Trying to understand USFS comms

[Kirk]

In my neverending quest for radio knowledge, I'm endeavoring to figure out how the USFS does its communications. I'm hoping some of us can share knowledge to figure out a little better how things are done.

My local forest is Las Padres, so all of my info is based on LPNF.

What I know:

The two main repeated systems are Forest Net and Service Net. They operate on multiple mountaintops with distinct PLs, as per the standard USFS tone plan. Dispatch center is in San Luis Obispo.

Most of the routine traffic, including units going in service, appears to occur on Service Net. Dispatches happen on Forest Net. I can't hear any distinct dispatch tones for particular units or stations, just a steady alert tone prior to the dispatch.

Obviously the tower at the dispatch center can't see all of the Forest Net and Service Net repeaters, so links are required. I haven't driven by there to see what kind of antennas they have, but I'm guessing there are microwave links (I've scanned UHF a bit, and haven't found anything. Might have just missed it, or they might be on microwave). I have monitored the inputs to the repeaters, and found something interesting.

I can hear the dispatch center on the input of Forest Net using several different tones for different peaks. I've therefore figured out that they're using a remote base somewhere that can hit all of the machines (at least all the ones to the South), and it appears as though they're selecting which tone to send by sending a short single DTMF digit with each keyup. This could be tone remote artifact I'm hearing, but it sure sounds like DTMF.

Interesting.

My questions are:

1. Is there any station alerting? Or do all of the stations simply monitor everything?

2. When I hear dispatch going out of service, how's that work? If there's a call in the middle of the night, who answers it? (note: This seems to occur more often when it's not fire season, but it still seems like someone must be on duty somewhere)

3. Am I right about the remote bases? The DTMF hilltop selection?

4. Are there additional remote bases for non-repeated channels? I notice a lot of listings for non-repeated channels, like Law Net, Admin Net, etc. They don't seem that useful if they're just car-to-car, but if remotes exist then they could be more useful.

Any info is appreciated!

 

[oregontreehugger]

Not sure about after-hours dispatch, but my guess is either CDF has an interagency dispatch center with USFS that can handle the radio traffic, or else there's really no USFS units on duty 24 hours a day during non-fire season. (Aside from law enforcement, and they probably have access to the local county sheriff freq. for after-hours.)

 

[digitaljim6]

1. There is no station alerting. Since USFS doesn't use volunteers, the responders are always expected to be monitoring the radio. The single tone prior to the dispatch is just an attention-getter.

2. In some areas, a manned station will telephone the dispatch center personnel on behalf of a radio user for after-hours service. In some areas, there are regional multi-agency centers which take care of after-hours service. If there is an after-hours incident, you may hear the normal dispatch center come back in service, then go out of service after the incident.

3. There are usually remoted control stations for each net, including LE. The links are mostly microwave now, although there was extensive use of 411/415 MHz for links in the past. Standard tone remote control signalling is used to select transmit CTCSS for mountaintop selection.

4. Law Net is repeated, and Admin Nets usually are. The most common "non-repeated" (simplex) frequencies would be Air Guard on 168.625 and Flight Following on 168.650. These are usually only deployed on a single site per forest because they are talking to aircraft and don't need ground coverage.

Law Net should be on 166.125 output with 164.625 input. There are some listings for Admin Nets for LPF on 170.475 and 172.350, but they are called tactical channels #3 and #2 in other listings. Don't know if there is any base station activity on them. If there is, it would probably be remote controlled via microwave or 411/415 MHz. If you never hear a base station, they are probably tactical rather than Admin.

 

[SCPD]

I'm a USFS retiree and can shed some light on your questions. I've also visited the "LP" dispatch center a couple of times, and spent about a month on this Forest on several assignments. When I get some time I will look at your questions and answer them from a former "insider" perspective.

 

[Kirk]

1. There is no station alerting. Since USFS doesn't use volunteers, the responders are always expected to be monitoring the radio. The single tone prior to the dispatch is just an attention-getter.

