Wednesday, June 20, 2012

The unfortunate & epic saga of the perfect military radio

The long awaited but ultimately unwanted GMR radio
As my day job starts to include more long term projects & project management I was particularly intrigued by an article in The article is, "How to blow $6 billion on a tech project", although the title may be more inflammatory than technically accurate.

The article covers the 15 year development of an advanced & unified military radio communications system that suffered from multiple issues including scope-creep & a rapidly changing underlying technology.

If you are involved with a group that is working to develop a product or service you'll really get something from this article. If you interested in radio systems, military or otherwise, you'll find this interesting as well.

Its hard to image the frustration people suffer when contributing to a project that is mismanaged unless you have been there yourself. I hate to think of the wasted effort that resulted when people found out How to blow $6 billion on a tech project

Monday, June 4, 2012

The Johnson 275W Matchbox Antenna Tuner

I had purchased a Johnson Matchbox from an estate a while back & decided that while I was home with the flu I would open it up and check on its condition.

The Johnson Matchbox is found most commonly in two versions, the smaller "275W" unit and the larger Kilowatt Matchbox. Why did I use quotation marks around 275W? Well, these units were manufactured back in the good old days when men were men and transmitting voice meant using AM, not single side band. The conservative rating of 275W of AM translates into roughly 800W of peak SSB  (Not really but close enough so you get the idea)

Unlike many who own a Matchbox I was hoping to keep it 100% original and that it would contain all its original components, including the antenna change-over relay and wiring for the high-impedance receiver antenna connections. I plan to use this Johnson Matchbox with a Heathkit AT-1 transmitter and Hallicrafters SX-25 receiver so the inclusion of an antenna change over relay and 300 Ohm receiver connections will make life MUCH easier. Something I didn't realize until I had the unit apart (There are a LOT of screws holding this thing together) is that there is also a receiver control contact on the relay to break HT and mute the receiver during transmit which will work with my SX-25.

An initial inspection showed that the only modification was a small piece of plastic wedged into the relay contacts that held the relay in the transmit position. It was easily removed and the relay coil and contacts tested for continuity. The contacts seem a bit dirty which, from the little I have read online, seems to be a common problem.

Once the relay contacts and band-switch are cleaned I will button the unit back up and connect it to the loop antenna I have recently run around the eaves of the house. The loop has been a huge improvement to the long-wire and magnetic antennas I have run in the past, at least as far as reception goes ... but that is a topic for another post.