P25 and low band

[KF0SKV]

Is there technical limitations, besides antenna size, why P25 isn't used on low band, or is it being used?

 

[kilowa22]

Because of the possibility of interference caused by skip signals it makes it very difficult to use during band openings. Ham radio ops are using digital voice on 50 MHz and below, but the results are mixed and any interference makes digital unusable. Digital is 100% or nothing.

 

[vinzep491]

Well said.

 

[CoolCat]

"Low band" is being used less and less by public safety anyways. If public safety dept/agency is going to spend the money to upgrade all of their equipment to P25 digital, then chances are they are going to move up into the UHF band as well.

 

[ScannerDude244]

low band doesn't even need to be narrow band also.

 

[riveter]

Thing is, the whole point of low band is propagation propagation propagation. If it won't propagate long distances, there's no reason to use VL. Analog provides far superior weak-signal long-distance communication than any digital waveform. If security or digital clarity is required, SINCGARS FHSS does lose some distance compared to analog, but provides far superior anti-interference control to P25, as it is not restricted to one jammable frequency at a time. So, VL is almost always going to be used by the professionals in either plain analog mode or FHSS depending on commo requirements.

 

[902]

Thing is, the whole point of low band is propagation propagation propagation. If it won't propagate long distances, there's no reason to use VL. Analog provides far superior weak-signal long-distance communication than any digital waveform. If security or digital clarity is required, SINCGARS FHSS does lose some distance compared to analog, but provides far superior anti-interference control to P25, as it is not restricted to one jammable frequency at a time. So, VL is almost always going to be used by the professionals in either plain analog mode or FHSS depending on commo requirements.

Holy thread resurrection!

Although the decision is about 25 years old, I very strongly suspect the answer is: none of the above.

Around 1992, the major manufacturers stopped supporting VHF Low Band with top tier products. Some shops could build their own base stations with power supplies, tone or DC termination panels, external amplifiers (my favorite one to use was Henry Radio), and whichever mobile radio remained current production. Why?

From what I was told at the time, it was more to do with a strategic focusing on infrastructure-dependent technologies, like trunking. Along with that, higher frequency systems required more sites to because of propagation characteristics. And, fixed-end and subscriber units both required periodic technology refreshes. New firmware, "rebanding," COTS support equipment upgrades, etc. Look at what's coming down the road. It will be exclusively network dependent and that leaves room for plenty of recurring revenue sources.

By most estimation, VHF Low Band was a set-and-forget technology. Many of the radios in service continue to be Motorola Micor or Motrac, 40 or 50 years old and still, for the most part, reliable. That does not sell radios, nor does it sell service, until they start to go buggy from intermittents.

Low band is also fairly infrastructure independent. With efficient antennas, vehicles can talk about as far as they can with repeaters on higher frequencies.

Propagation was only a conveyance, not the rationale.

So, the investment in development was cut, and THAT's why there is no low band P25. Can it be done? Sure. Daniels base stations were modular and could have been configured to P25. You could even put an LTR controller on several low band repeaters and have a trunked system. But you'd have to piece together the radios yourself, and that talent pool of technicians who would even want to do that is rapidly retiring or dying off.

This shift in band usage has created effectively brown fields, and the concern for long distance propagation (right now, at least) is not very high.

Microprocessor noise and unintentional radiators are the current menace.

 

[riveter]

Holy thread resurrection!

Holy crap I didn't even notice that. I think there was a newer reply that got deleted or something, because I remember this being tagged unread.

*embarassed*

 

[902]

Holy crap I didn't even notice that. I think there was a newer reply that got deleted or something, because I remember this being tagged unread.

*embarassed*

LOL!!! Ah dunno! :lol:

 

[Darkstar350]

I actually have been pondering the same thing - as to why there really isnt any P25 on low band
Low band would actually be a decent option for P25 due to the characteristics of low band being efficient over long distances - and the nature of digital voice is that it is rather inefficient over longer distances so it would be a intresting match up...

I would imagine the reason would be the fact that P25 or any digital voice pretty much is required to be narrow band whereas low band is not - and i also think that manufacturers dont really want to make any major advances on low band equipment at the moment...

 

[Project25_MASTR]

I actually have been pondering the same thing - as to why there really isnt any P25 on low band
Low band would actually be a decent option for P25 due to the characteristics of low band being efficient over long distances - and the nature of digital voice is that it is rather inefficient over longer distances so it would be a intresting match up...

I would imagine the reason would be the fact that P25 or any digital voice pretty much is required to be narrow band whereas low band is not - and i also think that manufacturers dont really want to make any major advances on low band equipment at the moment...

