P25 and low band

[nd5y]

I don't know if any were HT1250s but I have seen plenty of old Motorola low band hand helds at hamfests over the years.

 

[Project25_MASTR]

Low band HT750…came from South Plains Communications in Lubbock, client is a gin just southwest of town.

As mentioned, the portable antennas are a little bit unwieldy. TxDOT in the Lubbock district was using TK-690s, TK-6110s, and VX-6000s for district wide communications and high band for county maintenance. Maintenance was using high band portables for ground work and the supervisors generally had both a low band and high band radio in the trucks to work everything prior to the high band migration.

That being said, I don't believe Motorola currently sells any low band (they still support the Pro series stuff and PM1200 though). Kenwood still has the x90 line. Not sure if Vertex is still doing low band.

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[Darkstar350]

^ Thats a heck of a piece - the antennas like twice the length of the handheld itself
What would be the power on something like that?

Yeah i was also thinking Kenwood may still make some stuff more in the way of low band - but im pretty sure Motorola is still making some CDM1250 low band base units...

Come to think of it now i could have sworn that i did pick up some P25 somewhere in 40mhz
It may have been "bleed over" from one of the military bands perhaps?
I guess the big question is - is there any low band radio in existence that is even P25 capable...

 

[nd5y]

I guess the big question is - is there any low band radio in existence that is even P25 capable...

Harris makes some military multi-vwaveform radios that cover down to 30 MHz and are P25 capable. Probably Thales and Datron have them too.

 

[wyShack]

I have not been involved in low band for years but back when I was repeaters were not allowed -just remote bases. have the rules been updated? If not, I would guess the inability to even think about repeaters would make a system designer pause.

 

[RFI-EMI-GUY]

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

Yep you can do that. CHP, FDOT have those.

 

[RFI-EMI-GUY]

I don't know if any were HT1250s but I have seen plenty of old Motorola low band hand helds at hamfests over the years.

Yup the HT-1250 came in Low Band, I programmed a couple.

 

[nd5y]

I have not been involved in low band for years but back when I was repeaters were not allowed -just remote bases. have the rules been updated? If not, I would guess the inability to even think about repeaters would make a system designer pause.

I have never heard of repeaters not being allowed on low band. I remember hearing the Michigan State Police, Tennessee Highway Patrol and some sheriff depts. in California and Florida and Tarrant County, TX on repeaters back at least 30 years ago.

 

[Project25_MASTR]

I have never heard of repeaters not being allowed on low band. I remember hearing the Michigan State Police, Tennessee Highway Patrol and some sheriff depts. in California and Florida and Tarrant County, TX on repeaters back at least 30 years ago.

Stashed away at what has become of Reese AFB I have one of DPS's old GE Mastr Pro stations with dual receivers (one high band). Also have Lubbock county's old 36 MHz Minor station (remote base) sitting next to it.

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[wyShack]

My mistake-guess you do learn something new every day. I just never saw anything but remote bases set up.

 

[Project25_MASTR]

My mistake-guess you do learn something new every day. I just never saw anything but remote bases set up.

There were a ton of low band repeaters in Texas at one point (25 from TxDOT alone, one for each district)...that's also one reason why Texas band plan (amateur) calls for 1 MHz offsets while ARRL calls for 500 kHz in 6m, all the surplus state agency stuff in the 47 Mhz range was setup for 1 MHz offsets.

 

[nd5y]

Not all of the TxDOT districts had repeaters. They were mainly in west TX. Where did you hear that? and TxDOT's repeater inputs were in the upper 45 MHz range, not -1 MHz.

 

[902]

I have not been involved in low band for years but back when I was repeaters were not allowed -just remote bases. have the rules been updated? If not, I would guess the inability to even think about repeaters would make a system designer pause.

No, there is no such rule. A number of places had low band repeaters over the years, but most of them had gone away because of higher spectrum. The issue with low band repeaters was efficiency. For a single site to be effective, there had to be a lot of vertical separation between antennas or a duplexer network that usually occupied a space the size of a closet (or more). A low band cavity can be the size of a water heater depending on Q. A DB4042 can is over 6 ft. tall and 10 inches wide in the 30 MHz range.

Antennas function within a narrow window, too. Base antennas are fairly narrow (unless you're using a military surplus discone), Motorola used phasing harnesses to pick between two low band mobile antennas for the appropriate range between them, and the HT antennas used to have tunable slugs that needed to be adjusted for the maximum field strength. They didn't work well because there usually wasn't sufficient counterpoise on the radio and the antennas were detuned by various materials, like steel framing, rebar and metalized windows.

But you could have voting receivers, you could do simulcast or transmitter steering, and the architecture was still solid.

 

[902]

Not all of the TxDOT districts had repeaters. They were mainly in west TX. Where did you hear that? and TxDOT's repeater inputs were in the upper 45 MHz range, not -1 MHz.

