Nevada County SO to move to 450 Mhz!

[digitaljim6]

Do you hear all of AMR's non-emergency inter-facility transfers and wheelchair van traffic on AlCo, too? If not, look for some other method, probably outside of the County's system.

I have only seen/heard instances where AMR is allowed to "use" city/county channels while performing contract EMS services to the city/county. My point is that some of AMR's (or any other private ambulance company's) activities which are not covered under the contract may disqualify them from sharing the city/county/state systems depending on the channels used. "Sharing" in this case means the private company using the government system for the private company's own activities that are unrelated to any service contract arrangement with the government.

For example, there are 700 MHz channels which are only available to government organizations and not to private companies who offer their services to the public 90.523(d). A private company could not legally "share" on such a channel while engaging in its own activities because it isn't otherwise eligible to hold a license on that channel.

In Alameda Couny, AMR dispatch uses the Alameda Public safety system for they radio system and dispatch. I also here AMR in San Mateo County Public safety system. Also most public safety company have back channels to talk and those are also in use on the Public Safety system.

All I said to start this off was I do not see anything about AMR. As you can see the gov and AMR have joined together on a radio system. I did not say the gov would foot the bill for AMR radio system, maybe they could join in on it. They must rent the system coverage from the Counties.

 

[drouse3]

I read Alameda County has 132 angenies on the Public safety system. I do hear a lot of non emergency traffic, Most of it is transports.
My nieghbor works for the Oakland FD and AMR partime, maybe I should ask him whats going on with the radios. Remember Alameda County starting a p-25 project.

 

[digitaljim6]

That would be helpful. One question would be if AMR uses the AlCo system for traffic which is not part of their contract with the county.

I read Alameda County has 132 angenies on the Public safety system. I do hear a lot of non emergency traffic, Most of it is transports.
My nieghbor works for the Oakland FD and AMR partime, maybe I should ask him whats going on with the radios. Remember Alameda County starting a p-25 project.

 

[BirkenVogt]

Well, here's a start.

http://www.placer.ca.gov/news/2005/11-10-05-radio-system-funds.htm

Back to the subject

I was reading that and also have noticed that the SO is in a commercial site on Oregon Peak there. Just another example of the apparent lack of planning/waste of money on this system. The Comsites site is on the other side of the hill from the CDF site and they have to pay rent there, and they had to put up their own antenna. If they had used the (huge and mostly empty) CDF site they would be on the correct side of the hill for the area they cover, the could have used the combiner and antennas already there, and not had to pay rent (I presume)

They are in the other CDF sites but they are using their own duplexers and antennas. Also the Motorola equipment they use is 24v which means they have to have their own batteries since there is no 24v battery power onsite already but there are racks of 12v batteries for everyone to use. The batteries they use are a pair of small 12v smaller than car batteries so they better hope the generators stay online in the event of an emergency.

The whole system is pretty disappointing when they could have done it so nicely integrating with what was already there, instead they did it all their own way and evidently failed. So the county pays again. And again.

Birken

 

[digitaljim6]

There is probably a good reason why the state site is mostly empty. The state doesn't give space away. Everybody has to pay (unless you're a CDF VIP ham group) - there's no free lunch. I suspect the SO would have had to pay a connection fee for the initial combiner hook-up, too.

The bureaucratic side might have been too much as well. They probably got access arranged in a week at the commercial site instead of months to get through the red tape for the state site.

The 24V battery thing is a non-issue. The primary reason for batteries at a generator-equipped site is to cover the seconds between commercial supply failure and transfer to generator. If you run out of fuel or have an actual failure, a relatively small plant can give you hours of operation for dispatch-type use. The trick is to train the dispatchers to recognize what the power fail beep means and to take immediate action when they hear it.

Double the voltage means half the current for the same power so the 24V plant can be "wimpy" and still be adequate for some period of time. As long as you have year-around access to the site for fuel delivery and generator repair, you can usually get by with minimal battery power. You can use smaller wire sizes as you increase voltage, too, as I2R losses drop - less goes up in heat.

Did they fail because of the way the individual sites are installed or because of where the sites are or aren't? Or because of improper use of the system? If they are expecting portable coverage everywhere, they would need a TON of voting receivers scattered all over the place. Perhaps the system design was trimmed to fit the dollars instead of the dollars being found to achieve the needed level of service.

