Angeles National Forest

[bcorbin]

For those of you who follow such things, it would appear that ANF has abandoned its links at 932 MHz

 

[JayMojave]

Hello Bcorbin: Wow I didn't even know they had a 932. link, just what 932 frequency is that? And what was it used for.

I am in the Mojave Desert on the North side of Angles National Forest, and can hear some of their radio transmissions. There use to be a UHF link some were near 415 MHz years ago that went down and was never reactivated.

Jay in the Mojave

 

[bcorbin]

Hello Bcorbin: Wow I didn't even know they had a 932. link, just what 932 frequency is that? And what was it used for.

I am in the Mojave Desert on the North side of Angles National Forest, and can hear some of their radio transmissions. There use to be a UHF link some were near 415 MHz years ago that went down and was never reactivated.

Jay in the Mojave

Hi Jay -

They had two point-to-point links -

932.6125 was used for Admin
932.6625 was used for Forest

I don't think I'd ever heard anything directly on the 941 MHz side of the links, but one could infer they were there from the interference they were at one time receiving from an ambulance company licensed on one of the same pairs. The signals at 932 were rather local to the SCV, so - presumably - they were feeds from Magic...

There seem to be rumblings of changes to at least a few forests (LPF has got the same output tone on all its repeaters now, CNF is rumored to be changing frequencies, ANF has revamped its links...) - there seems to be a move afoot to update/modernize many of the comms systems...

 

[SCPD]

This is the first time I've heard of the federal government using 900 MHz frequencies for linking. I was under the impression (incorrectly) that all linking was done in the 406-420 MHz band. That had been my experience during my career. Now that I'm aware of this I will do search additional spectrum when trying to find link frequencies.

I believe the Forest Service will making a lot of changes in frequency use in the near future. The NTIA (National Telecommunications and Information Administration) manual (commonly known as the "Redbook") has direction that all repeater input frequencies are to be in the range of 162.0500 to 166.4875 and repeater output in the range of 169.5125 to 173.9875. Single frequency assignments are to be in the range of 166.5000 to 169.5000. Federal agencies must comply with this direction by 1/1/19. A quick look at the RR database shows that present frequency use is far from these parameters. The Forest Service typically has repeater outputs in the 168.0000 to 173.0000 range and inputs in the 173.000 to 174.0000 range. Simplex frequency assignments had been made over the entire federal VHF band (162-174 MHz).

However, this is not entirely as straightforward as the above would indicate. The direction contains this statement: "Unpaired single frequency operations may be authorized using either of the paired frequencies, except pairs allotted AGA, if the requesting agency believes it to be a more effective use of the spectrum." I have no idea of how this can be interpreted and if remaining simplex assignments all over the entire 162-174 range will be allowed to continue. AGA stands for "All Government Agencies" assignments such as the federal agency common frequencies of 168.3500, 163.1000 and others.

These significant changes in frequency use began to be implemented in 2005 when narrowbanding became a requirement. The Redbook made major changes in the federal UHF band (406-420 MHz) as well. Repeater and link frequencies were spaced at 4 MHz with the output and downlink frequencies the higher of the two. The new direction has this at 9 MHz and output/downlink the lower of the two.

Most of the work done by the Forest Service since 2005 to comply with the Redbook has been on the UHF portion of their assignments. I picked up some information in the latter half of 2012 that a large effort would begin in the winter of 2012-2013 to bring VHF frequency use into compliance. At first I thought this meant that all repeaters not in compliance would just have their frequencies flipped so that the output was always the higher of the frequency pair. In reality the changes are to be much more significant.

I'm wondering if the observation that the 900 MHz links being discontinued have anything to do with this next round of changes.

 

[SCPD]

Hello Bcorbin: Wow I didn't even know they had a 932. link, just what 932 frequency is that? And what was it used for.

I am in the Mojave Desert on the North side of Angles National Forest, and can hear some of their radio transmissions. There use to be a UHF link some were near 415 MHz years ago that went down and was never reactivated.

Jay in the Mojave

The old 415 MHz link output frequencies you used to hear are now in the 406-410 MHz range and you should try doing some searches in that range to find those links again. Take a look at the NTIA manual on page 4-157 for a list of the new link pairs.

I wonder if 900 MHz links are still being used and just the frequencies have been changed? These are pretty easy to search as there are only 30 of them. A list is shown on page 4-167 of the manual.

Here is a link to the manual:

http://www.ntia.doc.gov/legacy/osmhome/redbook/Manual.pdf

 

[bcorbin]

Hey Smokey!

I've searched pretty carefully and systematically through the 932 and 941 bands over the last couple weeks, and - unless they've put up one heck of a directional antenna - they're no longer there.

I was going to mention the NTIA bandplan, but SoCal is such a mess, I'm not totally convinced it will ever be completely NTIA compliant. Way too much going on. There really aren't any signs that the FBI or DEA are in any big hurry to re-configure their systems, and until/unless they do, it's going to be hard to get anyone else moved where they're 'supposed' to be...

 

[bcorbin]

I was going to mention the NTIA bandplan, but SoCal is such a mess, I'm not totally convinced it will ever be completely NTIA compliant. Way too much going on. There really aren't any signs that the FBI or DEA are in any big hurry to re-configure their systems, and until/unless they do, it's going to be hard to get anyone else moved where they're 'supposed' to be...

Put another way - 2019 is an eternity away, in terms of how rapidly communications technology is evolving.

Given what it would take to coordinate a new band plan for the LA Basin (hell - given what it would take to get all the parties to sit around a table to talk about it), it's going to be a lot easier for everyone involved to just hunker in place (with small ad hoc changes) until there's either an obvious technological solution (say, ubiquitous high-end broadband) or the force of an imminent intractable deadline.

I suspect that the changes that are being made within the USFS are being driven, not so much by the need for compliance here in LA, but rather to sort of harmonize procurement/maintenance throughout the system - it's a lot easier to maintain systems when they all work in more or less the same way... exceptions are expensive...