Joshua Tree Nat'l Park question

I just came back from a week at JTNP and, as usual, monitor the 171.675 freq for the Nat'l Park service.
I am able to hear 171.675 from just about anywhere in the park with varying levels of quality (at it's worst, it's still quite usable).

I switched to the repeater input (172.675 per the DB) and WOW!. Although it's listed as a "repeater input" in the DB, it sounds like the output of a repeater. Over in the Jumbo Rocks area, it has a full quieting signal. Same 146.2 PL.

Another thing I noticed listening to this is some of the units will have a short beep at the end of their transmission on 172.675. I don't think I've ever heard this on 171.675.

So it sounds like 171.675 and 172.675 are a simulcast of sorts.

Is there a link frequency I am missing or perhaps someone can explain how this works ?

Thanks.

Did you hear the other freq. 169.6500 simulcast ...?

It's fairly common in the park, and as far as I know in many national forests, to use direct (or talk around) mode. As long as units are in the same general area they can hear each other readily well, so they can use direct, bypassing the repeaters. JTNP is basically a big bowl, so a unit in the bottom can hear pretty much any unit 'on top.' I work out there and hear it used all the time, that's most likely what you're hearing.

Joshua Tree has a link on 417.575, and IIRC, transmissions are followed by a courtesy beep... Unfortunately, that's all I can hear in W.LA, so I have no idea how the VHF side hangs off that...

I logged 170.025 146.2 PL on my last trip to Arizona and it had the same dispatcher as 171.675. Perhaps another JTP freq?

Do you recall what types of transmissions were on that 170.025 frequency? Fire, Rangers, etc. It's not uncommon to have separate nets for various purposes. Also, any of what you guys hearing digital? From what I understand, they are planning on moving to digital sometime in the near future and are in the initial testing phases of it right now, most of the radio work is still analog, but there is some digital testing on the air once in a while.

avdrummerboy said:

Do you recall what types of transmissions were on that 170.025 frequency? Fire, Rangers, etc. It's not uncommon to have separate nets for various purposes. Also, any of what you guys hearing digital? From what I understand, they are planning on moving to digital sometime in the near future and are in the initial testing phases of it right now, most of the radio work is still analog, but there is some digital testing on the air once in a while.

Click to expand...

Almost everything I've heard on UHF was analog, however I did log some P25 last year with an NAC of 293

They split their 171.675 and 172.675 pair a year or two ago. Now these freqs plus others are repeater outputs. I don't have the input freq presently but I'm told it is a common freq shared amongst all of their sites with a different PL at each one. Also, I think 170.025 is the Chuckwalla rpt output.

Some additional info

Everything I heard was analog. I did hear mention of one unit calling another "on direct" several times.

On the 172.675 freq, on some units I heard a courtesy beep (which I didn't hear on the 171.675 freq.).

On a related note, I noticed just east of the Jumbo Rocks campground a hill with some 2 way antennas atop.
I don't know the name of the site but due to the full quieting of 172.675 in Jumbo Rocks, I wouldn't be surprised if that's where the repeater is.

Scotty - I didn't know about 169.650 but I'll plug that in for next time. We'll most likely head back there over New Years.

BCorbin - Thanks for the link freq. Any idea why this would be copy-able in LA ?

Thanks everyone for the great info.

166.275 is listed as an old input for the JTNP repeaters with various tones for various sites.

xilix said:

Everything I heard was analog. I did hear mention of one unit calling another "on direct" several times.

On the 172.675 freq, on some units I heard a courtesy beep (which I didn't hear on the 171.675 freq.).

On a related note, I noticed just east of the Jumbo Rocks campground a hill with some 2 way antennas atop.
I don't know the name of the site but due to the full quieting of 172.675 in Jumbo Rocks, I wouldn't be surprised if that's where the repeater is.

Scotty - I didn't know about 169.650 but I'll plug that in for next time. We'll most likely head back there over New Years.

BCorbin - Thanks for the link freq. Any idea why this would be copy-able in LA ?

Thanks everyone for the great info.

Click to expand...

I love JTP ...look forward to your report. The main repeater is on onyx.. I believe the tower your talking about is the freq I mentioned. Try to close call the tower area.

Reading data from our company radios, I get the following, only one that I have ever had work is Onyx and direct however, so not sure about the pairs, or tones.

Rx// Tx (dec PL/ enc PL) NAME

171.675/ 166.275 (146.2/ 141.3) JTNP ONYX
172.675/ 166.275 (146.2/ 127.3) JTNP BELLE
170.5125/ 166.275 (146.2/ 131.8) JTNP COPPER
169.650/ 166.275 (146.2/ 156.7) JTNP TRAM

Database shows input frequency as 172.675, however I cannot confirm nor deny this, it is entirely possible, as I mentioned above, they are in the process of moving to a digital system, perhaps part of that is shuffling of existing frequencies.

xilix said:

On a related note, I noticed just east of the Jumbo Rocks campground a hill with some 2 way antennas atop.
I don't know the name of the site but due to the full quieting of 172.675 in Jumbo Rocks, I wouldn't be surprised if that's where the repeater is.