Back to the subject

I was reading that and also have noticed that the SO is in a commercial site on Oregon Peak there. Just another example of the apparent lack of planning/waste of money on this system. The Comsites site is on the other side of the hill from the CDF site and they have to pay rent there, and they had to put up their own antenna. If they had used the (huge and mostly empty) CDF site they would be on the correct side of the hill for the area they cover, the could have used the combiner and antennas already there, and not had to pay rent (I presume)

They are in the other CDF sites but they are using their own duplexers and antennas. Also the Motorola equipment they use is 24v which means they have to have their own batteries since there is no 24v battery power onsite already but there are racks of 12v batteries for everyone to use. The batteries they use are a pair of small 12v smaller than car batteries so they better hope the generators stay online in the event of an emergency.

The whole system is pretty disappointing when they could have done it so nicely integrating with what was already there, instead they did it all their own way and evidently failed. So the county pays again. And again.

Birken

 

[BirkenVogt]

True I don't know what the state charges. However it was good enough for USFS, BLM, CHP, County Fire, FBI, DEA, DFG, animal control, NOAA, CalTrans, State Parks, etc.

Sure the batteries' stated purpose is to carry it over until the generator can start but these sites are mountain top and get snowed over all the time. If anything happened they would be SOL a lot sooner than the other users. It's not the voltage that counts but the total watthours contained in the batteries. The SO has only two very small batteries compared to several racks full for the general site so they won't be on near as long. They should have used a 12v-24v convertor instead. Every rack already has pre-wired to it enormous wires and breaker panels from the 12v, all they had to do was hook it up. Sure double the voltage means half the current but you still have to have the same amount of batteies to get the same run time, they are just connected series instead of parallel.

I have not done a detailed analysis of their problem but I have a fair bit of experience in this. It sounds to me from monitoring them and from looking up licenses on the frequency that their input freq was poorly chosen and is suffering interference from co-channel users across the valley. This because I hear a field unit talking, then I will hear a heterodyne on their signal. Could be intermod too but I doubt it.

The second thing is, I think the deputies were all too used to low band, and having to switch to the correct repeater is new to them.

Like I said, it's the same system that county fire and CDF have been using since the 80s on the same mountains and our portable coverage is pretty solid, and mobiles are basically 100%. There used to be some UHF around here but it has pretty much died off in favor of high band especally because of the refarming and narrowbanding.

Birken

 

[Kirk]

Kenwood makes some pretty nice low band mobiles, Pyramid makes some pretty nice vehicular repeaters... does anyone make LB repeaters anymore?

I'm kinda curious why so many agencies are anxious to replace systems that work well. I think people are equating "low band" with "low tech" and that simply isn't the case.

 

[digitaljim6]

The only non-state/fed user at the state site, then, is animal control? The rest that are there can afford to pay whatever - Arnold and George have deep pockets.

24V is what most commercial microwave equipment uses, at least it's been that way for the last few decades. Those systems usually have their own batteries and rectifiers separate from everybody else anyway. Maybe there is a buy-in cost to use the site's plant and that wasn't in the budget.

If the snow-in issue is a long-term thing (like sites which are only reachable by air or snowcat from November to May), the site should be equipped with enough fuel to run for months. One site I worked on had enough fuel (propane, in order to avoid contamination and pollution issues) to run everything for 4 months because of the winter access problem. If you have batteries for 12 hours and your commercial power is out for weeks, 12 hours doesn't really mean that much. You still need the generator after the first day or so, depending on the plant size.

So the bottom line seems to be that the "failure" doesn't have anything to do with site selection or batteries. It is due to poor freq choice and user training.

True I don't know what the state charges. However it was good enough for USFS, BLM, CHP, County Fire, FBI, DEA, DFG, animal control, NOAA, CalTrans, State Parks, etc.

Sure the batteries' stated purpose is to carry it over until the generator can start but these sites are mountain top and get snowed over all the time. If anything happened they would be SOL a lot sooner than the other users. It's not the voltage that counts but the total watthours contained in the batteries. The SO has only two very small batteries compared to several racks full for the general site so they won't be on near as long. They should have used a 12v-24v convertor instead. Every rack already has pre-wired to it enormous wires and breaker panels from the 12v, all they had to do was hook it up. Sure double the voltage means half the current but you still have to have the same amount of batteies to get the same run time, they are just connected series instead of parallel.

I have not done a detailed analysis of their problem but I have a fair bit of experience in this. It sounds to me from monitoring them and from looking up licenses on the frequency that their input freq was poorly chosen and is suffering interference from co-channel users across the valley. This because I hear a field unit talking, then I will hear a heterodyne on their signal. Could be intermod too but I doubt it.

