Here on the bench my co-worker and I have set up a VHF conventional base station with a UHF RA/RT 'hot link' configuration (all T5365A Quantars with version 13.xx firmware).
Both UHF stations are keyed continuously simulating a wireline, configured for analog wideband 4-wire full duplex, with ASTRO modem data running over the link. The DIU3000 is connected to a UHF station at the 'low' end, multiple parallel consoles are connected to the DIU via TRC. The other UHF station is connected to the main VHF station at the 'high' end. The equipment has been configured as per Motorola FTR recommendations via a short phone call but did not receive more specific, direct support (that costs some serious bucks even for doing it over the phone).
It has been working pretty good, although every week or so the ASTRO modem connection (not the RF link itself) will drop and not recover unless I cycle power on the UHF station at the high end. Any ideas? The UHF stations are both on dummy loads separated about 5 feet from each other, FM deviation is about 3 KHz and RSSI shows good on both ends.
This equipment is slated to replace an existing Micor guard-tone keyed TRC UHF link that has been in place for over 25 years. There is plenty of signal at both ends that has never noticeably faded and is multipath-free.
I was wondering if any of you may have come across a setup similar to or the same as this configuration, and what luck have you had with it? Did you have to do anything special to get it to work reliably? We would like to put this thing into service and have some sense of comfort knowing it will work reliably…
ASTRO modem over hot-keyed UHF link?
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ASTRO modem over hot-keyed UHF link?
Casey KJ7XE
Is this system going to be P25 digital or mixed digital/analog? If it's analog only, you may not even need the DIU.
With Astro modems on mixed digital/analog systems, analog voice is sent over the line in analog--it's not digitized and modulated by the modems. The modems essentially disconnect themselves for the duration of an analog transmission to let the analog voice have the line. I've heard that if an analog transmission is long enough (maybe a minute or two), the modems loose their clock, and take about 30 seconds to re-sync once the analog transmission ends. During this re-sync, no P25 digital voice can pass over the wireline.
I've worked with several P25 digital conventional VHF systems linked/controlled via UHF, but never one that required the UHF link to be on the air at all times... Just curious, but why does the UHF need to be on all the time? Is your VHF base full duplex on a frequency pair?
For digital operation, since it sounds like the VHF and UHF Quantars on the hill are in the same rack, you could try and replace the Astro modems with TTN4010 V.24 cards, and see if you have better luck with that. For analog-only operation, I'm not sure why you would need the Astro modems at all, as a simple PTT/audio/ground connection should work.
With Astro modems on mixed digital/analog systems, analog voice is sent over the line in analog--it's not digitized and modulated by the modems. The modems essentially disconnect themselves for the duration of an analog transmission to let the analog voice have the line. I've heard that if an analog transmission is long enough (maybe a minute or two), the modems loose their clock, and take about 30 seconds to re-sync once the analog transmission ends. During this re-sync, no P25 digital voice can pass over the wireline.
I've worked with several P25 digital conventional VHF systems linked/controlled via UHF, but never one that required the UHF link to be on the air at all times... Just curious, but why does the UHF need to be on all the time? Is your VHF base full duplex on a frequency pair?
For digital operation, since it sounds like the VHF and UHF Quantars on the hill are in the same rack, you could try and replace the Astro modems with TTN4010 V.24 cards, and see if you have better luck with that. For analog-only operation, I'm not sure why you would need the Astro modems at all, as a simple PTT/audio/ground connection should work.
Unless the DIU is connected to a Centracom console ACIM for full Astro signalling capability or you are planning on encryption of the P25 traffic and want the link secure as well, I would consider relocating the DIU to the 'high' end. Then all you would need to pass up the link would be analog audio from the tone remote consoles.
If you need the DIU to be at the console location for either of those reasons, you might try fiddling with the analog and digital link check parameters. Also, as 515 indicated, there is a setting for how long the station will let the line stay analog before the modems attempt to re-sync. You should check that setting.
If you need the DIU to be at the console location for either of those reasons, you might try fiddling with the analog and digital link check parameters. Also, as 515 indicated, there is a setting for how long the station will let the line stay analog before the modems attempt to re-sync. You should check that setting.
The system is 'mixed mode' P25/analog conventional. The VHF station is on a mountaintop that communicates with units in direct range and through 9 repeaters throughout the area.