I knew they didn't have volunteers, but thought they might want stations that arn't getting toned out to be allowed to sleep through dispatches for other stations. I guess not.

2. In some areas, a manned station will telephone the dispatch center personnel on behalf of a radio user for after-hours service. In some areas, there are regional multi-agency centers which take care of after-hours service. If there is an after-hours incident, you may hear the normal dispatch center come back in service, then go out of service after the incident.

Ok, this makes sense. USFS LPF is co-located with CDF SLU, so perhaps the CDF dispatchers handle night calls. I'll have to leave a scanner on record overnight when fire season is over and see what I hear.

3. There are usually remoted control stations for each net, including LE. The links are mostly microwave now, although there was extensive use of 411/415 MHz for links in the past. Standard tone remote control signalling is used to select transmit CTCSS for mountaintop selection.

I'm pretty sure the 411/415 stuff has gone away here. I really should go drive by their tower and see what I can see. I'm not sure what the DTMF stuff is I'm hearing. Maybe they use non-Motorola (what I'm used to) tone remotes which sound different?

4. Law Net is repeated, and Admin Nets usually are. The most common "non-repeated" (simplex) frequencies would be Air Guard on 168.625 and Flight Following on 168.650. These are usually only deployed on a single site per forest because they are talking to aircraft and don't need ground coverage.

Law Net should be on 166.125 output with 164.625 input. There are some listings for Admin Nets for LPF on 170.475 and 172.350, but they are called tactical channels #3 and #2 in other listings. Don't know if there is any base station activity on them. If there is, it would probably be remote controlled via microwave or 411/415 MHz. If you never hear a base station, they are probably tactical rather than Admin.

I guess I'll do a bit more listening for law and admin nets. Thanks for the tips.

Exsmokey: Any input you can provide would be great, thanks!

 

[northzone]

Standard tone remote control signalling is used to select transmit CTCSS for mountaintop selection.

Actually, usually tone remote signalling is not used. What they do is send a single tone (sometimes called burst tone) up to the remote base to select the CTCSS, up to 16 different ones. A link channel, be it microwave, a phoneline, 70mz, or a 415mhz rf link will only pass the audio range (300-3,000 hz) not CTCSS. So they send a single tone out of the console which goes up the link into a panel at the remote base and is outputted as CTCSS to access the repeater. Normally you should not hear any of the single tone on the output because it is filtered in the conversion panel.

This was started when CDF converted from single tone to CTCSS repeater access and was such a good solution that the Forest Service soon started using the same system. I put many of these into service when CDF made the change years ago and it is still SOP today.

 

[MCIAD]

We work with LPF everyday, especially during the Summer Fire Season. I will try to shed some light on your questions.

There are no 24 hour Fire Stations/Engines on the forest. For the most part, most of the crews go home at 1800 hrs or so. With increased fire weather, that may get extended to 2000, and I have seen 2200, but the Feds have very strict work/rest rules that do not allow them to work after 2200 or so, depending on when they actually started the day, without getting mandated rest. Because of this, there is no need for individual station tones - everybody just maintains a state of Radio Stand-by.

The LPF and CDF-SLO are no longer co-located, haven't been now for a couple of years. Last I heard, and I can not confirm this right now (LPF is closed for the night), I think they are either operating out of Vandenberg Air Force Base, or the Santa Maria Airport - I have heard both. I will call them when I am next on duty and ask.

There are 2 "nets" that LPF uses, as stated already, the Forest Net and Service Net. Most of the emergency activity is off the Forest Net, including all of the initial dispatch fire responses. Service Net is used mostly for Law Enforcement, and support functions for the camp grounds and hiking trails. The Forest Net is built up quite a bit more than the Service Net, so you do hear some crossover traffic when the Service Net doesn't work (There are approx. 6 repeater sites for the Ventura County area for the Forest Net vs only 2 or 3 for the Service Net.)

Hope this helps - I'll post where LPF dispatch is on Tuesday, which is my next shift on-duty.

 

[Kirk]

I remember years ago when I was a search and rescue volunteer, we'd occasionally stage and run base camp out of Pozo Station. It seemed like it was well equipped for people to stay overnight (bunks, kitchen, etc), but I guess times change.

