This project started about seven months ago when Thom W8TAM sold me a Kenwood TK-790 radio (ex-BNSF railroad) at the Chelsea MI swap. The 790 is very sturdy and heavy and looks like it would put up a fair fight against a locomotive. The radio was already programmed by W8TAM for local Ann Arbor area repeaters, but it was otherwise bare - no power cord, no mic, no speaker, no antenna, no data cable. I put together a complete rig and hauled it to a local park on my bike to operate "bicycle portable", that is to say not operating while mobile but hauling everything on the bike.
Mobilinkd has an excellent writeup about this radio, from Rob Riggs, WX9O, Mobilinkd LLC.
http://www.mobilinkd.com/2020/07/29/the-kenwood-tk-790/
https://nbviewer.org/github/mobilinkd/KenwoodTK-x90/blob/master/Kenwood_TK-790.ipynb
I will refer you to it if you are considering acquiring one. Beware that there are a few pitfalls in getting these set up for amateur use, and some variants that are not ham-friendly. Read before proceeding.
Rob WX9O took a DIY approach to manufacturing a microphone cable, constructing a speaker interface, programming the radio etc. It's a detailed project, and he warns:
It really does not make sense to buy a TK-790, and then go out an buy all of the accessories needed to make it a functional radio.
Yet that is what I did, slowly, with the help of eBay. The power cord is Kenwood KCT-23, with power pole ends that were added at the annual ARROW meeting. The mic is a Kenwood KMC-27 from https://used-radios.com . The speaker is a Kenwood KES-4. My battery is a Bioenno BLF-1215A via Gigaparts which provides the 12A of power that this 45 watt rig wants. I'm using an N9TAX Slim Jim antenna.
First test of the whole setup is at home. With everything plugged in, the indoors antenna across the room and hanging in the window is fine. I'll look for a suitable outdoors mount for some kind of 2m antenna when the weather is warm. On the very first test I didn't have a speaker, so I used another home 2m receiver - an OpenWebRX+ setup in the attic - to tune in.
Some discussion on Mastodon - specifically on mastodon.radio - ensues about 2024 goals, and I volunteer that I want to activate a park with this rig. The multitudes encourage me, so I pack all of these parts carefully into an Ortlieb saddle bag, and head out on my bicycle to Burns Park about half a mile away early in the morning to try everything out.
What did I learn along the way:
If you wear enough layers, you can operate in the cold and damp. Bring some layers for your rig too -- I would not have wanted to turn everything on if it was actually pouring, but by strategically covering everything when it was not in use that worked out pretty well.
The Kenwood parts for this rig are kind of fiddly. The KCT-23 power cord is fine (I put new power pole ends on it) but the connector to the radio itself has the feel of old brittle plastic just waiting to snap after one too many connections. Thom W8TAM modified his rig to have the power poles right on the rig rather than at the end of a cable; that's a worthwhile change to consider.
The KMC-27 mic is also kind of fiddly. It has a weird pogo-pin connector on it, which was used only on this series of radios and none other. Parts are relatively expensive and the 3-d printed adapter from WX9O was out of scope for now. Note that the connector uses a thumb screw to make the connection secure, and I discovered that if you don't screw it in all the way you simply don't make a transmission at all.
The KES-4 speaker? Also fiddly. This has a weird 9-pin plug on it (Molex, I think) with only two pins active, and I'm wondering which time I'm going to tug on it too hard and have the plug assembly come loose. The modification that I saw involves sourcing that plug and then using the two pins to attach a little lead that has a standard mono jack on it, so that you can use ordinary speakers with this.
When I bought the N9TAX antenna, I had it built with what looks like a coat hook attached to the top. That hook was enough to wedge into a crook in a tree in Burns Park helpfully near a picnic table and operate from there. Again, for a next time: it would be useful to have another section of feed line to attach, so that I could get the antenna higher. I've also been looking at arborist throw lines as a way of getting some more elevation into trees.
It's terrific to have a weekday morning 2 meter net to test against. The crew that is on the 800a N8DUY weekday morning roundtable is always welcoming and has tolerated my bicycle mobile and pedestrian mobile testing for some time. They are always happy to hear a good strong signal, whether it's 45 watts into an antenna stuck into a tree, or 50 milliwatts from the top of a parking structure with a clear line-of-sight to the repeater. Thanks to Jim W8STX for organizing this net that's open to all licensed amateurs on 145.15- PL100 out of a repeater just to the west of Ann Arbor.
As to the radio itself, some operating notes.
I guess there's a 5 watt setting on this rig, but I used the 45 watt setting, and signal reports were excellent. It would be worthwhile figuring out how to switch between the two.
Thom W8TAM programmed in all of the Washtenaw County repeaters. I'll want to test all of those one at a time, and I'll also want to test simplex operation. No idea yet if I can do a front-panel addition of more channels.
The signal reports were excellent but my mic gain I guess is kind of low, which either means TALK LOUDER or tweak some gain setting.
Eventually I want to do digital modes on this thing, since there's a 9600 baud serial connector on a DB-25 on the back that brings out a bunch of interesting signals. How long has it been since I've built a serial cable? Again hoping to find someone who has gone before me. On the wish list: APRS, RTTY, and maybe even digital voice with M17.
It's entirely possible that most of the reason my signal reports were good was that my antenna was up a little bit and out of doors. I will be practicing with this antenna and this location and a few other radios to sort out what the best bet is.
Did I mention that this rig is built like a locomotive? That suggests that it's perhaps not the most practical approach for a bicycle (and I wouldn't want to haul it all to the top of a mountain).
Thanks to all who helped out with this adventure. In no exact order:
- W8TAM for propelling me down this path, and for sage advice
- WX9O for keeping very detailed notes on from-scratch rebuild of components
- W8STX and the weekday morning roundtable crew including N8QM, N8FPV, K8WXQ and dozens of others
- N8DUY for the use of the repeater
- the taxpayers of Washtenaw County, who help fund the repeater
- the ARROW club
- M0YNG for keeping mastodon.radio a welcoming place to nerd out about the radio hobby
- toot.bike and #BikeTooter for keeping Mastodon a welcoming place to nerd out about bicycles
- VA7BKW and K4SWL for encouragement
- N9TAX for antenna design and build
- KB6NU for an earlier antenna build session
- KD8WKU and All Hands Active for Repairsday Thursday and antenna repair
- NO5IG for antenna hoisting stories (and why real arborists don't use Baofengs as ballast)
- Sic Transit Cycles for the saddle bags
- Common Cycle for cooperative bicycle repair
- BNSF for buying - and then getting rid of - this TK-790
73 de Ed W8EMV
