Go Back   WorldwideDX Amateur Radio Forums > Amateur Radio Related > VHF/UHF Bands and VHF/UHF Rigs

Amateur Callsign Lookup
Enter Callsign:

Repeater Channel Spacing with Digital & Analog Repeaters?

Like Tree1Likes
  • 1 Post By W5LZ

LinkBack Thread Tools Display Modes
Old 02-22-2012, 05:26 PM
iTrader: (11)
Join Date: Apr 2002
Posts: 8,178
Moleculo has disabled reputation
Default Repeater Channel Spacing with Digital & Analog Repeaters?

I've been trying in vain to coordinate a frequency pair for my D-Star repeater. (I will have a lengthy rant about the effectiveness of the local coordination body in another upcoming thread.) Since I'm not getting any help, I'm going to have to pick my own frequencies, put the repeater up uncoordinated, and do my best not to interfere with the coordinated repeaters.

I want to make sure I understand the bandwidth characteristics of D-STAR before I finalize my pair. For reference, I've studied this page, which has some very good information on real tests that they've performed on the bandwidth usage of D-STAR as compared to a typical analog signal: The Utah VHF Society - D-Star channel spacing recommendations

Here's an interesting spec analyzer plot showing D-STAR on the left and analog on the right:

In the summary table on that page, they show that the typical -30db bandwidth for D-STAR is about 11khz and -55db bandwidth at about 14khz. They go on to recommend a minimum channel spacing of 12.5khz for D-STAR segments of a coordinated repeater plan, although they said that you could get away with 10khz if it wasn't for random frequency stability issues present in most transceivers.

In Southern CA, the 70cm band is channelized into 20khz segments for repeaters like this: 445.020, 445.040, 445.060, etc. If I understand the spec plot above as well as the analysis on the referenced page, I think I should be able to squeeze a D-STAR repeater between two distant analog repeaters on a frequency like 445.030, right? If my TX -30db bandwidth is about 11khz, my D-STAR repeater would take up roughly from 445.0255 to 445.0355, right? If I'm reading their chart right, the -30db bandwidth of a typical analog signal is 17-18khz. So, if I squeeze my station between them, it looks to me like I'm more likely to receive interference from other repeaters than cause interference.

Am I looking at this correctly? The machines I have in mind of squeezing between are so far in the distance, I don't think it will be a problem even if I was right on top of their frequency, however I'm obviously trying to be careful if I have to do this uncoordinated.

Reply With Quote
Old 02-23-2012, 05:14 AM
Crotchety Old Bastard
iTrader: (0)
Join Date: Apr 2005
Location: Oklahoma
Posts: 6,915
W5LZ is on a distinguished road

I think the problem you have is that there are a limited number of usable 'channels' for a repeater (on any band), and the availability of on empty channel just isn't there.
A 'digital' signal is typically narrower than an 'analog' signal sure, but the difference isn't that great. That depends on just how well the transmitter is adjusted, which isn't going to be the best in all circumstances. So, that 2 Khz space between signal edges is probably the best compromise.
Squeezing between two allocated channels could be possible if propagation never changed (deals with the distance to that other two repeaters), but it does. You run into that with 'properly' coordinated repeaters quite frequently. I'm sure you can imagine what it would be like if you throw an uncoordinated repeater into that mix.
I don't know what the best solution would be. Maybe acquiring an already allocated freq.pair? And I can guess how likely that would be.
Good luck.
- 'Doc
Se7en likes this.

Reply With Quote
Old 02-23-2012, 05:27 AM
hookedon6's Avatar
W9WDX Amateur Radio Club Member
iTrader: (0)
Join Date: Jun 2008
Posts: 1,508
hookedon6 is on a distinguished road

well, all I can say is: there are 2 good days in a repeater owners life, the day you buy it and,.......

good luck dealing with the Kilocycle Kops

Reply With Quote
Old 02-24-2012, 10:53 AM
iTrader: (11)
Join Date: Apr 2002
Posts: 8,178
Moleculo has disabled reputation

In SoCal, 2m and 70cm are coordinated by two different coordinating bodies. Here's an interesting piece of information that I just discovered: The 2m coordinating body has carved out a piece of the band for digital repeaters (D-STAR) and they've gone to 10khz spacing. Some of the frequencies are within 10khz of frequencies allocated to analog repeaters. I would have to study the list to see if there are any with 10khz of each other in close proximity, but the fact that they've gone to 10khz spacing tells me that it probably is possible to do what I've described above.

An interesting side note is that it seems that the 2m coordinating body (TASMA) has embraced and being more proactive about finding ways for these two technologies to coexist. The 70cm coordinating body (SCRRBA) seems to be a lot less cooperative.

Reply With Quote
Old 02-24-2012, 11:58 AM
FatHam's Avatar
Senior Member
iTrader: (0)
Join Date: Apr 2011
Location: So Cal
Posts: 544
FatHam is on a distinguished road

And I gleaned some info from a TASMA guy this morning that SCRRBA isn't pro-actively dealing with the new narrow band formats AT ALL. They've got all kinds of band width that they're protecting so "Floyd" can have his three member "Sunday Night Net" once a week, even though the frequency isn't in use six days and twenty three hours out of the week.

He also pointed out that every Mormon Temple in So. Cal has an "emergency pair" just sitting there on a "closed" repeater, waiting for the call to go out that it's time to break out the rations in the garage.

He went on to say that it took going over TASMA's head to the FCC, complaining that new technologies involving narrower bandwidth are the future, yet the coordinators that they've assigned to ride heard on it in So. Cal were not recognizing the newer technologies. Perhaps it's time to start a letter writing campaign. Obviously it worked on TASMA.

Reply With Quote

Worldwide Radio Forum

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
can anyone please tell me what do to rob General CB Services Discussion 2 07-16-2011 06:08 PM
NXDN Digital Modulation C2 Digital Modes Discussions 4 06-11-2009 06:13 PM
The ARRL Letter Vol. 27, No. 8 February 29, 2008 AudioShockwav FCC & ARRL Activity 1 07-05-2008 09:36 AM
Marine Radio Rules Charger383 Scanning & Shortwave Listening 0 07-07-2002 07:12 PM
Frequencies Charger383 Scanning & Shortwave Listening 8 08-21-2001 06:44 PM

All times are GMT -7. The time now is 05:25 AM.

Powered by vBulletin®
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Optimization by vBSEO 3.6.0
Worldwide Radio Forum