A Situation Repeated Around the Country
Representative coverage difference of an analog system. 25 kHz coverage had been available throughout the entire colored area. Coverage that remained after narrowbanding to 12.5 kHz is red, “lost” coverage shown in green.
Communications Managers have had to deal with a rash of user talk-in complaints ever since their analog LMR systems were narrowbanded from 25 kHz to 12.5 kHz. Areas that had been marginal are now “dead” leaving portables completely unable to talk back.
Narrowbanding created significant talk-in problems for anyone dealing with one of these situations:
- Analog systems in the VHF-Hi and UHF bands that already experienced marginal coverage areas for their wideband portables. This is particularly prevalent if sites were originally selected with wideband mobile coverage in mind (with 50 watts of talkback, not the 5 watts of a portable).
- Narrowbanding eliminated coverage where it had been marginal, while some areas that had previously enjoyed clear communications have become marginal and noisy.
- Radio systems whose geography expanded over time due to consolidation or annexation, creating new outlying areas with marginal coverage.
- Systems facing more rigorous in-building communications coverage expectations. Cell phones & Wi-Fi provide coverage practically “everywhere” – raising similar expectations among LMR users. Some radio users may now complain if they can’t also enjoy universal coverage. This situation was further exacerbated by the coverage reduction caused by narrowbanding.
There is a Solution – Receiver Voting
Lost talk-in coverage can be restored and marginal coverage transformed to excellent through the
Typical Installation – Four Channel Repeater System with four voters (in upper left). Each channel has seven voting receivers – the local receiver plus six remote receiver sites to ensure excellent talk back throughout the desired coverage area. Photo courtesy of Steve Dubberstein of Communications Service
implementation of a receiver voting system. If the radio system already has receiver voting, additional receive sites can be installed to cover newly marginal areas as well as those now completely lacking talk-in capability.
In contrast to a repeater-only radio system, a voted system makes use of multiple voting receivers strategically placed throughout the desired coverage area. Whenever a field transmission is made, the voter gets receive audio from every voting receiver that picked up the transmission. The voter continuously selects the best of these signals, which it passes on to the repeater and/or dispatcher. This expands the talk-in coverage area to wherever a portable can reach one of the voting receivers.
Note also that a voting system can also allow the placement of additional transmitters in remote areas for increased “talk-out.”
SNV-12 Analog Receiver Voter. The unit shown has a full complement of 12 SVM-2 Site Voter Modules. As many as three chassis can be daisy-chained together, allowing a voted channel with up to 36 voting receiver sites!
The Essential Facts
- Narrowbanding from 25 kHz channels down to 12.5 kHz caused at least as much coverage area shrinkage as would a 25 kHz channel experiencing a 3dB power decrease (power cut in half). Plus – keep in mind that this is the best case; actual measured results are often closer to 6 dB!
- After narrowbanding, LMR towers no longer talk out (transmit) as far as they did prior. This is minor compared to the fact that narrowbanded portables are no longer able to be heard at all from some areas where 25 kHz portables had been at least marginal.
- Fortunately, you have the cost-effective option of using analog receiver voting to restore lost coverage and remove the noisy audio problem!
- Sometime way down the road (2030? 2035?) the FCC will mandate 6.25 kHz channel equivalent for VHF & UHF. The change to 6.25 can ONLY be accomplished by migrating to digital.
- The FCC has stated that this migration will be mandated only after municipalities realize the “economic value” out of the recent migration to 12.5. That’s why the next deadline is far off in the distant future. Considering the rapid changes in technology, it’s prudent to retain and improve what you have while we all wait to see what the future of communications will hold. Analog Receiver Voting is an excellent and inexpensive tool to make the most out of your current investment in analog LMR.
- Analog radio is not going away anytime soon. In June 2014 an Urgent Communications article covered Thurston County’s “new” analog system and Mission Critical Communications Transmissions had a lead article about analog’s continuing value.
The SNV-12 Remains the Premier Analog Voter
JPS released the SNV-12 in 1998 and it quickly became the industry-leading analog receiver voter (also called a voter comparator). The modular SNV-12 applied what was then the relatively “new art” of real-time digital signal processing to improve upon the received signal quality measurement previously performed by analog circuits. Superior voting capability was not the only advantage of the digital approach – also key were the SNV-12’s ability to offer a wide array of user-configurable options to optimize the overall communications system.
This introduction was followed by multiple no-charge software upgrades and backwards-compatible module hardware improvements, which together gave the current unit the flexibility to deal with almost any system complication that you are likely to experience.
In 2007 IP connectivity was added to the SNV-12 allowing many new features. Among them are the ability to monitor voted audio and a web browser interface to remotely control all basic functions and obtain statistics on each voting receiver site.
Along with its ability to select and pass on the cleanest received audio, the SNV-12’s feature set includes a wide array of transmit functions. These include automatic and manual transmit steering, and the ability to have multiple transmitters on a single channel, with a set of voting receivers groups around each transmitter.
SNV-12 Features Technicians Love
SNV-12 Capabilities Communications Managers Appreciate
- Field proven, over 5000 channels in service
- You can use a browser to log in (password protected) to check system stats, and disable a problem site remotely if necessary. The CPM-3 (with IP interface) came out in 2007 and it can be inexpensively added to most fielded SNV-12s – contact JPS for assistance if voter shelves were purchased pre-2000
- When expanding, you can simply add more channels (or sites) identical to the installed base, no new hardware to spare or learn how to configure
- Basic operations such as Force Vote or Site Disable can be performed from the front panel; no computer is required
- Automatic Fault Timeout removes RX site “frozen” by stuck transmitter, keeping the channel available for other users
Summing It All Up
Talk-in problems were created when analog systems were narrowbanded. Mission critical communications demand the ability of officers in the field to communicate when necessary. Receiver voting can improve talk-in with maximum return on your investment – far less expensive than a major infrastructure build out to add channels or a forklift overall radio system change.
The Main Take-Aways:
- Some channels that weren’t voted may now require it.
- Systems that already employed voting may now need more voting receiver sites. In general, an analog voted channel may need 15-25% more sites after being narrowbanded than it required when wideband – to simply achieve the same coverage and signal quality previously enjoyed.
- Help your customers improve their talk in coverage with new SNV-12s or by adding more voting receiver sites to your existing system!
For more information on the SNV-12 Voter