhaps "crude methods" would be more accurate. A 3-step approximation of a sine wave (the cheap and easy method) is a good example of crude, and is raspy. But, I digress. If the radios and stations you plan to use are capable of handling PL and DPL, go for it. I suspect that PL operation will be able to operate well with a greater number of portable and mobile radios. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of kq7dx Sent: Wednesday, February 24, 2010 12:43 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] New to 900mhz,, PL or DPL? Hello to the group, I have had a couple of really nice hams try to explain this to me but I am not getting it. Which is better. Most importantly which is better in a metropolitan city with lots of RFI and noise on the bands. Particularly 900mhz. I have seen mostly PL and just a few DPL listings so I am not sure that it is RFI motivated for the selection. So which is best for a repeater application. The receiver for the repeater will be a 800mhz Maxtrac converted to 902mhz. Thank you for your help, and if this was covered on another post please let me know. I am on a dial up and it is hard to research. 73s scott
