4 Mike Alpha (USFS Helo)

[cjrjr507]

Hi all

Just thought I would let you all know that forest service helo (4 Mike Alpha) is headed for Grangeville, Id from Libby, MT airport about 10 minutes ago, give or take. Heard it on 415.525

 

[ecps92]

415.5250 is likely a Downlink from a Remote site for one of the VHF sites.
Could be an AM/Aircraft link or an FM/Air-Ground or Repeater link.

See if you can find the other pair to it.
Also make not of the CTCSS being used

Hi all

Just thought I would let you all know that forest service helo (4 Mike Alpha) is headed for Grangeville, Id from Libby, MT airport about 10 minutes ago, give or take. Heard it on 415.525

 

[cjrjr507]

415.525 mhz usfs Kootenai UHF link repeater

415.5250 is likely a Downlink from a Remote site for one of the VHF sites.
Could be an AM/Aircraft link or an FM/Air-Ground or Repeater link.

See if you can find the other pair to it.
Also make not of the CTCSS being used

Hi ecps92

yeah, that frequency is an usfs uhf repeater link. input is 406.525 with lots of different CT tones.
Aircraft use it a lot for contacting dispatch. The other one they use is 415.225 mhz with 406.225 as input.166.9000 is Kootenai A/G south though. They have a fire somewhere south of Libby, mt. There is a couple of air tankers on it. And some helo's Oh and 4 Mike Alpha is back flying around.

 

[SCPD]

Hi ecps92

yeah, that frequency is an usfs uhf repeater link. input is 406.525 with lots of different CT tones.
Aircraft use it a lot for contacting dispatch. The other one they use is 415.225 mhz with 406.225 as input.166.9000 is Kootenai A/G south though. They have a fire somewhere south of Libby, mt. There is a couple of air tankers on it. And some helo's Oh and 4 Mike Alpha is back flying around.

Are you close enough to hear the uplink? The reason I ask is the downlink should be the lower of the pair, thus 406.525 should be the downlink and 415.525 should be the uplink.

 

[ecps92]

I thought they always used One PL Tone for each link. [maybe eXSmokey can validate that]

The multiple PL's is odd, unless it's passing the tone of the VHF

Hi ecps92

yeah, that frequency is an usfs uhf repeater link. input is 406.525 with lots of different CT tones.
Aircraft use it a lot for contacting dispatch. The other one they use is 415.225 mhz with 406.225 as input.166.9000 is Kootenai A/G south though. They have a fire somewhere south of Libby, mt. There is a couple of air tankers on it. And some helo's Oh and 4 Mike Alpha is back flying around.

 

[thewenk]

I thought they always used One PL Tone for each link. [maybe eXSmokey can validate that]

The multiple PL's is odd, unless it's passing the tone of the VHF

From what I've seen the vhf PL tones get passed through to the UHF link.

The multiple PLs come from each vhf repeater having it's own tone. So several different tones can show up on the same UHF link frequency, depending on which vhf repeater is being used, and there can be a number of different repeaters depending on the size of the Forest or BLM net.

For example
Eastern Idaho Interagency Fire Center Scanner Frequencies and Radio Frequency Reference

Dave

 

[SCPD]

I thought they always used One PL Tone for each link. [maybe eXSmokey can validate that]

The multiple PL's is odd, unless it's passing the tone of the VHF

The tone is passed along so that the dispatcher's screen identifies the repeater being used. Most Forest Service radio systems have a hub remote base linked to the dispatch center by UHF. The remote base can "see" all the repeaters on the system. The only way to identify the repeater in use is to have it transmit the input tone on the output. This tone is then carried on the downlink.

Some National Forests use microwave for links or a combination of it and UHF. A few remote bases linked by microwave are placed in key locations. These systems are able to distinguish what remote base is receiving a field signal the best as voters are typically used. Some systems use UHF links between the VHF repeaters and the remote bases. In this case the link carries the tone of the repeater.

Some NF's use a different tone on the output than on the input. Why this is done is a question I cannot answer. The function of the tones remains the same, however.

 

[thewenk]

The tone is passed along so that the dispatcher's screen identifies the repeater being used. Most Forest Service radio systems have a hub remote base linked to the dispatch center by UHF. The remote base can "see" all the repeaters on the system. The only way to identify the repeater in use is to have it transmit the input tone on the output. This tone is then carried on the downlink.

Some National Forests use microwave for links or a combination of it and UHF. A few remote bases linked by microwave are placed in key locations. These systems are able to distinguish what remote base is receiving a field signal the best as voters are typically used. Some systems use UHF links between the VHF repeaters and the remote bases. In this case the link carries the tone of the repeater.

Some NF's use a different tone on the output than on the input. Why this is done is a question I cannot answer. The function of the tones remains the same, however.

Thanks for the explanation.

Dave