Low Band Voted System

70cutlass442

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Admin- Please move to another category if you feel the need.

Overview:

Build out wide area voted network using spare and readily available commercial grade parts.

History:

Low band has always been intriguing to me. Its unique characteristics and history have had my attention for years. My original plan was to build out a 6M system however, some of my friends that have interest in such a plan do not have their ham license. With the availability of 100+ watt mobiles and the ability to operate in wide band I thought that getting a business license in the low band spectrum would be a fair compromise to get others on the air without. Additionally, I have had an interest lately in old commercial two-way equipment which naturally fits the low band theme.

Parts:

I have in my basement an assortment of CDMs, Maxtracs, MaraTracs, and Kenwood TKxxxx (the model escapes me). I also have an assortment of voters to choose from ranging from the GE voter (white and black chassis), a raven 8 channel, or a few Raytheon SNV12s. Also available are UHF CDMs and like radios that can be used for up/down link radios or the Chinese RoIP boxes (we have a microwave network spanning numerous sites for our existing commercial system).

Restate:

At our disposal we have a 500' commercial tower in SE Wisconsin. Throughout the area we have access to other towers, builidngs, and homes at higher elevations.

Goal:

Using the above equipment, build a central TX site (500' tower) with four RX sites. RX sites can be linked via UHF or via IP. UHF links would utilize existing UHF channels licensed to us for those sites.

Stay tuned for updates. We are discussing frequencies with the coordinator and will likely be using the 42-50 spectrum. Any input and ideas are appreciated.
 

prcguy

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Voted receiver sites with a single high power transmit site is more in line with hand held use in the field and you are proposing using high power mobiles, so that's not a good fit for voting.

I think with the IP technology available, why not build multiple repeater sites on different frequency pairs and link them all via the Internet? That way all receive sites will have an accompanying transmitter with the same coverage as the receiver and all sites will transmit everything heard from anywhere to everywhere. Might not be easy to license but it works really well on the amateur bands.

Kind of like the amateur "WIN System", but please don't let your system become a big bloated system that only exists to consume frequency pairs, feed itself and its idiot owners and control ops egos. Or maybe I should say control freaks egos. Its a great example of a good idea gone way wrong.
 

kb8vkg

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There's a 6m wide area repeater in NE Ohio, near Cleveland that's been in operation for over 35 years. It's a single standalone transmitter site with 15 or so receive sites up to 75 miles away from the transmitter.. All linking is done over UHF. It's an impressive system with no club affiliation and was constructed by and is maintained by current/ex radio techs.
A long article can be found at:
 

RFI-EMI-GUY

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I designed the Florida DOT statewide multicast system. It consists of several large district zones of low band 47 MHz multicast. Each zone has a single repeater input frequency in the 45 MHz range and multiple 47 MHz output frequencies. The mobiles scan on a non priority basis to receive a suitable TX site. Voting is done using Raytheon JPS SNV-12 voters. Backhaul is almost entirely via microwave.

It was never designed as a portable system, it was designed to replace a 100W simplex mobile system that was highly fragmented and had little utility in providing wide area critical communications. The impetus was a hurricane that took out cellular and NEXTEL communications, leaving DOT with poor communications during road clearing operations.

The voting and multicast came about because measurements showed that the low band noise floor was quite elevated and variable. To provide reliable communications required this type network.

The SNV-12 voters have ability to buffer audio for several hundred milliseconds. This was used to the advantage of allowing the mobile radio to scan, receive carrier and decode tone squelch before repeat audio was presented at the transmitter. In this way, mobile receivers would not experience truncated audio.

It has been a while since I left that project, but at one time the prospect of adding VHF vehicular repeaters and VHF repeater sites to the system was being considered.

Low band portable radios are very limited in range due to antenna deficiencies and noise floor.

A low band system is not for the faint at heart or those on a limited budget.
 
