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Author Topic: Lectro Duet - Multiple Transmitters  (Read 423 times)

Neil White

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Lectro Duet - Multiple Transmitters
« on: February 08, 2021, 07:29:06 AM »

Does anyone have experience of using Lectro Duet IFB systems across a wide area, that might require multiple transmit sites on the same frequency? Is the belt pack able to roam between coverage from multiple transmitters on the same frequency? What happens in overlapping coverage areas?

Previously been using Wisycom MTK952 linked by fibre for multiple transmits but have been asked to look at options that would provide increased security to stop anyone listening in to IFB frequencies.
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Henry Cohen

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Re: Lectro Duet - Multiple Transmitters
« Reply #1 on: February 08, 2021, 11:42:29 AM »

Does anyone have experience of using Lectro Duet IFB systems across a wide area, that might require multiple transmit sites on the same frequency? Is the belt pack able to roam between coverage from multiple transmitters on the same frequency? What happens in overlapping coverage areas?

Previously been using Wisycom MTK952 linked by fibre for multiple transmits but have been asked to look at options that would provide increased security to stop anyone listening in to IFB frequencies.

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Henry Cohen

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Tim Hite

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Re: Lectro Duet - Multiple Transmitters
« Reply #2 on: February 08, 2021, 04:38:48 PM »

If you're just trying to cover a longer distance, I've pieced together a solution from off the shelf components to get up to about a mile of range out of a Duet using an outboard amplifier.

Can take you up (in steps) to well over +24dBm output (about 250mW), which is the legal limit for Part 74 license holders.

There are also multiple zone antenna splitters that can help extend your range with a single TX.
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Henry Cohen

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Re: Lectro Duet - Multiple Transmitters
« Reply #3 on: February 09, 2021, 04:00:43 PM »

Does anyone have experience of using Lectro Duet IFB systems across a wide area, that might require multiple transmit sites on the same frequency? Is the belt pack able to roam between coverage from multiple transmitters on the same frequency? What happens in overlapping coverage areas?

Previously been using Wisycom MTK952 linked by fibre for multiple transmits but have been asked to look at options that would provide increased security to stop anyone listening in to IFB frequencies.

There's no way for any receiver to "roam" among transmitters on the same frequency since, as far as the receiver is concerned, there's only one transmitter (frequency) [that seems unstable]. The proper method of having multiple transmitters on the same frequency to cover a large area is simulcast, and that requires some manner in which to sync the transmitters' analog oscillators or digital clocks so they are all on the same exact frequency +/- 1Hz. (These days that's accomplished using either GPS, NTP or PTP in LMR deployments.) AFAIK, there's no provision for external clock sync in the Duets, unless the LAN connection supports NTP or PTP, specifically for the clocking of the frequency synthesis, or there might be a pick off point on the microprocessor bus (Karl?).

Without simulcast, simply having multiple transmitters on the same frequency can be problematic without carefully planning out coverage zones so that overlapping areas, or areas completely devoid of coverage, are identified and minimized. Unlike the "wispies" or ticking sounds of analog receivers detecting multiple co-channel transmitters, digital systems will mute once BER or FER exceeds threshold due to the co-channel interference.

You should be able to employ the same fiber infrastructure you're using for the Wisycom, presuming it's gain structured correctly and the system noise level is at least 20-25 dB below the Duet's received signal level. Conversely, if you're a Part 74 licensee, you can always attempt a higher gain antenna mounted high up and/or you can use an amplifier in order to achieve coverage of your performance area, but RF power can not exceed +24dBm into the antenna coax. Insure the amplifier is very linear, with a very high IP3.
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Henry Cohen

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Re: Lectro Duet - Multiple Transmitters
« Reply #3 on: February 09, 2021, 04:00:43 PM »


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