What were they, 45 in and 47 out?

 

[nd5y]

What were they, 45 in and 47 out?

Yes.

 

[RFI-EMI-GUY]

No, there is no such rule. A number of places had low band repeaters over the years, but most of them had gone away because of higher spectrum. The issue with low band repeaters was efficiency. For a single site to be effective, there had to be a lot of vertical separation between antennas or a duplexer network that usually occupied a space the size of a closet (or more). A low band cavity can be the size of a water heater depending on Q. A DB4042 can is over 6 ft. tall and 10 inches wide in the 30 MHz range.

Antennas function within a narrow window, too. Base antennas are fairly narrow (unless you're using a military surplus discone), Motorola used phasing harnesses to pick between two low band mobile antennas for the appropriate range between them, and the HT antennas used to have tunable slugs that needed to be adjusted for the maximum field strength. They didn't work well because there usually wasn't sufficient counterpoise on the radio and the antennas were detuned by various materials, like steel framing, rebar and metalized windows.

But you could have voting receivers, you could do simulcast or transmitter steering, and the architecture was still solid.

I was the initial designer of the FDOT 47 MHz system and all those repeater issues were addressed. Separate TX and RX antennas, each with band pass/reject filtering.

Localized site noise was a big problem. We measured noise floor at a number of locations to come up with a noise floor for modeling overage. It was highly variable. It seems the repeater sites get hammered by power-line noise and the mobiles get a lot of ignition noise from other vehicles.

The FDOT 47 MHz system is voted (JPS SNV-12) and is multicast. The mobiles in each zone transmit on a common repeater input frequency and the repeaters transmit on different frequencies. The mobiles are designed to non-priority scan for an acceptable (no RSSI capability, AND squelch, "tight" squelch) site. Portables via VHF crossband repeater. The system as designed used E&M signalling and careful CTCSS selection to maximize access time and eliminate receiver interference. I changed jobs toward the end, and the customer decided upon himself to use EIA keying of stations and changed to DCS squelch signalling, so I doubt the system now works as quickly and smoothly as I had envisioned. DCS is terrible when you have co-channel interference. I doubt the careful frequency planning I performed would stand up to the nasty band enhancements that will occur from time to time.

 

[902]

I was the initial designer of the FDOT 47 MHz system and all those repeater issues were addressed. Separate TX and RX antennas, each with band pass/reject filtering.

Localized site noise was a big problem. We measured noise floor at a number of locations to come up with a noise floor for modeling overage. It was highly variable. It seems the repeater sites get hammered by power-line noise and the mobiles get a lot of ignition noise from other vehicles.

The FDOT 47 MHz system is voted (JPS SNV-12) and is multicast. The mobiles in each zone transmit on a common repeater input frequency and the repeaters transmit on different frequencies. The mobiles are designed to non-priority scan for an acceptable (no RSSI capability, AND squelch, "tight" squelch) site. Portables via VHF crossband repeater. The system as designed used E&M signalling and careful CTCSS selection to maximize access time and eliminate receiver interference. I changed jobs toward the end, and the customer decided upon himself to use EIA keying of stations and changed to DCS squelch signalling, so I doubt the system now works as quickly and smoothly as I had envisioned. DCS is terrible when you have co-channel interference. I doubt the careful frequency planning I performed would stand up to the nasty band enhancements that will occur from time to time.

DCS takes a lot longer to decode, as well. I used it in some FXO applications in the Midwest and noticed that its timing was worse than lower CTCSS tones for opening. I had consistent clipping on the system I was directed to build, which drove me nuts.

Did you get any increase in the noisefloor because of precipitation? Heard that was problematic and even read about one agency wrapping their antenna elements with Scotch 33 to minimize the static charge of the raindrops.

You certainly designed an interesting system. We had a similar 6 meter amateur system in NJ, which was originally supported by employees of the Garden State Parkway. It was in heavy use about 26 years ago. It used the microwave system back to a comparator, which fed back down the microwave to transmitters that hop-scotched along the Parkway. One common input, with hop-scotching transmitters so the operator only had to switch between A and B for whichever site had better capture. No matter where you were in NJ, you were always within one of the outputs. I thought it was nothing short of fantastic, and had a Syntor-X in my truck at the time that I could push buttons when I started hearing noise from the site I was listening to. But, people retire, move on, etc. I'm not even sure it's in operation anymore.

I think you and I know each other in real life.

 

[RFI-EMI-GUY]

DCS takes a lot longer to decode, as well. I used it in some FXO applications in the Midwest and noticed that its timing was worse than lower CTCSS tones for opening. I had consistent clipping on the system I was directed to build, which drove me nuts.

