Kern County Fire Extenders?

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LZJSR

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I have heard KCFD Battalion 5 ask several units on scene of calls, over the past few weeks, to turn on their extenders. Does anyone know what frequency/channel is used for the extenders, and any other details about the extenders?
 

karldotcom

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well, googling the term comes up with this...but I don't know how old that data is:

EXTENDER Pyramid Mobile Extender, 173.2250, 167.9
 

zerg901

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Usually the extender freqs are listed in the FCC ULS. Look for 1, 2, 4, or 5 watt mobiles. The extenders themselves carry a MO3 designation. Licensing seems to vary - sometimes the portable freq and the MO3 freq are listed - sometimes just 1 of them is listed. The exact configuration can be tough to figure out.

Kern County FD might use the North input freq as the extender freq in the South area - the East input freq as the extender freq in the West area - ie etc approx

Some agencies use business band low power freqs - like 151.88 and 151.82 etc

Some agencies also use freqs near 173 Mhz and 170 mhz (typically or formerly known as "wireless microphone" channels.)

Sometimes 2 bands are used - VHF and UHF - or UHF and 800/700 - or 700/800 and VHF - ie etc approx
 
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Eng74

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The extenteders are on the engines. We will have one of the engines turn its extender in a spotty coverage area, There are some in Battalion 5 near Ventura County in the Mountains up there. The simple way it kinda makes the engine a repeater.
 

LZJSR

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So do the units switch their handheld/portable to the extender frequency, and the engine has a repeater/second radio that receive the handheld transmit frequency, and then rebroadcasts it over the normal command channel from a second radio? Or do they have a separate handheld on a different band (i.e. UHF) that they use as the radio when they want to use the extender? Do you know the frequency that is used for the extender input/output? Thanks in advance.
 

Eng74

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Same radios are used all we do is turn on the switch in the cab.When they put them in I was told is was same or similar to what CHP has. No channel changes HT's can stay on in your case Kern 3 but it works on all of the Kern channels but not the Tacs since they are line of sight.
 

zerg901

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Eng74 - can you talk to the dispatcher when that extender is turned on? Or can you just talk to other nearby units who are working at the same incident?
 

Eng74

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Eng74 - can you talk to the dispatcher when that extender is turned on? Or can you just talk to other nearby units who are working at the same incident?
Yes we can talk to ECC or the Battalion Chief on the channel in Batt 5 would be Kern 3 or Kern 2 deppending.
 

zerg901

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I guess the next question should be - when a extender is turned on, can scannerists hear the extender as well as the scannerists can hear the dispatcher? Another good question would be - can HT74 talk countywide (or areawide) when using the extender?

The clues I have are -
1. HT does not have to change channels when the extender is turned on
2. Extender is turned on by flipping a switch in the cab of the Engine
3. HTs can talk to dispatcher and BC (and other units I imagine) when using the extender
4. extender is only used in weak coverage areas

The Radio Reference database shows Kern FD Channel 2 as 155.88R 158.94in - therefore the HTs that are using KFD Ch2 must be transmitting on 158.94, and receiving on 155.88 - whether or not a extender is turned on. Presumbably.

I have 2 guesses at this point.

A. The extender is actually functioning as a temporary remote receiver site - in the Ch2 case, it would receive on 158.94 - and possibly transmit on some other freq back to the infrastructure - maybe a UHF freq. The signal would then be fed into the voter system like any other signal on 158.94. Do the trucks still have UHF antennas on the rigs/cabs?

B. The other alternative (in the KFD Ch2 case) might be that the extender receives on 158.94 and retransmits on 155.88 - but the dispatcher listens in via a mountain top receiver on 155.88.

Dont ya just love a good mystery?
 

SCPD

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The way they work in Mono County where there is one frequency for the Sheriff's office and one for the volunteer fire department and county paramedics. Both of these are UHF frequencies. When a paramedic turns on the extender it receives and transmits on one of those UHF frequencies. When they key up their handhelds the mobile in the ambulance transmits on the input frequency of the channel they are on, usually county fire dispatch. When the repeater transmits the reply the mobile then transmits the signal on the same UHF frequency.

