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Repeater vs. Simplex


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ELMER

@W3TDH and @KN3U - Nice seeing you both today for the Tacoma 4th of July parade.

Tom, a thought came to mind after the event. I think we all default to repeater use for public service events whereas for smaller, localized events, might it not be better to go straight for simplex? I’m wondering what you gentlemen think.

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ELMER

The choice of whether to use a repeater or simplex should be based on the situation. It is not a “one size fits all” situation. It is all about size. Simplex is fine for a 5k run in flat terrain with no obstructions. We used to support a 5k run in which half the race course was on level ground and the other half was down a steep hill. We used 2 m simplex on one half of the course and 70 cm simplex on the other, and used a crossband repeater sited at the top of the hill (TM-D710) to link those two frequencies. That worked beautifully — everyone on the flat half of the course could hear each other, and everyone on the downhill side of the course was also within simplex range. The crossband repeater linked these two cohorts into one. That’s a special case, but it might apply to other events.

The problem with the event we supported a few weeks ago is that, between the hilly terrain and buildings, simplex doesn’t work well. And their are no nearby repeaters that provide full coverage of the area. A portable full-duplex (conventional) repeater is what makes the most sense in that situation, and that’s what we need to do next year. 

Crossband repeaters work very well to link two simplex frequencies. They do not work so well when trying to access a distant repeater. For example, consider a situation where you need to set up a station in a hospital or shelter where it is not practical to have an external antenna and you need to reach a distant 2 m repeater.  You might be a ale to set up a mobile rig as a crossband repeater with Band 1 of the mobile rig set to reach the distant repeater and Band 2 set on a 70 cm simplex frequency. You access the crossband repeater from inside the building via 70 cm. The problem is that most crossband repeaters are half-duplex. It won’t retransmit your 70 cm signal until the carrier of the 2 m repeater drops. And if there is a lot of traffic on the repeater, the carrier might not drop for an extended period. You are effectively prevented from breaking in to the conversation. 

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ELMER
Just now, KN3U said:

The choice of whether to use a repeater or simplex should be based on the situation. It is not a “one size fits all” situation. It is all about size. Simplex is fine for a 5k run in flat terrain with no obstructions. We used to support a 5k run in which half the race course was on level ground and the other half was down a steep hill. We used 2 m simplex on one half of the course and 70 cm simplex on the other, and used a crossband repeater sited at the top of the hill (TM-D710) to link those two frequencies. That worked beautifully — everyone on the flat half of the course could hear each other, and everyone on the downhill side of the course was also within simplex range. The crossband repeater linked these two cohorts into one. That’s a special case, but it might apply to other events.

The problem with the event we supported a few weeks ago is that, between the hilly terrain and buildings, simplex doesn’t work well. And their are no nearby repeaters that provide full coverage of the area. A portable full-duplex (conventional) repeater is what makes the most sense in that situation, and that’s what we need to do next year. 

Crossband repeaters work very well to link two simplex frequencies. They do not work so well when trying to access a distant repeater. For example, consider a situation where you need to set up a station in a hospital or shelter where it is not practical to have an external antenna and you need to reach a distant 2 m repeater.  You might be a ale to set up a mobile rig as a crossband repeater with Band 1 of the mobile rig set to reach the distant repeater and Band 2 set on a 70 cm simplex frequency. You access the crossband repeater from inside the building via 70 cm. The problem is that most crossband repeaters are half-duplex. It won’t retransmit your 70 cm signal until the carrier of the 2 m repeater drops. And if there is a lot of traffic on the repeater, the carrier might not drop for an extended period. You are effectively prevented from breaking in to the conversation. 

As always, great wisdom from @KN3U 👍

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