ASTRO25 Simulcast capture window

[tone_P25]

Hi,

Does anyone know what the capture window time is on Motorola portables and mobiles (XTS2500, XTS300, APX6000, Spectra W3, APX6500)? I am looking setting the launch delay in the simulcast bases and am trying to determine the maximum delay of reflected signals that can be tolerated before they are interpreted as interference. Looking around the web I have seen some mention that Motorola radios operating on a 12.5kHz bandwidth have a capture window of 45us. Does this correlate with other users experiences? Would the timing be consistent with other vendor (Tait) products, i.e. is the only determining factor the bandwidth of the signal? What would the capture window be for a 25kHz service?

ASTROTAC's are configured so that the differential launch delay between them is minimized, GPS clocks, etc

Regards,

Tone

[jmfirefighter20]

In my system we are running 55us across the board out of our Quantars on narrowband P25. Don't forget that you need to compensate for the 5us of additional delay with EPIC V Quantar SCMs (that is, if you have an EPIC V mixed in with older EPICs, add 5us to the older stuff) Portables and mobiles that are tuned and aligned have no issues. We still have some trouble spots, but no system is 100%

[judoka]

Depends on the modulation used as well as channel bandwidth. If the transmissions use LSM, you will have a broader capture window.
I expect that the timing would be broadly consistent between vendors but the precise effect curve might differ slightly (ie if you check where the signal fails completely, the timing will be very similar, if you check bit-error-rates you might find some variations)

It is important to make sure that the portable/mobile is configured for the modulation that the base is using

[tone_P25]

Thanks for your response Joshua, we do have a mix of different EPIC cards (digital Qantar bases,upgraded EPIC cards in legacy analog Qantars) so that's good to know. Would different versions of the V.24 cards also introduce delay?

In regards to the 55uS if I understand correctly this is the launch delay setting in the Qantar itself. What I'm also wondering is what is the actual receive window time duration of the different portable/mobile radios (related to the eye pattern and assuming ASTRO25, phase1 - C4FM modulation) is, i.e. the maximum delayed signal the portable/mobile radio can receive before the signal is interpreted as Inter Symbol Interference?

When configuring the Simulcast Vote Group I have followed the process outlined in the ASTRO25 manual 'Motorola GPS Simulcast Installation Manual'. Delays are configured for differential Inbound delays (straight forward with the ASTRO-TAC 3000 Comparator with Ping) and the Outbound delays. Outbound are determined via Motolrola recommendations for their equipment and measuring ping times to the remote multiplexors from the local multiplexor.

ASTRO-TAC 3000 and Station Tx (Qantar) = 95ms <-recommended Motorola value
Station Buffer Allowance = 20ms <-recommended Motorola value
Delay through RAD Mux/Modem/E1 = ~77ms <- measured value
Total = 192ms

Regards,

Tone

[jmfirefighter20]

AFAIK, the version of the V.24 cards does not matter. It's the SCMs that have the timing differences.

I guess I misunderstood your question, and answered it as what seems to work the best around here for our particular system. You are correct, the 55uS I wrote is the launch delay in the Quantar itself.

[jmfirefighter20]

I want to add that I thought I saw somewhere that 90uS is about the max that a receiver can handle before it starts having issues as long as the strength differential between the two (or more) signals is great enough. http://www.simulcastsolutions.com has some information on simulcast design and implementation.