The same is true for the sheriff's deputies. The paramedics have a choice of what frequency they keep the mobile on and what frequency they will be able to work remotely. They usually leave it on county fire dispatch to be able to listen to additional calls and to keep the dispatcher appraised of their status. They could also link up to the paramedic-hospital net if they were in a marginal area for hand held radios and their patient is some distance from the ambulance. They can put their mobile on a simplex frequency and the extender would then be able to transmit and receive on it. They can also put their mobile on sheriff's department frequencies and communicate with deputies who are accessing the sheriff's office frequency using their extender frequency, which as I mentioned is different from the fire/paramedic extender frequency.
 

f40ph

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Kern Co portables have an extender freq on Ch16 (last channel in group 1 of the radio). My understanding is the crew turns on the pyramid mobile extender in the Engine (maybe it's always on?) Then switches the portable to Group 1, Ch 16. This will "extend" via 173.225 whatever channel the engine radio is on. This frequency is only programmed in the portable and not the vehicle mobile radio which tells me they must switch channels on the portable to take advantage of the extender "repeater" yet may switch back to the standard repeater pair at any given time.
 

zerg901

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f40ph - that would make lots of sense. 173.225 from portable to extender - and 173.225 from extender to portable. The extender probably has a sensing mechanism that gives priority to messages from the portables versus messages from the extender.
 

inigo88

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f40ph - that would make lots of sense. 173.225 from portable to extender - and 173.225 from extender to portable. The extender probably has a sensing mechanism that gives priority to messages from the portables versus messages from the extender.
I agree, thank you f40ph!!! For CHP it's a lot more straightforward because the portables are on a separate radio system (VHF or 700 MHz) from the mobiles (lowband). But with agencies like Kern County FD that have the same channels in the portables and the mobiles, people have to remember that the vehicle can't just "listen on the input frequency and retransmit", because the transmission from the extender would occur on that same input frequency and cover the portable's traffic unless there was some sort of significant built in delay. This is why you always see extenders on their own discreet frequency.

As far as the sensing mechanism to give priority to the portables instead of the extender, this is done through "lookback" scanning whenever the extender is transmitting (just like priority scan on most scanners). If you ever monitor CHP's Pyramid Extenders, whenever they're transmitting traffic being received by the car's mobile radio, you'll hear the audio clip briefly about once every second. This is because the extender has stopped transmitting briefly to see if the portable is trying to get through on the same frequency - just like your scanner in priority scan checking the priority channel every second while another channel is being received. This is why the beginning of CHP officer's transmissions are occasionally clipped, because they keyed up their portable and started talking before the extender had time to make that once per second "lookback" check (if it was already busy transmitting traffic from dispatch or another unit).

My own techno-geek question about the Pyramid Extenders which I've had for some time now, is how they know to shut themselves off when a new unit with it's extender turned on arrives at the scene. Apparently if there are multiple vehicles in the same place with all their extenders on, each new vehicle that arrives takes over as the primary extender and tells the others already there to shut themselves down (to prevent all the extenders from transmitting at the same time and covering eachother). According to the CHP radio historical web page, when this happens officers will usually have to turn the extenders off and then back on to reset them for normal operation. I'm curious about how this shutdown command from the arriving extender is actually accomplished - whether it pings the others with a subaudible tone or what. They seem to follow such simple operation, that whatever their solution must have been pretty clever: :)
 

zerg901

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inigo 88 - I once saw an (online) article about the CHP extenders that had lots of details - maybe 6 pages long - you might try to find that.

Re the shutdown command - I think it works this way -

Unit A arrives - sends out ping - listens for reply ping - hears no reply ping - takes #1 status

Unit B arrives - sends out ping - Unit A sends ping as #1 - Unit A will now stop sending pings - Unit B now knows that it is number 2 at scene

Unit C arrives - sends out ping - Unit B sends ping saying that Unit B is #2 at scene - Units B will now stop sending pings - Unit C knows that it is number 3 at scene

I guess that if Unit A leaves the scene, it sends a bye bye ping which maybe bumps everyone else up one position on the totem pole

(I might be way off on this - I am going from memory - I just wanted to reply before I forgot that the question had been asked)

(I think I remember where I have that CHP article squirreled away - let me check)
 
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zerg901

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I found it - APCO Bulletin June 1982

4 paragraphs to type up - here we go

(actually - I dont see Pyramid mentioned here - maybe this info is way out of date)

As soon as a system is turned ON, it does 2 things. First, the repeater transmits a one second 847.5 Hz tone burst which will be recieved by other enabled repeaters in the vicinity. Receipt of the tone will cause those repeaters to change their delay states. Second, it assumes a state of readiness to instantly repeat any traffic accepted by its 150 Mhz and 42 Mhz receivers. That state of readiness is referred to as "delay state zero". The eight delay states are timed in increments of 400 milliseconds, as shown below.

Delay State 7 - milliseconds to reach delay state zero - 2800
6 - 2400
5 - 2000
4 - 1600
3 - 1200
2 - 800
1 - 400
0 - 0

A system will wait 400 milliseconds before stepping down to a shorter delay state after its receivers have sensed acceptable traffic that requires repeating, but is NOT being repeated. Note : A system steps up to a longer delay state only on receipt of the priority tone from the last system activated. That tone is generated only at the time the repeater is turned on by the officer before leaving the vehicle.
 