Click to expand...

That site is Belle Mountain. JTNP does have a site up there.

I thought I remember reading somewhere that there are 6 repeater pairs at different places that use different tones for different uses (rangers, campgrounds, etc.)

xilix said:

BCorbin - Thanks for the link freq. Any idea why this would be copy-able in LA ?

Thanks everyone for the great info.

Click to expand...

My pleasure - glad I had it handy. My guess is, it's a combination of elevation and really lucky bounces off a fortuitously placed rock... 8*)

xilix said:

BCorbin - Thanks for the link freq. Any idea why this would be copy-able in LA ?

Click to expand...

Onyx Peak has a sliver of line-of-site coverage to LA... to Palos Verdes, to be precise. Light up PV with RF from Onyx, and it can be heard all over the place.

avdrummerboy said:

Reading data from our company radios, I get the following, only one that I have ever had work is Onyx and direct however, so not sure about the pairs, or tones.

Rx// Tx (dec PL/ enc PL) NAME

171.675/ 166.275 (146.2/ 141.3) JTNP ONYX
172.675/ 166.275 (146.2/ 127.3) JTNP BELLE
170.5125/ 166.275 (146.2/ 131.8) JTNP COPPER
169.650/ 166.275 (146.2/ 156.7) JTNP TRAM

Database shows input frequency as 172.675, however I cannot confirm nor deny this, it is entirely possible, as I mentioned above, they are in the process of moving to a digital system, perhaps part of that is shuffling of existing frequencies.

Click to expand...

Thanks, I got a close call hit a year ago with the 169.650 and asked RR people what it was and nobody confrmed it... I live in palm desert and the tram signal is a little scratchy... Onyx is super clear. Thanks for the updated info.

avdrummerboy said:

Reading data from our company radios, I get the following, only one that I have ever had work is Onyx and direct however, so not sure about the pairs, or tones.

Rx// Tx (dec PL/ enc PL) NAME

171.675/ 166.275 (146.2/ 141.3) JTNP ONYX
172.675/ 166.275 (146.2/ 127.3) JTNP BELLE
170.5125/ 166.275 (146.2/ 131.8) JTNP COPPER
169.650/ 166.275 (146.2/ 156.7) JTNP TRAM

Database shows input frequency as 172.675, however I cannot confirm nor deny this, it is entirely possible, as I mentioned above, they are in the process of moving to a digital system, perhaps part of that is shuffling of existing frequencies.

Click to expand...

kindly submit this info to the RR database...

Thanks folks for keeping track of this. I don't have a source of information for the radio system in this park.

Some National Parks and some National Forests are not using their repeater output frequencies for direct-simplex communications anymore. In the USFS they want all direct comms to be conducted on the Region Project Net, unless they are at the initial attack stage of a fire, which then gives them authorization for using the regional and NIFC tacticals.

The channel plan avdrummerboy posted is similar to that of Lassen, Sequoia-Kings (SEKI) and Grand Canyon National Parks. There is a single repeater input frequency and multiple repeater output frequencies. A voter is employed so that the ground units are not required to switch channels to find, by trial and error, the best repeater for their location. With multiple output frequencies the input frequency traffic is linked to each repeater and everyone hears everything at the park, no matter which repeater is being used. This is called a multicast system.

The frontcountry net of SEKI has used multicast system of two repeaters for more than 10 years now. They just added a third frontcountry repeater and now have a plan to multicast the backcountry net.

The only problem supporting that theory is the Onyx and Belle repeaters use the same output frequency. I don't know the location of the Belle repeater. Are the two separated enough to avoid interference from Onyx and they are able transmit from each simultaneously?

There is trend to establishing multicast nets like this on the larger national parks. That way everyone can hear everyone, no matter when they are. I believe that Great Smokey Mountains NP and Big Bend NP have had multicast systems for 10 or more years. I'm on the road so I don't have my Florida federal agency reference with me, but I seem to remember that the southern Florida parks, Everglades, Big Cypress, Biscayne and Dry Tortugas are all dispatched by Everglades and that Everglades has a multicast system, that might be shared with Big Cypress as well.

This makes sense. A couple years back NPS began taking parks served by multiple repeaters on a single Rx/Tx frequency pair, and gave each repeater its own frequency. Instead of having one channel and changing the repeater using operator selectable input tones, each repeater got its own frequency pair. Besides Joshua Tree, Point Reyes National Seashore is another place this happened, as well as Lassen Volcanic National Park.

I'd encourage anybody else who lives in range of some of the smaller National Parks around the state to search around 162-174 MHz, because this may have happened there as well. For instance, Death Valley seems like a likely candidate.

Edit: Exsmokey beat me to it, although not all parks simulcasting the same traffic through all the repeaters use a single repeater input frequency with receiver voting. Lassen for example appears to have a different input frequency for each repeater, although the traffic is still simulcast through all repeater outputs.