HYDRA operating characteristics

[n4jri]

Been checking out what appear to be analog voice transmissions that I'll assume are actually EDACS/HYDRA. Using a combination of PSR500 and TRX-1.

Am finding that the same conversations quickly cycle through 3-5 frequencies, usually in the exact same order. There appear to be multiple users on what appear to be nearly identical sets of frequencies. Some users have the EDACS 'anti-scanner' beeps, but most don't.

Question 1 - When I hear pretty much the same frequencies sequenced over and over, does that tell me anything usable about those freqs' relationships as LCN's?

Question 2 - when reading a CC on the PSR500 I typically get EDW (EDACS wide?) C:xx (LCN#?) S:xx (Site #?) and both that I've read then have Hsa. Am assuming that the H is for HYDRA. Any idea what the other letters might mean?

Question 3 - sometimes certain frequencies drop in and out of the rotation. Is HYDRA set up to sense when another user has a CC or other traffic on one of its LCN's?

Question 4 - I don't pick up many input freqs, but have gotten a couple hits with PL 74.4 on what should be HYDRA inputs. Is there any content on the transmitted signal that would give my this tone reading with HYDRA?

I need to do some trunking analysis, but am new to anything other than Pro96com. For right now, I'm monitoring most of these things as conventional channels and would love to know what I can deduce from what I'm already getting.

73/Allen (N4JRI)

 

[Mattsenft]

While I don't know much about Hydra, EDACS is fairly easy and well documented. EDACS uses logical channel numbering for the voice and control channel. Based on the equipment you have, you could probably figure out the LCN order fairly quickly. Check out one of the trunking control channel decoders. Your PSR500 is already reporting the LCN of control channel and you can document that. Using a control channel decoder and scanning in conventional, you can easily determine the LCN for each frequency. With that info, you can program the system as an EDACS system in your scanner and search for talkgroups. I wouldn't read too much into the PL that you were seeing. It may just be audio on the channel falsing the decoder. Your best bet is to figure out the LCN order and monitor as an EDACS system. Your scanner will probably dump most of the beeps, and you will have some useful talkgroup info. By the way, in most normal EDACS systems the transmissions usually trunk through the LCNs in order unless someone has set up a special or random rotation. Hopefully this helps a little.

 

[n4jri]

Very helpful. In cases where I do get vessel talkgroups, only one or two are in that much use. The sequences of voice freqs used are highly consistent, although I have no way of knowing just how many vessels in the same area are using the same freqs. Even so, it's a place to start.

The next step is to figure out what hardware I need to connect my TRX-1's IF output to the computer.

In the meantime, it's still fun looking for stuff the old fashioned way

73/Allen (N4JRI)