Did you get any increase in the noisefloor because of precipitation? Heard that was problematic and even read about one agency wrapping their antenna elements with Scotch 33 to minimize the static charge of the raindrops.

You certainly designed an interesting system. We had a similar 6 meter amateur system in NJ, which was originally supported by employees of the Garden State Parkway. It was in heavy use about 26 years ago. It used the microwave system back to a comparator, which fed back down the microwave to transmitters that hop-scotched along the Parkway. One common input, with hop-scotching transmitters so the operator only had to switch between A and B for whichever site had better capture. No matter where you were in NJ, you were always within one of the outputs. I thought it was nothing short of fantastic, and had a Syntor-X in my truck at the time that I could push buttons when I started hearing noise from the site I was listening to. But, people retire, move on, etc. I'm not even sure it's in operation anymore.

I think you and I know each other in real life.

Yeah and the DCS is very unreliable when you have co-channel interference which will likely happen when the propagation gets enhanced. I think the decoders have to see three valid word periods to open squelch. Precipitation static is real I have heard it at 2M on my satellite array. We did not wrap these low band antennas. Maybe should have. That 6 Meter system sounds like a real power house. Maybe so. I worked for the "M", then a large PS LMR consulting company with its HQ in NJ, then Bearingpoint (800 rebanding) up until the end of their (expected) bankruptcy.

 

[garyscot]

As a dinosaur tech I have read these posts with a smile on my face. 99% of you guys have grown up in the tin ear digital only era and have no idea what great audio and extended 50 to 100 mile two-way coverage is really like. Low band works fine if designed with a little old school knowledge (last seen engraved into some Egyptian pyramid internal wall passages) and new school interference software. It was the staple of two-way for many large systems including San Diego and Los Angeles county sheriff's for many years - before the 800 Moto Magic Men, FCC bureaucrats and their budget busting sales pitch wet dreams came along in the 80's. It is still the state-wide California Highway Patrol choice for a reason - it covers a lot of nasty terrain with one or two repeater/ base sites per channel and just works. The mess California has made out of the current P25 digital portable-analog two-way system is not the fault of 30-50Mhz radios or radio waves (I will stop comments there).
Repeaters are fine at any spread over 600Kc input-output, if the tech understands transients, desense, shielding, grounding and has antenna experience. They are just large physical installations by necessity. Portables and pagers do not work. Because getting a strong 5 or 6 foot long 1/4 wave signal into and out of a concrete & steel building is an exercise in futility. So a simple VHF or UHF mobile-portable extender for short range back to the vehicle is the easy fix key. Digital code-key and simple voice inversion encryption also works very nicely on low band systems as well.

 

[902]

As a dinosaur tech I have read these posts with a smile on my face. 99% of you guys have grown up in the tin ear digital only era and have no idea what great audio and extended 50 to 100 mile two-way coverage is really like. Low band works fine if designed with a little old school knowledge (last seen engraved into some Egyptian pyramid internal wall passages) and new school interference software. It was the staple of two-way for many large systems including San Diego and Los Angeles county sheriff's for many years - before the 800 Moto Magic Men, FCC bureaucrats and their budget busting sales pitch wet dreams came along in the 80's. It is still the state-wide California Highway Patrol choice for a reason - it covers a lot of nasty terrain with one or two repeater/ base sites per channel and just works. The mess California has made out of the current P25 digital portable-analog two-way system is not the fault of 30-50Mhz radios or radio waves (I will stop comments there).
Repeaters are fine at any spread over 600Kc input-output, if the tech understands transients, desense, shielding, grounding and has antenna experience. They are just large physical installations by necessity. Portables and pagers do not work. Because getting a strong 5 or 6 foot long 1/4 wave signal into and out of a concrete & steel building is an exercise in futility. So a simple VHF or UHF mobile-portable extender for short range back to the vehicle is the easy fix key. Digital code-key and simple voice inversion encryption also works very nicely on low band systems as well.

Hi Gary, glad to meet you! I used to listen to CHP and a number of other California agencies on low band when I lived in New Jersey back in the day. I go back to the early 80s in two-way, have been a ham for a little longer than that, and an SWL/scanner listener since the early 70s.

P25 phase 1 audio isn't so bad to me. Neither is decoded ProVoice. I've got no experience with P25 phase 2 audio to note whether it sounds different or not. I have a great deal of problems understanding cellular telephone audio. It's worse than tin ear. I strain to make out what people are saying because of the high compression (and my hearing). Everyone on cellular sounds like they have marbles in their mouth to me. So, to adapt, I've shut off the ringer and only use SMS on mine. iDEN "direct connect" sounded that way to me, too. Let's hope voice over LTE sounds better (since it promises to be all things to everyone, and that chokes down bandwidth, I'm not holding my breath for that).

And RFI-EMI-GUY, hope to see you in Orlando in August.