I remember when dispatch was in Goleta, and then it moved to CDF-SLO. I had no idea that they'd relocated again. I haven't worked in public safety for many years, so many of my contacts have dried up. Doing a bit of googling, I just discovered that they are indeed based out of Vandenberg now. http://www.fs.fed.us/r5/lospadres/fire/organization/

I'm guessing the remote base (and burst makes sense, but a fraction of a second of it is leaking into the remote base transmitter) for Forest Net to the South is either on Tepesquet or Santa Ynez. Pretty good signal here in southern SLO county.

I didn't think there were any other systems on air in the LPF other than Forest Net and Service Net. I have the mountaintops and tones, and have visited a few of the sites. Have also spent a few weekends at the Hi Mountain Lookout near Pozo for various activities (both amateur radio and SAR related), which is probably what sparked my interest in USFS years ago.

I'll throw a few of the law/admin channels into the scanner and let it log for a few days, but I suspect I won't hear much, if anything.

Thanks again for everyone's input.

 

[MCIAD]

Glad I could help - and now I do not have to call them.

 

[SCPD]

A Few More Things to Add

There have been some good answers to the original questions. I have a few things to add.

1. Is there any station alerting? Or do all of the stations simply monitor everything?

In addition Forest Fire Management Officers (FMO's) division chiefs (district FMO's), battallion chiefs, engine captains, crew superintendents, patrols and prevention units, law enforcement, District Rangers, and some recreation personnel carry pagers which are provided by vendors (mainly phone companies) which can be used to alert people who can't always be listening to the radio. People who are part of the "militia" (non-fire, non-law enforcement who are qualified in ICS positions and respond when needed) often have pagers also. These are visual and not voice as far as I know. Dispatches, the weather forecast, and extended attack fire situation information is put out to these pages and much of it can be retireived at the person's convenience. Some Forests in parts of the country still have some Motorola Mintors (sp?) which are used on the Forest Net and provide voice paging, but these are becoming rare because of their limitation.

2. When I hear dispatch going out of service, how's that work? If there's a call in the middle of the night, who answers it? (note: This seems to occur more often when it's not fire season, but it still seems like someone must be on duty somewhere)

Forest Service dispatch centers have a procedure where each center has a person on-call each night. These centers have to have someone on call 24/7/365 due to the use of personnel on non-fire incidents in the winter and for assignments to foreign countries. Examples are people sent to Australia when it is winter here, the Forest Service being assigned the lead in the space shuttle debris recovery, assignments of Type I and II incident management teams to the World Trade Center, hurricanes, all sorts of disasters, and to large planned events such as visiting heads of state, even communications personnel assigned to the last Democratic and Republican conventions to set up and maintain the National Incident Support Radio Cache for the event. Some Forests will have a dedicated phone line and a small console installed in the homes of dispatchers. Here on the Inyo the entire radio system uses 400 MHz links and people from Big Pine to Mammoth can operate the remote base on Silver Peak, east of Bishop, using UHF handhelds they can carry with them. Most of the after hours calls come from 911 centers where directories of home phone numbers for personnel are kept. I was on the Mono Sheriff's list for 18 years and got calls at night directly from them when the situation regarded any facility in the Forest's frontcountry (as opposed to backcountry or wilderness). Two years after I retired I got a call at 0200 requesting my help setting up a Search and Rescue command post. Needless to say during business hours the next day I made sure my name was purged from their lists, even though a letter requesting same had been written by the Inyo's dispatch when I retired.

Of the 18 National Forests in California (the Pacific Southwest Region or Region 5) 10 are not co-located with CDF. The Los Padres was co-located with the CDF San Luis Obispo Ranger Unit ECC from about 2000 up to a couple of years ago. I visited it when the radio techs were installing the microwave towers. There was talk of putting them in with the Vandenburg Air Force Base center. The 2004 R5 frequency directory shows the call sign for the Los Padres as "Vandenburg" but I don't know if that actually was implemented. The current directory chapter in the California Interagency Mobilization Plan shows the Los Padres dispatch center in Santa Maria on Mitchell Road. I'm not sure why their own internet site shows the dispatch center at Vandenburg. I would consider the Mobilization Plan to be the better source, however, they may have relocated since that was published or the internet site reflects infomation from a prior year (more likely).

