I made it to the monthly Hams In The Park (HITP) event this afternoon, though I was in a separate lot from where the action was taking place. Instead of the picnic area near the beach, I settled in at the lot across from the History Center where dog-walkers tend to congregate. There was a nice concrete apron where I could set up my tripod, though no seating.
That's where I set up an RF-only APRS station. And the dog-walkers stopped to ask what I was doing. Since I like dogs, it was a nice outreach opportunity.
Aside from the telescoping tripod, I had a dual-band mobile whip mounted on the tripod. Also, a 2M monoband HT and a Mobilinkd TNC2, along with some RG-8X coaxial cable. Last, I had an old Android smartphone that had no cell plan running APRSDroid that connected to the TNC over BT. I wish I had taken a picture.
Before I left home for the park, I configured the Mobilinkd to work with the smartphone by setting the audio levels. To set the transmit audio, I reduced the output RF of the HT to one watt. When I set up the station, I neglected to switch it back to 5W, and it ran that way for an hour.
I was pleasantly surprised to find that one watt was enough for a portable station. My packets were gated every time, either by the Medina W0PZT-1 I-Gate (18 miles away), or by the N0MQL-1 gateway in Centerville (10 miles away). I think the U of M W0YC-5 gateway (8 miles away) even got one.
When I switched the RF output to 5W later, I reached the N0HOY-10 and KF0ZH digipeaters, spreading those packets across the metro. This once again proves that a 5W station can work pretty well in the metro.
The antenna itself was nothing impressive. It was unity gain on 2M, and its base was about seven feet off the ground. Add 12 feet of feedline loss and the insertion loss of a SMA/SO-239 adapter, and I probably would have done just as well with a stock duck and a "tiger-tail".
This station was never intended to impress, however. It was a proof-of-concept affair to show what could be accomplished with a low-power portable APRS station set up in the field, and to get a clear idea of what the limitations of such a field station would be.
The limitations all seem to focus around the power supply. The TNC2 can run for 48 hours on a full charge, so that wasn't really a limitation. The HT, however, would have probably run out after five hours. This is because I had to leave the squelch open to assure that the beginning of received packets weren't cut off. If I had set the squelch to the lowest setting, I think I could have run the HT for over seven hours. The smartphone battery was another limitation, but that could have been solved with any common 5V USB-connected battery packs. And much of that drain came from the GPS, so if I had a stored position in the phone it wouldn't have mattered. Again, there was no cell connection or cellular internet, and no wi-fi. The primary drains were Bluetooth and GPS, with the display being a negligible factor.
So, in an "EmComm situation", this station would have functioned well -- assuming that gateways and digipeaters still were functioning, of course. Even using one watt, I was able to reach about ten miles with a marginal antenna solution. Virtually anyone could do equally well in a power outage -- or in a situation where the internet is down. Ten miles can cover most of the freeway loop without a digipeater.
Aside from testing the viability of a portable APRS station, I also created an APRS object for the event, originating from my home gateway, KD0TLS-1. As I've noted before, KD0TLS-1 is far from a power-house station. It runs a mere 10W into a shabby ground-plane antenna on my balcony. But it was able to leverage local digipeaters to create an RF-only object for the HITP that even reached Faribault, Paynesville, Rockford, Centerville, and Stacy. And I only used a WIDE2-1 N-path for the object.
This was only my third attempt at creating an APRS object, but I think it was the best. The object was called "HAMSPARK" with the text being "Hams In The Park event".
I used the APRSIS32 software that runs my I-Gate. First, I had to zoom in and center the cross-hairs on the target (Long Lake Regional Park), offsetting it enough that it wouldn't cover up mobile stations at the event. Then I went Configure/Objects/Create to get to the dialogue for objects. For "Group", I used HITP -- but you can use anything, including your callsign. Next, I named the object "HAMSPARK", but I could have named it HAMSINTHEPARK. Next, I set the comment text as "Hams In The Park event", though there was room for more info. Last, I checked the button marked "Via RF" and entered the N-path as WIDE2-1. "Accept" sealed the deal, and the object was transmitted every ten minutes.
Sure enough, the object appeared on aprs.fi almost immediately, and it was marked as originating from my gateway.
In addition, I sent a local bulletin over RF two days before the event, announcing the date, time, and location.
If I did it, you can do it. You don't need to send any of this over RF, either. The -IS is pretty effective. Maybe next month (5/6), someone else can do the promotion on APRS for the event.
I hope to see you there next month. I'll probably move to the popular lot with the cool kids, though.
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