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Don Kemp's avatar

A friend of mine ( now a silent key) put a simplex repeater up on 145.510. the antenna was atop of a 450 ft. tower in Columbiana county, Ohio. The coverage was phenomenal. Stations out of local simplex direct range had no problem. Stations who could hear the primary signal could not get a grasp that you had to wait till you heard the second repeated primary signal and screwed everything up. There will be a steep learning curve until the local repeater oriented guys finally figure it out. 73, Don, NN8B

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Steve Stroh N8GNJ's avatar

Don: The best thing about TIME DOMAIN DUPLEX Single Frequency Repeaters is that they're (at least to the ear of us mere humans) Full Duplex, so that irritating and confusion delay waiting for the other person to finish their transmission isn't a factor.

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Paul Elliott's avatar

- QRP Labs SSB using Polar Modulation -

Here is a great youtube presentation by Hans about this. He details the trials and tribulations along the way to finally making it all work:

https://www.youtube.com/watch?v=bsDBcFXgHbY

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Steve Stroh N8GNJ's avatar

Paul - Thanks for that. Will mention that next issue.

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Uncle Milburn's avatar

I've been using https://www.wm7d.net/perl/ulsquery.pl as my lookup for decades.

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Steve Stroh N8GNJ's avatar

Uncle - That's a nice one too. I briefly got sucked into WM7D's links - that's quite the rabbit hole.

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Justin AB3E's avatar

Man the SFR stuff is even more tempting now that I know there is actual repeater hardware that presumably can handle longer-term high duty cycles...

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Steve Stroh N8GNJ's avatar

Justin - Agreed! My mind is still reeling about the potential of TDD SFRs.

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K4HCK Cale's avatar

Kudos to WB2OSZ for trying to implement some organization to the APRS spec. And who else is better positioned to do so? If you've ever watched the output of Direwolf scroll through a terminal window, the lack of clarity around the spec becomes clear. Lots of comments along the lines of "this is probably a message from station X"

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Steve Stroh N8GNJ's avatar

Cale - Agreed! WB2OSZ's work on collecting all the ephemera into a modern APRS specification is, in my opinion, nothing short of heroic.

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Werner OE1WRS's avatar

Tetra uses single frequency repeater in DMO mode, we do have a number of Tetra repeaters in OE land (and other countries) which work on one frequency without duplexer etc. those are even networked so when you talk on one in one city you are also heard on the other repeaters in other cities (or on mountains). Most Tetra terminals can act as repeater….

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Steve Stroh N8GNJ's avatar

Werner - Thanks for that info. Will correct my statement saying that Tetra can't do TDD SFR.

For those, like me who aren't very familiar with TETRA, see https://www.teltronic.es/en/what-is-dmo/

In radio communications, unlike Trunked Mode Operation, TMO, in which the transmissions are made through a TETRA network infrastructure, the DMO, Direct Mode Operation, describes the ability of TETRA radio terminals to communicate among them operating independently from the network, as if they were simple walkie-talkies.

However, the most frequent use of the DMO is to create an extension of the network allowing communications in areas where there isn’t coverage. Through gateways, DMO users can maintain contact with TMO users. In this way, the radios operate like mini base station that can provide service to others that are outside the network.

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