I will continue in another post so I won't overload the server.

 

[MCIAD]

Forest Service dispatch centers have a procedure where each center has a person on-call each night. These centers have to have someone on call 24/7/365 due to the use of personnel on non-fire incidents in the winter and for assignments to foreign countries.

I should have been a little more specific . . .

LPF does have a person on call overnight from thier home. I do not know what kind of set-up they have now, but two years ago when we requested a response around 2 AM from them for a Brush Fire up in the Pinos District, the LPF dispatcher answered the phone at home, then had to travel into the LPF dispatch center. There was a delay of around 45 minutes for this to get accomplished, then a futther delay as the dispatcher then had to call out some of his crews from their homes. Overall it took a couple of hours to get the assistance, in their forest, that we needed.

 

[SCPD]

Overall it took a couple of hours to get the assistance, in their forest, that we needed.

That stinks. But ultimately it is Congress that is responsible. They have not given the Forest Service the ability to be more timely. Funding does not allow for mini consoles and dedicated phone lines to link them with the radio systems from dispatchers homes and does not allow for longer staffing patterns. Even when radios get installed in dispatcher's homes the pay rate is so low that turnover makes this difficult to keep maintained. The San Bernardino and Angeles are both 24 hour operations so it makes it easier. Even then it can take some time to get crews assembled and engines rolling.

It used to be that many fire stations had engine captains and/or crew sups living at a residence at the station and the Forest Service could require occupancy there in the job description. Then the Office of Personnel Management and the Office of Management and Budget, along with the IRS began to question agencies about the criteria for required occupancies because the employee could claim all or most of the quarters rental as a tax deduction and those agenices thought we were trying to get away with giving a benefit to employees that they didn't see as justified. Stand by used to be unpaid but then regulations did not allow that.

On real remote Forests, which California does not have except on the parts of the Klamath, the Modoc, and the Six Rivers, there isn't anywhere else to live but at the station and commuting is not an option. In those places night call outs work better, but then they don't have the need for them as much either.

All of this is why more and more agencies are combining efforts both in Federal interagency centers, Fed/State, and even Fed/State/Local centers. Colorado has a couple where Federal and State natural resource agencies, plus county fire and even sheriffs offices have pooled into some real interesting centers. It not only can, if worked right, provide additional hours of coverage, but result in better coordination as well.

I will get back to my answers to the original posts later. I have many outside chores to do right now to get ready for winter and I see it is spitting snow as I type this.

 

[SCPD]

3. Am I right about the remote bases? The DTMF hilltop selection?

The Los Padres National Forest (the "LP" in Forest Service lingo) uses microwave. Some Forests use only microwave, some use a combination of microwave and 400 MHz, and some use 400 MHz only. I'm not sure if the LP is the first or second, but I would lean towards microwave only. I think the hub of the system would be on Santa Ynez Peak, then that one would link to 3 to 4 others which would provide coverage by line of site to the remainder of the repeater sites, of which there are 14.



DTMF and burst tones are not used as these were phased out by the mid 1980's at the latest. All repeater selection uses CTCSS. There are 16 standard interagency tones in California used by all natural resource management agencies, except for the CA Dept. of Fish and Game. They changed their tone configuration about 5 years ago. Of the 16 tones 8 are standard nationwide. So in California if you have a repeater accessed by Tone 3 on a Forest Service system, a repeater accessed by Tone 3 on a BLM system, and a repeater accessed by Tone 3 on a CDF system, they all refer to the same tone frequency. You will hear radio traffic referring to these tones such as "Los Padres, Engine 51, Tone 2".

