repeater question

[topcop1833]

Anyone know if a P25 repeater will "passively" pass EAS encryption (or any other form for that matter)? Encryption is a new animal for us. We've been using it on simplex for a while and it has been working well. Our users can flip the knob and choose to talk clear or encrypted. We're looking at the ability to use a repeater from time to time. The majority of comms on this repeater are clear, however, we would like to go encrypted if needed. P25 would be cool, I'm ok with analog too. Are there any repeaters on the market that will do what i'm looking for, analog or P25?

[Tom in D.C.]

Do you mean "AES"?

[topcop1833]

face into keyboard....
yes, sorry bout that.

[judoka]

I would be surprised if any P25 repeater did anything other than passively pass the encryption. The repeater can work in one of three ways :
i) Take in the RF and repeat it (basically an analog repeater that passes the signal with sufficiently low distortion that the receiver can decode it).
ii) Demodulate the RF into a P25 bit-stream and then remodulate the bit-stream onto RF
iii) Demodulate the RF into a P25 bit-stream, apply forward error correction, re-encode the corrected bits, remodulate the bit-stream onto RF

In all cases, the actual voice content (encrypted or not) is untouched. Case iii) has the best performance because most of the errors on the uplink are removed before they get to the downlink but it will typically have a higher delay through the repeater. I know that the Tait TB9100 is transparent to encryption, I expect that the Motorola Quantar and Intellirepeater are the same. Anything built out of mobile radios with an analog path between them won't be transparent to encryption (and doesn't meet the P25 standards definition for compliance).

[judoka]

Just to clarify - there is a fourth way to build a repeater:
Take a P25 mobile radio which receives the P25 signal and converts it to audio on a speaker, take that audio and put it into the microphone input of a second mobile which transmits it as P25.

That method is not compliant with the P25 standards, has poor performance (high delay, increased audio distortion) and won't handle encryption transparently (each of the mobiles in the repeater has to contain the relevant encryption keys so that the receiver can decrypt and the transmitter can re-encrypt). It is a really bad idea to put your encryption keys into an insecure location (repeater site).

[topcop1833]

as for option four, we thought of that, and the audio was bad!!! as for the repeater site, its on our property, access control by our team. I guess we'll have to bite the bullet and get a p25 repeater.

[d119]

If you are looking to do this on the cheap, just get a used Quantar. It'll do everything you want.

[topcop1833]

d119, thats what I'm looking at doing... had our procurement folks look at if we can use ebay or not!

[d119]

Well you're not likely to get what you want from Motorola anymore, the Quantar station was canceled back in September, 2011.

So used is the only way to go really, and eBay is a good source.