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GlobalNorth

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Considering how few VHF low band licensees still exist in my state and that there are itinerant frequencies available, I've considered getting a license for some portable radios to use when out in remote areas for 4wd exploration. No high power base stations, repeaters, etc. It may not be practical, but 1 watt digital 900 MHz radios won't work in the boonies.

Subscribed to see how it works out for the OP.
 

RFI-EMI-GUY

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Yes;
There are three itinerant frequencies available. As with all low band, they are normal wide band FM channels despite the fact that some licensees have licensed narrow band in error.

27.49 Base or Mobile 10.
35.04 Base or Mobile 10.
43.04 Base or mobile 17.

(10) This frequency will be assigned only to stations used in itinerant operations, except within 56 km (35 miles) of Detroit, Mich., where it may be assigned for either itinerant or permanent area operations (i.e., general use).

(17) This frequency will be assigned only to stations used in itinerant operations.

You might want to use high power vehicular radios and use cross band to VHF or UHF portable radios via Pyramid SVR200 repeaters. They are available cheaply on e-bay.


Considering how few VHF low band licensees still exist in my state and that there are itinerant frequencies available, I've considered getting a license for some portable radios to use when out in remote areas for 4wd exploration. No high power base stations, repeaters, etc. It may not be practical, but 1 watt digital 900 MHz radios won't work in the boonies.

Subscribed to see how it works out for the OP.
 

DeoVindice

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You might want to use high power vehicular radios and use cross band to VHF or UHF portable radios via Pyramid SVR200 repeaters. They are available cheaply on e-bay.
The alignment on those Pyramid units is rather daunting, otherwise I'd be all over them.

Low band portable radios are very limited in range due to antenna deficiencies and noise floor.
This may be an unusual experience, but I was getting very similar performance between UHF and low band portables in a built-up residental area. The reduced path loss almost totally offset the inefficient antenna. It was around a mile and a half on UHF, and a mile and a quarter on low band. This was only using a tuned KRA-21 on a TK-190.
 

W8UU

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I ran portable operation on 48.96 MHz with some Motorola HT-1000s and rubber duck antennas a few years back. Not bad on range and the antenna was just a couple of inches longer than VHF. I wouldn't recommend portable use on any low band frequency below 46 MHz unless you wanna go old school and use the telescoping whip antennas. Still, they're not optimal performers.
 

W8UU

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It is not just the antenna, it's the ground plane. The small hand held radios don't provide much in the way of a counterpoise for the low band VHF stuff.
Correct. But you get a better ground plane at 48 MHz than you do at 31 MHz.
 

70cutlass442

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The SNV-12 voters have ability to buffer audio for several hundred milliseconds. This was used to the advantage of allowing the mobile radio to scan, receive carrier and decode tone squelch before repeat audio was presented at the transmitter. In this way, mobile receivers would not experience truncated audio.

It has been a while since I left that project, but at one time the prospect of adding VHF vehicular repeaters and VHF repeater sites to the system was being considered.

Low band portable radios are very limited in range due to antenna deficiencies and noise floor.

A low band system is not for the faint at heart or those on a limited budget.
So would the mobile units do the scanning and signal sampling? I have seen ICOM do this but am unfamiliar with other radios doing this. I have a customer that would benefit from this.


Good luck finding radios (base stations) these days.

Very few companies are making them now.
I have a few Maratracs around which can be used as a TX radio.
 

RFI-EMI-GUY

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The alignment on those Pyramid units is rather daunting, otherwise I'd be all over them.



This may be an unusual experience, but I was getting very similar performance between UHF and low band portables in a built-up residental area. The reduced path loss almost totally offset the inefficient antenna. It was around a mile and a half on UHF, and a mile and a quarter on low band. This was only using a tuned KRA-21 on a TK-190.
The Pyramids are not that bad. It is a repeater with two audio directions that need to be adjusted.

Maratracs were initially used. Non priority scan, with AND squelch logic with the noise squelch set to about 18 dB SINAD.

Portable to portable might be ok. However portable to repeater, at elevated antenna height, the noise floor can be quite high. Our tests showed only a couple miles talk back.
 
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