 

[SCPD]

continued

Here are the 14 repeaters on the LP's system:



North to South



Mt. Toro Tone 10 (107.2) Forest Net only

Anderson Peak Tone 13 (141.3) Forest Net only

Cone Peak Tone 8 (103.5) both nets

Calandra Tone 4 (136.5) both nets (shown on maps as Williams Hill)

Tassajera Peak Tone 9 (100.0) Forest Net only

Black Mtn. Tone 5 (146.2) both nets

Tepusquet Peak Tone 12 (127.3) Forest Net only

Plowshare Peak Tone 11 (114.8) both nets

Santa Ynez Peak Tone 10 (107.2) provides simplex access for the Service Net only.

La Cumbre Tone 3 (131.8) both nets

Mt. Abel Tone 7 (167.9) both nets

Frazier Tone 1 (110.9) both nets

Sisar Peak Tone 2 (123.0) both nets

Torrey Hill Tone 6 (156.7) both nets

Ranger district numbers for the LP are: 1 Monterey, 3 Santa Lucia, 4 Santa Barbara, 5 Ojai, and 7 Mt. Pinos. You wll hear these numbers being used in the call sign for each unit, such as Engine 41 (Santa Barbara), Patrol 52 (Ojai), etc.

 

[SCPD]

I'm having to break up my posts as I'm having a bit of a memory problem with my computer. Guess I will have to replace the chip.

4. Are there additional remote bases for non-repeated channels? I notice a lot of listings for non-repeated channels, like Law Net, Admin Net, etc. They don't seem that useful if they're just car-to-car, but if remotes exist then they could be more useful.

The two simplex frequencies for the LP are Channel 3 (170.475) and Channel 4 (172.350) and there are not any remote bases for these frequencies as far as I know. These channels are not just for the fire management function but all the other functions as well, those being recreation, wildlife, range management, watershed, surveying, archaeology, law enforcement, among a few others. Often it is difficult for field units to find a tactical frequency to use when there is a large fire on a Forest as they can't use the National Incident Radio Support Cache frequencies, most often referred to as NIFC frequencies, lest they interfere with units on the fire. Very few Forests have their own unique tactical frequencies and for the LP to have two suggests that these were originally authorized as a frequency pair for an Admin Net and then not used as such for some reason.

The Service Net frequencies the LP is using are one of about 6 or so used around the region for Service Nets which are utilized for Incident Command Post to Forest Dispatcher traffic only. Service traffic includes resource and material ordering and status. The use of Service nets is decliining as cell phones are used as much as possible for this function. The Service nets have been kept, but not upgraded, I presume for areas where cell phone coverage is not available or in case the phone system crashes. The Service net for the Angeles, San Bernardino, and Cleveland is all one frequency of 164.125 and there are very few repeaters. Putting rountine, day to day traffic on the service net is unusual and I'm surprised the LP does it.

Most Forests have a Forest Net, Admin Net, and Service Net. Many Forests are putting fire and law enforcement on Forest or Admin and then having the rest of the functions on the other net. Some call their nets Emergency or Fire and Admin or Forest. It all depends on the workload and resulting radio traffic unique to each Forest. The Angeles has their fire and law enforcement traffic on Forest Net and the remainder of the functions on Admin.

 

[SCPD]

When you mentioned one remote base having line of sight with all the repeaters on the south end, I would agree. I would imagine that the LP has one or two remote bases on the Monterey District, one on the Santa Lucia District, and one or two for the three southern Districts. I don't know the topography well enough to say and perhaps there are only two, one north and one south. I have heard the Forest simulcasting the weather and other announcements, sometimes making two announcements, one for the north and one for the south and calling it that on the radio so maybe there are only two microwave linked remote base/repeater combination sites. The one to the north is probably involves several paths or hops.

The Inyo National Forest resisted the installation of microwave for the backbone system for a few reasons. First only one remote base is needed and it is in the White Mountains east of Bishop. It is line of sight to all the other repeaters. So the microwave would only need to be one path. Second, the tower requirements for microwave are greater than those for 400 MHz, which only has to use some vertically polorized beams (Yagis) and a single pole will suffice. Third, when you have a 400 MHz linked system, UHF handhelds can be provided to dispatch personnel and they can work the entire system from their homes or cars and not have to drive to dispatch or have mini consoles installed in their homes. Additionally in buildings phone lines don't have to be run inside the wall or ceilings to link to a single base station as the UHF handhelds can be carried around the office and moved from desk to desk.

