The Good, the Bad, and the Ugly.

Lots of things happening this week with the project.  After a flurry of e-mails between the Benton County planning department, the City of Corvallis planning department and I, I have gotten their approval for the land use issues.  Since it's amateur radio related, they're going to consider it an ancillary use, and it won't need a conditional use permit.  The City also talked to the airport manager, and since he didn't have an issue with it, the City is going to allow it under the Airport Industrial Park Master Plan.  I'd like to thank Dan Mason, the Corvallis Municipal Airport Manager; Kevin Russell from the City of Corvallis Development Services; Chris Bentley from Benton County Community Development; and Bill Clemens of  the City of Corvallis Building Department.  My advice to other hams after going through this process is to be patient, persistent, and helpful with the planning officials.  Explain to them the purposes and goals of the amateur radio service, and help them understand that what you're trying to do isn't to make a lot of cash.  It was particularly important to Benton County that I pointed out that the FCC regulations and federal statutes prohibit pecuniary gain.

This just leaves getting a building permit for the tower.  I had some trouble finding a professional engineer to draw up plans, but after finding the ARRL's Volunteer Consulting Engineer program I found Hank Lonberg.  Hank has looked at my crude drawings and some pictures and given me an estimate of $750 for the required engineered plans.  This is fairly expensive, but I guess it's the price of doing things right.  After I get the drawings, I can finish the permitting process and move forward with tower construction.

I finally got all of the tower segments painted white, and I got to work on getting the antennas attached to the segments.  The receive antenna was no problem and I got it attached a while ago.  The transmit antenna is another story.  The problem is that the mounting brackets for the dipoles are rather large and beefy.  In contrast, the Rohn 25G is rather small.  You need shims to make them fit.  The issue here is the cross-braces on the Rohn 25G tower.  It blocks the clams in places so that you can't mount them.  This is in the area where the horizontal cross-brace bends to go diagonally.  The problem is that the spacing between the dipoles is supposed to be 19.375".  It's entirely possible to make this spacing work with three dipoles, but when you move to four, it's pretty much impossible to get the spacing right.  I ended up getting fairly close, and one of the dipoles is a little less than an inch out of place.  I think what I may have to do eventually is get a mast of galvanized steel pole and clamp it to the tower leg instead of directly mounting it.  Unfortunately, it took a lot of time and frustration trying to get things to work out correctly.

I hooked the top two tower pieces together, and with a little white lithium grease, they went together perfectly.  I then leaned them up against the building to do some rough testing.

I mainly got the antennas going because I finally got the the RF gear from the guy in Idaho.  I now have the T800 gear installed in the rack and hooked to the antennas.  I attached some Anderson Power Poles to integrate with the power system in the rack.  I also attached 6-pin mini-DIN connectors to the headers on the back of the repeater.  The connections are fairly straight forward with the exception of the audio connections.  The cool thing about the Tait is that it has 600 ohm transformers on the inputs and outputs of the repeater for isolation.  Unfortunately, Satoshi's Node Adapter has all of the stuff referenced to ground.  That means that you have to tie one leg of all the transformers together.  Hopefully this won't cause any major issues.

The other trick with the interface between the Tait and the Node Adapter is making the COR work correctly.  The COR is held high when there is no signal, and brought low when the squelch opens.  This is opposite of the "default" configuration of the node adapter.  The settings I used were SW1: ON  SW2: OFF and SW3: 1-2.  With this configuration the COR light on the node adapter lights up when the gate LED activates on the Tait receiver.  This should make things work okay.

The only other problem with the Tait gear I have right now is that I have the T855-10 model.  This is the gear designed for 12.5 kHz channel spacing.  The filters are a bit of an issue, but the real problem is that the Tait programming software will not let you program channels that are not divisible by 12.5kHz.  The ORRC assigned me 434.910 as the transmit frequency and 439.910 for the receive frequency.  These aren't divisible by 12.5 kHz and can't be programmed.  Luckily, there are a few messages on the Tait Yahoo group about exactly how the PROM is set up, and which bits need to be set.  It's a lot of screwy math, and it's taken me a while, but I understand how things need to be set up.  I just have to program the bytes manually in the file, and I can make it work okay.  The thread on the Tait group starts here.  My EPROM programmer hasn't arrived yet, so I have to wait to try it out.

So, we're almost ready for on-air testing and evaluation.  I don't have the duplexer yet, so I'm not sure if I'm ready to go full duplex yet.  There's quite a bit of isolation between the antennas just because of the fact that they're spaced a ways from one another, but I don't think it's going to be enough to work well.  After that, it's just dealing with tower issues.