Other SOTA sites: SOTAwatch | SOTA Home | Database | Summits | Video | Photos | Shop | Mapping | FAQs | Facebook | Contact SOTA

X-band repeat . . . poor man's APRS digipeater?

Hello everyone,

I’m wondering if cross-band repeat would work as a way to get a weak APRS signal from a handheld out to the network while activating remote peaks?

Process:

  1. Kenwood TH-D72 handheld (moving with the activator) originates packets on 70 cm.
  2. A mobile unit back at the trailhead picks up the signal.
  3. Mobile unit repeats the packet on 2 M with higher power.
  4. 2 M network picks up the packet.
    Caveat: To avoid causing interference with the 2 M APRS frequency you would have to be listening to 2 M using the second VFO in the handheld. Then you would beacon manually only when the frequency was clear.

Will packets remain intact when repeated cross-band like this? Has anyone tried it?

It’s a given that the more elegant option would probably be to use a Tiny Trak or an SCS Tracker connected to the mobile unit to act as a digipeater at the trailhead. However, if you didn’t have one of those TNCs would cross-band repeat do the job?
Thanks everyone,
N6BSC

Done a bit of 70cm x band from my vx8 back to my truck with an old kenwood dual bander on aprs vhf repeater. The work shed had a good line of site to the digi and my vx8 on 70cm packet frequency 439.100 did the rest on aprs/ tractor mobile around the farm. Bit of a novelty thing that wore off after a while. Had no luck around vk5 on aprs from a hand held into digipeaters so don’t bother with it any more on SOTA hikes. APRS track is an app for a phone that works well but it burns up the battery and leaves you nothing if you need to spot on a summit.
All good fun and part of this great hobby.
regards
Ian CZ …

I used to run an igate in similar faahion. Xband listened on hill top on vhf, transmitted to an igate on 70cm in town. Worked a treat.

If you are on a remote hill and cannot “see” a APRS node from the summit it is unlikely that your mobile at the bottom of the hill would be able to link into the network on VHF either.

A while ago I experimented with APRS in remote locations x-banding from VHF to HF.

(http://www.summits.org.uk/tiki-index.php?page=APRS+Tracking)

Carolyn

1 Like

Interesting thoughts from everyone. I like the idea of gating into HF when in really remote locations. And that’s also a good point about the mobile probably not having enough reach when the top of the summit doesn’t. Also, nice website Carolyn - going to add that to my bookmarks and sift through the data later.

It might be worth trying the following:
Locations on the edge of getting into an iGate:Mount a small yagi on the mobile pointed at the iGate to give additional reach. (Would have to test how well the 2 M yagi receives the 70 cm packets though.)
Really remote places:Gate into HF.

It works as you can see there people who have used such features. There can be some issues that can limit how well it works.

In a normal packet node, you would receive the signal and feed the audio into a TNC and decode the data. That would get sent to another TNC which would convert it back to tones to send to the transmitter. The results is that some marginal signals (weak, noisy, distorted etc.) can still produce audio that decodes. If you simply repeat that then you may introduce more distortions resulting in a signal that can never be decoded. 2x TNC solution is better but more expensive. You can also put some rules in so only your packets are repeated rather than anything heard.

Secondly, the radio doing the repeating needs to be able to unsquelch itsekf quick and get repeating the incoming signal. If it is a bit slow, the initial data received may not get repeated. You can fix that by making the portable signal have a longer TX delay if needed.

However, as Carolyn says, if the car is parked at the bottom of the hill then it’s not too likely to be able to get a signal into the APRS network. So whilst you can probably get a simple audio repeater to operate you may not gain anything. If you go to HF on one side then you really will need a pair of back to back TNCs as HF is done at slower speeds than VHF. 300bps AFSK is one standard but you may find lots of HF APRS stations adopting more modern modulation schemes because the work better. At this point as long as you can be heard by your repeater then you can get your local VHF/UHF APRS packets out via HF.

The question you need to ask is whether the setting up and experimenting with these ideas is the fun and worthwhile or are you trying to get a message through saying “I am at the summit on freq X” i.e. a self spot. If it’s the latter, simply use a smartphone with APRSdroid or some such to send the APRS message and connect that to your HF rig at the summit and send your message then.

If the message being received is more important that the experimenting with a portable repeater etc. then there are other ways much more likely to get the message through. But they probably wont use amateur radio but commercial services that cost money. You need to decide if the message is the purpose (in which case spend money to send it) or the “doing of the experiment” is the purpose and then playing with radios and TNCs etc.

If you have a radio that does x-band repeating already you can try the simple method for not much effort. When I though about it I came to the conclusion that I want to get the spot message through rather than play with APRS nodes so I spent money on a commercial service. I still had “fun” (no I didn’t) writing the software to make it work. But now it boils down to a spot costing 40p to send. The fun comes from walking in the countryside and being the DX when I set up the SOTA station.

MM0FMF,

I think you make some pretty good points. You’re right about always having to consider the cost-benefit analysis. It is very easy for a “simple” idea to spiral out of control and end up yielding very little in the way of returns. It is (almost) always fun to experiment, but we always have to keep the results, or lack thereof, in mind.

The main region where I’m looking for more range is in the California deserts where I am doing more and more hiking. The deeper areas around Death Valley especially offer very remote locations, no digipeaters, and often not even any cell service. Cross-band repeating probably won’t help there at all, now that I think about it.

I do like the idea that was raised by a few people to use HF APRS to get a signal out. With a bit of research I’ll bet that I could use a Tiny Trak or SCS tracker at the trailhead to gate vhf packets over to 30 M HF. I’m already working on getting HF APRS set up in my vehicle just for those remote locations, so I think I’ll look into gating between VHF and HF (with appropriate safeguards to be sure only my packets are gated) a way to increase the range.

Thanks to everyone for the feedback.

N6BSC, please update us as you work out a solution to getting spotted in areas with no cell coverage. I’m interested in the topic.

Kevin AC2KL

“I do like the idea that was raised by a few people to use HF APRS to get a signal out. With a bit of research I’ll bet that I could use a Tiny Trak or SCS tracker at the trailhead to gate vhf packets over to 30 M HF. I’m already working on getting HF APRS set up in my vehicle just for those remote locations, so I think I’ll look into gating between VHF and HF (with appropriate safeguards to be sure only my packets are gated) a way to increase the range.”

If you re-read my link I have explained in detail how setup and configure a working VHF>HF APRS system!

The 2 main reasons I stopped using it was that very few people gave feedback on its usefulness (and as Andy has pointed out its not ever going to replace commercial communication equipment) and often once I get something working reliably I get bored and move onto a new challenge.

Carolyn

I have found that when I am on a remote Northern California summit with no cell coverage I am able to post via APRS to SOTA with no problem. I use a Kenwood TH-72D with just the rubber duck antenna. I sometimes have to turn the APRS channel volume down or off because there is so much activity it gets annoying! It is not unusual to see a position report from a station 150 miles away direct. Altitude is your friend on VHF. I am going to make a twinlead J-pole to hang on my pole for better coverage on 2 Meter FM after I have my fill of HF contacts. Or better yet a folding Yagi to try 2M CW since I have it in my KX3. APRS coverage in this area seems so good that I think it counterproductive to try XBAND for it.