The push to convert to microwave has now started moving the other direction on many Forests. Microwave has greater power requirements and paying for commercial power is expensive. In some places State or private vendor (mostly phone companies) were utilized rather than building USFS microwave links. The lease costs for these arrangements are high enough that during budget cuts they are looked at as a significant liability. I've heard that during the narrowband conversion several Forests put 400 MHz links in to replace their microwave. The Sequoia comes to mind on this and in August I was monitoring quite a bit of traffic on that Forest from the Mojave area using a handheld with a 400 MHz frequency programmed in it. I like a system with 400 MHz links as it really provides each scanner with a remote base receiver, which microwave cannot. You just need to be located in the vertically polarized path, which is not all that narrow.


I hope this answers all your questions. I hope I did not "explain how to build a watch, when all you did was ask what time it was".

Anyone with questions about Federal natural resource agency communications should feel free to ask them as I'm fairly well versed on the organization and lingo of these agencies (U.S. Forest Service, National Park Service, Bureau of Land Management, U.S. Fish and Wildlife Service). I'm not all that well versed in the fifth federal wildland fire agency and a partner in NIFC (National Interagency Fire Center in Boise) which is the Bureau of Indian Affairs. I am well acquainted with ICS (Incident Command System) and having that knowledge allows understanding much of what is heard on the radio systems of these agencies. I even know a thing or two about CDF and DPR as I've worked with both of them and have many acquaintences still working for them.

 

[selgaran]

Thanks for posting all that...very interesting to read.

 

[SCPD]

Actually, usually tone remote signalling is not used. What they do is send a single tone (sometimes called burst tone) up to the remote base to select the CTCSS, up to 16 different ones. A link channel, be it microwave, a phoneline, 70mz, or a 415mhz rf link will only pass the audio range (300-3,000 hz) not CTCSS. So they send a single tone out of the console which goes up the link into a panel at the remote base and is outputted as CTCSS to access the repeater. Normally you should not hear any of the single tone on the output because it is filtered in the conversion panel.

Northzone is better versed in the workings of the dispatch consoles through the link to the remote base than I am. When I said that DTMF and burst tones were phased out in the mid 80's I meant that to apply to field radios: mobiles, handhelds, and non-linked base stations. Burst tone capability is built in to most amateur radios you can buy right now because these tones are still used in parts of Europe. As someone else on this thread indicated you can hear a short tone each time the a radio keys up the repeater. Burst tones are within the range of human hearing such as 1750 Hz and CTCSS (Continuous Tone Coded Sub-audible Squelch) is, as the name implies, below the range of human hearing (67 Hz to 254 Hz).

It should also be mentioned that often times a repeater is installed at the same location as the remote base. Whether the system is linked using 400 MHz or by microwave this can be true. On many Forests with microwave linking, the main backbone system of microwave linked remote bases does not have a repeater located with the remote base. In this case when a radio in the field is used simplex a tone to access the remote base must be used. This tone can be the same for all remote bases on the Forest or there is a unique tone for each remote base. Electronic sites not linked by microwave have the repeaters. Thus you will hear repeaters being used sometimes, allowing reception of both sides of the conversation. At other times the field radio is using simplex to talk to the dispatcher so you can only hear the mobile unit if you are within simplex range. The Angeles, Klamath, and Sequoia use this system. On some Forests you can only reach dispatch and linked base stations by using a repeater. Simplex traffic on the repeater output channel does not get carried through the links. In this way the dispatcher and Ranger Stations cannot hear field units using the output channel as a tactical and does not have to listen to field units talking with each other. Not having to listen to unit to unit traffic cuts down on the noise in the dispatch center and in Ranger Stations. The Shasta-Trinity National Forest (Shasta-T in USFS lingo), Mendocino, Modoc, Plumas, Tahoe, and Toiyabe in the Intermountain Region (the Toiyabe borders the Inyo, Stanislaus, Eldorado, Lake Tahoe Basin Management Unit, and Yosemite National Park) use this feature.