The purpose of going with such a link as opposed to one of the common options (or putting the DIU at the high end) is to preserve DES-OFB encryption from the VHF station all the way down the link to the DIU to meet security requirements for encrypted radio traffic, the ability for ACIM data, and to allow for IVD capability for data and OTAR at a later date.
The FTR's recommendation was to run ASTRO modems over either a microwave circuit or a UHF link to/from the mountaintop. Since we already had the equipment to do a UHF link, we went ahead and built it up.
I was told that the 'digital link check' field should be disabled for this application, and since ASTRO modems are used, the 'analog link check' feature is not used.
I see the 'analog call timeout' setting under the Base Station Parameters in the DIU CSS, i'll mess with it and see how it behaves with the link.
The purpose of going with such a link as opposed to one of the common options (or putting the DIU at the high end) is to preserve DES-OFB encryption from the VHF station all the way down the link to the DIU to meet security requirements for encrypted radio traffic, the ability for ACIM data, and to allow for IVD capability for data and OTAR at a later date.
The FTR's recommendation was to run ASTRO modems over either a microwave circuit or a UHF link to/from the mountaintop. Since we already had the equipment to do a UHF link, we went ahead and built it up.
I was told that the 'digital link check' field should be disabled for this application, and since ASTRO modems are used, the 'analog link check' feature is not used.
I see the 'analog call timeout' setting under the Base Station Parameters in the DIU CSS, i'll mess with it and see how it behaves with the link.
xmo wrote:Unless the DIU is connected to a Centracom console ACIM for full Astro signalling capability or you are planning on encryption of the P25 traffic and want the link secure as well, I would consider relocating the DIU to the 'high' end. Then all you would need to pass up the link would be analog audio from the tone remote consoles.
If you need the DIU to be at the console location for either of those reasons, you might try fiddling with the analog and digital link check parameters. Also, as 515 indicated, there is a setting for how long the station will let the line stay analog before the modems attempt to re-sync. You should check that setting.
Casey KJ7XE
FYI - This problem was solved by removing all of the entries in the TRC command table for both the upper and lower analog UHF stations. This eliminates any falsing that may occur from the modem data on the line, causing one of the stations to stop passing audio. Since the stations are continuously keyed, there is no need for TRC on the stations.It has been working pretty good, although every week or so the ASTRO modem connection (not the RF link itself) will drop and not recover unless I cycle power on the UHF station at the high end. Any ideas? The UHF stations are both on dummy loads separated about 5 feet from each other, FM deviation is about 3 KHz and RSSI shows good on both ends.
Casey KJ7XE
Whats up.
Hi Casey looks like you online why arent you answering the emails or have you not been getting them?
Thursday is my deadline.
Joe
KC7LGT
Thursday is my deadline.
Joe
KC7LGT
We did some quick tests on this a while back - I remember the levels (particularly the data over the link) being touchier and more critical, there is less margin for error. Don't know how it would behave over a longer period of time. We'll probably start testing the backup system in narrow soon though because the NTIA deadline is 12/31/07...515 wrote:Guess I'll bring this thread back to life to ask this question...
Can the Astro Modems over a UHF Quantar link work when the UHF link station is programmed for 2.5 kHz narrowband? Has anyone tried it?
Casey KJ7XE
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I would be interested to know how it's done./\/\y 2 cents wrote:I can help you do this with PC's at each end rather than UHF radios in duplex constantly keyed
Steve
In my particular case we're limited to this type of solution because the mountaintop site is 40 miles away, no wireline connectivity, and no usable microwave link paths to the site - just AC power and that's pretty much it...
Casey KJ7XE
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I would suggest starband http://www.starband.com/
or Wild blue from the NRTC http://www.wildblue.com/
These will provide great remote backhaul capability.
Audio will be much cleaner, less noise and maybe you even have co-channel on the links (like many I work with have.) This will give you a clean audio circuit.
Latency is around 125-200ms. Not even noticed.
Steve
or Wild blue from the NRTC http://www.wildblue.com/
These will provide great remote backhaul capability.
Audio will be much cleaner, less noise and maybe you even have co-channel on the links (like many I work with have.) This will give you a clean audio circuit.
Latency is around 125-200ms. Not even noticed.
Steve