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zerg901

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Continuing with info from APCO Bulletin June 1982

Figure 7 - Car 4 - delay state zero (0 delay) - Car 3 - delay state one (400 ms delay) - Car 2 - delay state 2 (800 ms delay) - Car 1 - delay state 3 (1200 ms delay)


The cars are numbered in sequence on their arrival. Car 1 arrived first, and therefore its system was turned on first. As each car's repeater was turned ON, it established its own system in delay state zero and transmitted an audible tone to notify all other systems to step up to the next highest delay state. All of the systems will detect the prescence of traffic requiring repeat, but only system 4 will repeat instantly. If 4 does not repeat, 3 will wait 400 milliseconds, step down to delay state zero and repeat the traffic.

When a patrol unit leaves the scene, its repeater must be turned off. The systems remaining will, after detecting acceptable traffic, step down to the proper delay states until one of them is again in delay state zero.

(Something tells me that this is all absolutely the opposite of what I had guessed earlier)
 
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zerg901

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Continuing with APCO Bulletin June 1982 info

If the MICOR microphone is used immediately after the officer turns on his repeater, the system will automatically step to delay state 4. It will then take 1.5 to 2 seconds after the next portable transmission for the system to drop to delay state zero. To avoid this delay after using the MICOR microphone, the repeater can be recycled OFF/ON by the officer before leaving the vehicle.

It is essential that the repeater be turned on just before the officer exits the vehicle, and turned off when the officer leaves the scene. Repeaters must not be left on when not required. Leaving a repeater on needlessly will cause unnecessary delays for other officers, noise and garbled traffic reception at dispatch, and may cause uncontrolled misdirection of trffic to the wrong officers and dispatchers.
 

inigo88

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Fascinating read, great find Zerg, and thank you so much for typing it up!!! I've actually heard that 800 Hz audible tone before on the CHP VHF extender frequency and wondered whether it was related to the on-scene cueing. I was also curious what the ramifications of cruising around with the extender left on would be, since CHP tends to forget to turn them off a lot. This answered that question:

It is essential that the repeater be turned on just before the officer exits the vehicle, and turned off when the officer leaves the scene. Repeaters must not be left on when not required. Leaving a repeater on needlessly will cause unnecessary delays for other officers, noise and garbled traffic reception at dispatch, and may cause uncontrolled misdirection of trffic to the wrong officers and dispatchers.
I know this is a Kern County Fire thread and I'm talking about CHP, but since both departments use Pyramid VHF mobile extenders, the operation should be the same for both. Thanks again, I love learning new stuff like this. And as I suspected, for 1982 technology that was pretty clever. :)
 

ramal121

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Pyramid has a clever protocol for multiple units at a scene, but it is not 100% infallible.

This is from the service manual:

When the SVR-200 is first activated, it will transmit a short “lock tone” that alerts the user that the system is
functioning. It will then assume the priority status and be ready to repeat any base-to-portable or portable-to-base
transmissions. If another unit arrives on scene and is activated, it too will transmit the “lock tone”; when the first
SVR-200 detects the lock tone from the second unit, it will increment a “priority counter” and will no longer repeat
any transmissions. The recently arrived unit will be the priority repeater, and the first unit will be 1 count away from
priority. This process will continue for each unit that arrives at the site, creating a priority hierarchy for up to 256
vehicles, each with a unique count and only one unit at priority status. The SVR-200 will not transmit it’s lock tone
if the radio channel is busy when first enabled. It will wait in non-priority status until all transmissions cease, then
send its lock tone and become the priority unit.
Even though the other SVR-200s are not at priority status, they will continue to monitor the channel for activity.
If the priority unit were to leave the scene or become disabled, the other units will detect the condition to repeat
and determine that there is no priority unit repeating the transmission. They will then begin to decrement their
priority counters until one of them reaches the priority status and begins repeating the transmission. Since the
SVR-200s are all at different counts, only one will reach priority status and begin transmitting. The other units will
sense the new priority repeater and cease counting down, preserving the priority hierarchy.
If another unit were to arrive from a different scene and it is still the active priority, there will be two active
repeaters on the air when a condition to repeat exists. When one of the SVR-200s unkeys to check for handheld
activity, it will detect the presence of the other active SVR-200 and increment it’s priority counter and cease
transmission. This is the self clearing mode to prevent radio collisions.
If the handheld operator is out of the vehicle and their partner still in the vehicle were to key the mobile radio
using the local mic, the SVR-200 will detect the local PTT and repeat the transmission to the other handhelds so
that both sides of the conversation will be heard by everyone on the link. The local mic repeat function can be
enabled/disabled via the PC software.
The SVR-200 also has a local receive audio speaker jack that enables the person in the vehicle to monitor
portable-to-base transmissions that are being repeated through the mobile.
If the users wish to communicate portable-to-portable without accessing the mobile repeater, they may transmit
on the same frequency without CTCSS (or a different CTCSS); the SVR-200 only responds to carrier and proper
tone from the handhelds.
 
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