Regional areas of the Forest Service can be accessed via this link:

http://www.fs.fed.us/contactus/regions.shtml

When the Forest Service was using burst tones I found them annoying. All day long near my desk and out in the field I would hear the tone constantly, several hundred times a day anyway. When you are trying to keep one ear to the radio, even when it is turned down, and another ear to the visitor you are talking to, the constant beeping wears on you. In addition, when dispatch used a tone to alert everyone to an announcement or emergency dispatch, you didn't always distinquish it from the burst tones used to select repeaters.

When I mentioned that 10 Forest dispatch centers are not co-located with CDF I should mention that the dispatch center's call sign is normally the name of the Forest, e.g. "Angeles", "Los Padres", "Sierra", and where it is co-located with CDF it is the name of the city the dispatch center is located in, e.g. "Camino", "Grass Valley", "Yreka". The exceptions are the interagency dispatch center in Porterville, which dispatches for the Sequoia and for the BLM in central CA and has the callsign of "Porterville" and the dispatch center for the Cleveland National Forest which is co-located with the Monte Vista Ranger Unit but anwers to "Cleveland" on the Forest Service nets.

 

[digitaljim6]

Actually, usually tone remote signalling is not used. What they do is send a single tone (sometimes called burst tone) up to the remote base to select the CTCSS, up to 16 different ones. A link channel, be it microwave, a phoneline, 70mz, or a 415mhz rf link will only pass the audio range (300-3,000 hz) not CTCSS. So they send a single tone out of the console which goes up the link into a panel at the remote base and is outputted as CTCSS to access the repeater. Normally you should not hear any of the single tone on the output because it is filtered in the conversion panel.

This was started when CDF converted from single tone to CTCSS repeater access and was such a good solution that the Forest Service soon started using the same system. I put many of these into service when CDF made the change years ago and it is still SOP today.

Where the ECC and the control station were close by (one building to another), it was also used as a temporary method of gluing old burst tone consoles to new CTCSS transmitter equipment until the consoles could get replaced.

In that scenario, it is actually a terrible idea. It doubles the delay time between pushing the transmit button on the console and when the selected repeater actually starts transmitting. The "old" burst tone had to be decoded (hundreds of millisecs) before the CTCSS encoder even started encoding. Single-tone systems need a longer decode time to prevent falsing. Two advantages of standard tone remote systems (two tones) are quicker decode and better falsing immunity.

This delay caused a whole host of operational problems, from cutting off the first words of a dispatcher who is impatient (or forgets to wait) to causing other units to double with the dispatcher because the dispatchers can't key up faster and the other units think the dispatcher didn't hear them so they retransmit.

TCU got their new console equipment this season and those problems all went away - only because the extra delay is gone.

I believe the new CDF ECC equipment uses standard tone remote signalling. When you listen to a CDF ECC with a new console, you can hear it when the console automatically switches repeaters during a long multiple tone-out sequence.

By the way, digital carrier systems (like D3 or D4 on a DS1/T1) used on microwave can easily pass down to 50 Hz. I've sent CTCSS on them with no problem. Many simulcast systems which transmit CTCSS send it from a single source to each of their transmitter sites to keep the CTCSS from causing drop-out problems in the overlap areas. If each site had its own CTCSS encoder, the slight frequency differences of the tones eventually cause phase cancellation and the mobile receivers intermittently stop decoding. If memory serves, Sonoma County SO does centralized CTCSS encode on their 453 MHz simulcast channels.

 

[SCPD]

When listening to the USFS remember the R5 work channel of 164.150. This is used by field crews doing various types of work. Here on the Inyo it is used mainly by the construction, utility systems, and maintenance crews (roads, buildings, sewer, water). This is a relatively new frequency, having been assigned in the mid 1990's. This is not a tactical used for fire management.