The second thing is, I think the deputies were all too used to low band, and having to switch to the correct repeater is new to them.

Like I said, it's the same system that county fire and CDF have been using since the 80s on the same mountains and our portable coverage is pretty solid, and mobiles are basically 100%. There used to be some UHF around here but it has pretty much died off in favor of high band especally because of the refarming and narrowbanding.

Birken

 

[BirkenVogt]

There are lots of other tenants. In the interest of brevity I won't go through them all. But on the other mountaintops the SO is in the state vault and there is even more commercial stuff available there. Just Oregon Peak where they are not. Also County Fire (who I service) is a very low-budget agency and they have been there since the beginning. I ought to find out how much they pay. Anyway Oregon Peak has no microwave, only 12v. The other sites that do have microwave do not have any 24v supplies established. Lots of microwave though. All of it is running on equally large -48v supplies with other massive banks of batteries.

I am sure the power supply has nothing to do with why they want to change it. However I find it indicitive of the kind of work they must have done. They came in and set up their own power supplies, duplexers (which I also will not use at a congested site, instead using preselectors, combiners and split antennas), their own antennas and what do you know. It does not work as expected. They may have saved some money by not coupling onto the State multicouplers and antennas but what did they gain? Evidently a system that did not work very well. Either that or there are more sinister forces at work which is a distinct possibility if you get my drift. I mean, who buys Motorola any more at 5x the price when other manufacturers have such competitive products, unless there are other incentives?

Birken

 

[digitaljim6]

Nothing wrong with proper duplexers. Since the same laws of physics apply to both approaches, a duplexer with passband and rejection characteristics equal to the combiner/multicoupler approach will work exactly the same. In some cases, the receive half will perform better in a duplexer-based arrangement because it will be single-frequency instead of a window. You may have to add a circulator or two (isolator) between the transmitter and the duplexer to keep foreign energy out of the transmit half, of course.

Perhaps there were combiner/channel compatibility problems at the state site because of Yuba County's VHF stuff.

So now it's not a bad input freq and user training that cause the "failure", but the antenna system and evil vendor forces?

 

[BirkenVogt]

Hey man lighten up!

It is very hard to imply my tone of voice in what I am saying. Read a little into it. Also I am covering a lot more topics than just simple RF problems with the system.

IIRC the duplexers are TX/RX brand who I consider to be a top notch manufacturer but they are only as good as the installation and the antenna and the location of the antenna. Also the manufacturer of the duplexer has to be informed of conditions at the site of course and if they were given incomplete or incorrect information then it is not going to work as advertised.

In a perfect world a duplexer would work as good as a split system but there are a couple of issues to consider.

First is to provide the required degree of isolation (input signal less than -50 dBm) on a 100w system IIRC the transmit/receive isolation has to be around 100 dB I think. 100w being roughly +50 dBm. With a duplexer this means that the loss on the receive side will have to be higher than if it was a simple cavity system because the transmit energy is coupled onto the same antenna wire. With properly separated antennas you get about 50 dB of isolation there alone so that does not have to be done with filters. Which means that the receive signal gets through that much stronger. IIRC again, they are using 4 or maybe 6 8" cavities on the duplexer which makes me wonder. Another issue is they are only running 735 KC of split on the transmit/receive freqs.

Second is that with the transmitter coupled onto the same cable, any connection that is not perfect (i.e. any mechanical connection) is a potential wideband noise generator. Basically making a small arc that becomes broadband. The antenna can do this too. As things age it becomes worse obviously.

Third, the cost of a duplexer is increased (or its performance decreased) on a congested site because part of its design has to be to notch its particular transmitter from its receiver. It also has to supress the other transmitters too.

To me, duplexers are a solution for isolated sites where no other garbage is flying around. Once you are in it together with a bunch of other users, it is better to work together than to have each user "doing his own thing".

Birken

 

[northzone]

Quote:
{24V is what most commercial microwave equipment uses, at least it's been that way for
the last few decades. }

Wrong, commerical microwave is minus 48 volts, been that way for decades.

Quote:
{Nothing wrong with proper duplexers. Since the same laws of physics apply to both
approaches, a duplexer with passband and rejection characteristics equal to the
combiner/multicoupler approach will work exactly the same. }

Not even close. In a transmit combiner you typically lose 3db (half your power) up to 7db for each transmitter connected to the combiner, in a duplexer you usually lose about 1 to 1.5 db. The same laws of physics do not apply because they do not function the same at all.

