Sunday, 22 January 2017

FTM-100D Dual Receive Function

Many amateur radios that have multiple "Bands" such as Band A and Band B have multiple receivers built in. This allows each band to receive a different frequency and share a single transmitter. This makes dual mode operations such as APRS on Band A and half duplex voice operation on Band B quite easy to do. Some, such as the Kenwood TH-D7 have two transmitters allowing them to do full duplex. It appears (I have to admit I'm not fully familiar with the radio yet) that Yaesu built the FTM-100D with only one receiver. At first this seems like a limitation, but modern digital receivers can switch frequency very quickly simulating more than one receiver. In this post I will talk about using this capability to operate APRS and work the repeater at the same time. The procedure could be used to do something simpler as well, such as work one repeater and monitor another.

If you are going to use this procedure to work APRS you should have APRS configured on your radio before you proceed. You can use this post to get started.

The Dual Receive Function utilises the Band Home memory and any other frequency either from memory or using the VFO. So the first step is to program the repeater into the Home memory for the Band you are going to use, I will use Band A but you can use either A or B. Setting the Home memory frequency is covered on page 54 of the manual but the steps are:
  1. Switch to VFO mode and Band A.
  2. Tune in the frequency you want, and set up any other operating settings you want (PL tones, etc).
  3. Press and hold V/M MW for over one second. The Memory Write screen appears.
  4. Rotate the dial to select Home.
  5. Press DISP Setup. The overwrite confirmation screen appears.
  6. Rotate the dial to select OK, and press DISP Setup.
Now you should tune in the APRS channel. If you have programmed it into a memory location for Band A you can enter Memory Mode rotate the dial to select that memory, if not you can enter VFO Mode and enter the frequency manually. Now press the A/B DM button for more than one second. The band display will change from MA if you are using a memory location or just A if you are using the VFO to DA indicating you are in Dual Receive mode. Periodically (every 5 seconds by default) the receiver will quickly switch to the Home frequency to see if there is any activity. Dual Receive mode is covered starting on page 70 of the manual, including how to change the 5 seconds.

One thing to be aware of. When using this for APRS beacons will be transmitted when it is time as determined by the APRS software and the receiver doesn't detect activity regardless of what frequency the unit is actually tuned to. If you get involved in a QSO you may end up transmitting a beacon on the repeater frequency. Not the end of the world, but also maybe something that you don't want to do. An easy way to prevent this is to have the Home frequency stored in a memory location in the other Band (Band B) and have that Band set up to work the repeater. Then by switching to Band B for the QSO the APRS and Dual Receive operations will be suspended until you switch back to Band A.

Another is that if you use APRS Muting from page 59 of the radio APRS manual you won't be able to hear the activity on the home frequency. This is because this is APRS operating band mute and all activity on that Band A or B will be muted. I think we are better off using the voice alert procedure from anyway.

This may seem a little complicated, but I've used this to operate APRS and have had QSOs with a couple of people and it is easy to do once you have practised a bit. So if you want to operate APRS without dedicating the radio to that, or just want to monitor one repeater while you work another give this a try.

This YouTube video may also help although this video shows setting the "APRS" frequency as the Home station, but I don't think that is the base way to do it.


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