The link repeaters have been around for decades. In fact, there used to be more of them. They are a backup system to microwaves. The forest net link repeats nearly all radio traffic in the forest (repeater or simplex) on the VHF forest net. Likewise with the Admin. Net (formally called the service net). Very useful for monitoring fires outside the local area. Quality is sometimes sketchy, but it's better than nothing.
Yes, they both use a PL of 103.5.
I was told by a friend who was a radio technician with Los Padres that they would go away at some point. However, they got new frequencies and new transmitters - so they will be around for a while I hope.
There used to be an air net link that repeated 168.625 - the air dispatch frequency at the time. You could hear aircraft and tanker bases all over the South Zone (now South Ops). Gone for years.
There was also a zone net link that was basically an intercom between all South Zone dispatchers. Also long gone.
Let me describe what UHF link frequencies do just to make sure there is accuracy on these pages. Remote base stations are regular base stations, just like a person would find in a simple radio system such as in a small town where the antenna on the roof allows the base station to hear all the radio traffic in town without the need for a repeater. Long ago, radio systems, especially those that don't cover a lot of area or rugged topography, operated on one simplex radio frequency. If a city was too large for all the mobile radios to be heard by the base station at the police station a base station was installed on top of a building or peak to take advantage of the increased coverage that a high place allows. Now, the base station and police station need to be linked together. Sometimes the solution was to do so using phone lines. A control console transmitted the voices onto a phone line, the phone line dumped the audio onto the remotely located base station, which then transmitted the audio on the radio frequency.
There was a disadvantage to this, the police station could hear all the cars, but the cars could not hear each other if they were located some distance apart. Also, if the area could not be covered by one remote base because some of your mobile units were located on the back side of a mountain ridge. The solution would seem to be another remote base and in some big cities that could be done. But, how about a large area where there weren't any phone lines close enough to hook into? The repeater was the solution as the mobile unit on the other side of the ridge could transmit to the repeater on one frequency and the repeater would then transmit back to the remote base near town on the other frequency. As the coverage area of radio systems expanded, the location of phone lines became a limiting factor. The solution was to replace the phone lines with radio links. That allowed that original remote base station to become the hub of a radio system, communicating to distant remote bases without the need for phone lines. As long as the remote base at the hub could "see" (or could "talk to") all the other radios in the system it could control the entire radio system.
In large cities radio frequencies began to become insufficient to cover the radio systems and all the links so some very high radio frequencies 1,0000 MHz and greater were installed to replace the link frequencies so free them up to build new radio systems. These so called "microwave" frequencies don't carry very far when used for mobiles and bases so they need their energy focused on a narrow path, thus carefully aimed dishes are used. Another factor with lower frequencies is they can be affected by weather and microwave not so much, so microwave provides the clearest signal possible. One disadvantage to microwave is that it requires a better quality power system and the older sites without commercial power aren't as dependable. Solar power and batteries are not really suited to microwave stations, although in the last ten years some microwave sites are being developed absent commerical power, although it is not the preferred solution.
Now a UHF link utilizes a beam antenna that focuses the signal into a narrow path, but nearly as narrow as microwave dishes do. Common terminology the line between the antennas at each end of a microwave path or UHF signal is a hop.
Now, how does all of this apply to the Los Padres National Forest? Well, in order to switch to microwave links a lot of money must be spent. On some National Forests in California it made little sense to build a federal system that duplicated a network the state had already installed. So the feds ended up leasing microwave circuits from the state. As money has become tighter, rather than replace more links with microwave, UHF links have replaced some of the microwave circuits or hops. UHF is also able to tolerate some intervening topography and vegetation better than microwave. The federal government has 406-420 MHz assigned to it and the feds use that band for links and for mobile radio communications in large cities. VHF is preferred for rural area communications and the feds have 162-174 MHz assigned to it.
The Supervisor's Office of the Los Padres National Forest is located in Goleta and dispatch is located In Santa Maria. One or both of these are linked with a single microwave hop. The hub remote base for the southern end of the Forest is on Santa Ynez Peak, which is not a repeater, but is a remote base. This remote base receives the output frequency of the repeaters and transmits the input frequency and the link frequency also passes on the subaudible tone (PL) selected by base consoles at fire stations, ranger stations, the Forest Supervisor's Office and dispatch. In this way the remote base is acting like a mobile or handheld radio located where the hub remote base is located and one repeater is selected for use at one time. If a scanner listener is somewhere near the hop of a UHF link the advantage is that the scanner will receive everything the remote base and dispatch is hearing. Thus, when I visit a family member in the Santa Barbara area I can hear all the south end repeaters, such as Frazier Peak, that I would not otherwise be able to hear from there.
I don't know how the repeaters on the Monterey Ranger District are linked to the southern end of the Forest. It could be on the state's microwave system on multiple hops or it could be many hops of UHF links. I suspect the first as the signal quality would be better over a number of microwave hops than of UHF hops. I don't know if there is a hub remote base on that district, but I think not.
It is not possible for the hobbyist to receive the microwave links. Hobby grade microwave receivers are not made and in addition one would have to have an antenna aligned to receive the vary narrow signal. This narrow signal does not refer to bandwidth, but to wavelength. The higher the frequency the shorter the wavelength.
I know this is long, but this is not a simple topic.
One last little bit of trivia, Santa Ynez can also transmit and receive on the repeater output frequency. If a mobile unit is within range of Santa Ynez and can't bring up a repeater they switch to simplex operation on the repeater output frequency, select Tone 8 (103.5) and speak with ranger stations, etc. without the use of a repeater. Thus you might hear "Los Padres" answering a mobile unit and not hear the mobile unit at all. However, if the UHF link for Santa Ynez is heard, the mobile unit's traffic will be heard.