 

[digitaljim6]

Well, no. The AT&T microwave sites (now decommissioned) that spanned cross-country for AUTOVON since the 1960's had NO -48V transmission equipment - only -24V equipment. That ran the radios and multiplexing stuff, alarms, everything. -48V plants were added when DS-3 encryption equipment was installed or if a junction site had call-switching equipment, too. Most of the sites never had 48V plants. The orderwire equipment needed it so they had a small 24-48 converter in the orderwire rack for that equipment only.

As I recall, Motorola's original Starpoint microwave was 24V. Seems to me that all of the Farinon that the state used (uses) is also 24V.

I disagree. The function is the exactly the same - filtering and isolation. As for insertion loss, it's dependent on the frequencies of the combiner's other legs and how the cavity loops are set. If there is enough separation between frequencies, you can get lower insertion losses. The adjustable loops give you control over the tradeoff between insertion loss and skirt steepness (bandwidth).

If you're burning up 7db of your power, complain to your system designer or move some of your tenants' transmitters to other combiners. Check the critical length cables between the junction and the cavities. A little tweaking there can make monumental differences in performance.

You might even have better luck in some cases with buss combining rather than the common star-junction method.

Quote:
{24V is what most commercial microwave equipment uses, at least it's been that way for
the last few decades. }

Wrong, commerical microwave is minus 48 volts, been that way for decades.

Quote:
{Nothing wrong with proper duplexers. Since the same laws of physics apply to both
approaches, a duplexer with passband and rejection characteristics equal to the
combiner/multicoupler approach will work exactly the same. }

Not even close. In a transmit combiner you typically lose 3db (half your power) up to 7db for each transmitter connected to the combiner, in a duplexer you usually lose about 1 to 1.5 db. The same laws of physics do not apply because they do not function the same at all.

 

[digitaljim6]

OK. .

Hey man lighten up!
Birken

 

[BirkenVogt]

Bus combining is nifty. Sure makes for a neater rack especially when you get to 7+ transmitters...only thing then is you have to worry about the antenna catching on fire

Another thing I did not mention is when you do like the SO did and put a duplex T/R antenna on a tower that already has high band antennas on it, you have 3 options on where to locate it, all of them bad.

First you could put it on the 120' level where its transmit would be going right down the throat of the multicoupled receive antenna. The other users would probably not appreciate this.

Next you could put it on the 80' level where everyone elses transmitter would be blasting into your receiver. It would be tough to get the 100 dB of isolation from the other transmitters with the antennas on the same level separated by only a few feet. This is what they did I think.

Finally you could put the antenna on the 40' level or lower...and get the coverage that goes with that.

What I am basically trying to point out in my ramblings of this thread, is that apparently nobody really thought very hard about this system all the way through. And also, it's possible that somebody was selling more equipment (antennas, feedline, installation labor, etc) than was really necessary. I can't imagine tower rent for a whole new antenna and feedline would be cheaper than going on a combiner either...

Birken

 

[digitaljim6]

I don't doubt that at all. What a lot of pepople also don't realize is that you get far more isolation if the antennas are located directly above/below each other, and that means close enough to directly above/below to stay in the each antenna's "cone of silence" (thanks agent 99). Anything else and you lose much of the isolation. If I remember right, 1 foot of vertical is worth something like 100-200 feet of horizontal.

Maybe if the FCC went back to requiring licensed techs, this sort of thing wouldn't happen as often.

 

[BirkenVogt]

Cone of silence...heh. Been a long time since that one....

That, I think, is the main reason for using combiners and split level antennas, that way everyone's transmitter stays out of the other receivers but then you get one loose cannon who has to do it "their way" and it all goes out the window.

ANYWAY, BACK TO THE SUBJECT....

The City of Grass Valley as I understand it is using 450 MHz for their MDTs and 156 (literally; 156.0000) for their voice. I hope this news that this thread turns out to be that same situation, and they retain their high band for voice, otherwise, it is going to be a big hassle.

Birken

 

[califzeph]

Little back-woods Grass Valley has MDT's?

 

[BirkenVogt]

So I've been told....

Birken

 

[mkewman]

affirm. grass valley pd uses mdts... keep in mind, the actual city of grass valley isn't that woodsy, however nevada county is.