A friend and I were talking about this earlier this month. Though, we weren't talking C4FM but more TDMA on lowband. Low power (25W max) smaller scale systems could actually fill a need for the ag industry in rural parts of the country at a lower cost of infrastructure compared to anything else. The big issue that arises, the primary companies that would be willing to manufacture the equipment are based in countries that don't have low band usage.

Sent from my SM-T350 using Tapatalk

 

[Darkstar350]

The big push for all these 7/800mhz inter operable P25 systems is going to create quite a bit of noise floor/interference so it would be valuable for manufacturers to start considering other options for P25 spectrum...

The thing about low band is as i mentioned it does have the ability to travel several miles and even over state lines depending on the conditions - and low band is also more prone to interference from things such as baby monitors and power lines so i dont know if/how that would affect digital voice because like someone else pointed out - with digital voice its either all or nothing...

Much of the fire dispatching and paging is my area is actually still done on low band - and has been efficient for many years but what alot of departments are doing now due to the decrease in support for low band pagers is they will simulcast their pager tones and dispatch over a high band frequency as well - and that is also because most of the tac/fireground channels are on highband portables therefore making the dispatch channel compatible with the portables...

 

[Project25_MASTR]

The big push for all these 7/800mhz inter operable P25 systems is going to create quite a bit of noise floor/interference so it would be valuable for manufacturers to start considering other options for P25 spectrum...

The thing about low band is as i mentioned it does have the ability to travel several miles and even over state lines depending on the conditions - and low band is also more prone to interference from things such as baby monitors and power lines so i dont know if/how that would affect digital voice because like someone else pointed out - with digital voice its either all or nothing...

Much of the fire dispatching and paging is my area is actually still done on low band - and has been efficient for many years but what alot of departments are doing now due to the decrease in support for low band pagers is they will simulcast their pager tones and dispatch over a high band frequency as well - and that is also because most of the tac/fireground channels are on highband portables therefore making the dispatch channel compatible with the portables...

But digital isn't all or nothing. Forward Error Correction...some modes do it better than others but many times I've noticed coverage increases on digital versus analog.

 

[Darkstar350]

Well not quite "all or nothing" i suppose - but with digital voice there really is no "coming in low" or distant sounding - generally you either hear the person talking or its a complete scramble type noise which is known as a "bit error"
I would imagine this is the type of thing radio manufacturers are in the process or are looking to advance on thus "error correction"

The noise floor on low band in my area is rather low - some fire dispatching is done on 46mhz and some of the highway/snow plow depts. are on 47mhz and there isnt that great a deal of activity there but going even lower then that - say ballpark 37mhz is really nothing and i would guesstimate that much of the country is like this so i could see low band definitely being valuable for areas where a lot of the other radio spectrum is congested...

 

[RFI-EMI-GUY]

Portable radio operation on low band is pretty much an impossibility. Mobile only systems are practical. However the noise floor is very unpredictable and you need to design the system with the expectation that some sites will get hammered by either manmade or natural noise sources. Also the mobile is susceptible to noise. It used to be that diesel trucks got along well with low band, but now the vehicle electronics are troublesome.

 

[KC3ECJ]

Portable radio operation on low band is pretty much an impossibility. Mobile only systems are practical. However the noise floor is very unpredictable and you need to design the system with the expectation that some sites will get hammered by either manmade or natural noise sources. Also the mobile is susceptible to noise. It used to be that diesel trucks got along well with low band, but now the vehicle electronics are troublesome.

Could have low powered cross band mobile repeaters that would connect to handhelds over VHF high or UHF.

 

[Project25_MASTR]

Could have low powered cross band mobile repeaters that would connect to handhelds over VHF high or UHF.

Or X10DRs depending on application. I've sold some to some small town (less than 500 residents) PDs for use in their cruisers and a few to TxDOT. TxDOT really seems to like the battery life compared to hand helds. Very few trucks still have 47 MHz radios in them still…all of the Texas statewide agencies have standardized on high band now.

 

[Darkstar350]

Thats another thing - portable capability
I dont know of any company that makes low band portables and if there is i would imagine they are probobly old and the size of a brick with rather large telescoping antennas...

A vehicular/crossband type repeater system would also have to be put in place so thats just another obstacle - but i still dont think manufacturers should abandon low band entirely...

 

[nd5y]

I have never seen a low band hand held with a telescoping antenna. The ones I have seen had 12" to 18" rubber duckies. Just like a high band antenna but longer.

 

[Darkstar350]

I may be thinking of some outdated fire dept. pictures with these big "brick" style radios and i think some of them may have had telescoping antennas but yeah even a footlong or so rubber duck would be sufficient for low band i suppose
Not sure if moto does/did make HT1250 style low band portables...