Tait T800 Series I EPROM Calculator

As I said in an earlier post, the Tait PGM800 software will not let you program a T800-10 with 10kHz channel increments.  I need the 10 kHz channel spacing to program up the frequency assigned to me by the ORRC.  After I figured out all the nuances of the bytes that needed to be laid out on the PROM, I wrote a Perl program to calculate the bytes that needed to be pasted into your favorite hex editor.  I also posted this to the Tait_Radios Yahoo! group.  Hopefully someone finds this useful.


#!/usr/bin/perl


use strict;
use Math::Round;


#  SET PARAMETERS HERE


#  Reference clock frequency in MHz
#  6.4 for T855-10
#  0.2 for T857-10
my $refClock = 12.8;


#  Channel step size in MHz
my $channelStep = 0.01;


#  1 for a transmitter, 0 for a receiver.
my $transmitter = 0;


#  Frequencies you want to get lines for
my @frequencies = (
                     439.900,
                     439.910,
                     439.920,
                     439.930,
                     439.940,
                     439.950,
                     439.960,
                     439.970,
                     439.980,
                     439.990,
                  );


#####  NO USER SERVICABLE PARTS BELOW HERE #####


my $scalingFactor = 64 * $channelStep;


foreach my $frequency (@frequencies) {
  my $target = $frequency;


  if ($transmitter == 0) {
    $target -= 45;
  }


  my $M = int($target / $scalingFactor);
  $target -= $M * $scalingFactor;


  my $A = round($target / $channelStep);


  my $R = $refClock / ($channelStep * 2);


  #  Hex Conversion
  my $MHex = $M << 2;


  #  Convert into a proper string
  printf("0%01X 0%01X 0%01X ", $MHex & 0x00F, ($MHex >> 4) & 0x00F, ($MHex >>8) & 0x00F);
  printf("0%01X 0%01X ", $A & 0x0F, $A >> 4);
  printf("0%01X 0%01X 0%01X ", $R & 0x00F, ($R >> 4) & 0x00F, ($R >>8) & 0x00F);
  printf("\t%.3d\t%.2d\t%.3f ", $M, $A, $frequency);
  if($transmitter == 1) {
    print "TX USING ";
  } else {
    print "RX USING ";
  }


  printf("%d KHZ STEPS", $channelStep * 1000);
  print "\n";
}

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.

What's the Frequency Kenneth?

Good News Everyone!  I went up to La Pine on Sunday to attend the operations meeting of the Oregon Regional Relay Council, the coordination authority for Oregon.  During the meeting the application for coordination was considered, and we were assigned the 434.910/439.910 frequency pair.  This is in the "GMSK Repeater" section of the bandplan, and there's really nobody else up there right now.  It turns out that ORRC allocated this spectrum not knowing that the Icom repeaters can't actually tune to this pair.  This isn't a problem with the KF7LDG repeater because we'll be using standard FM gear that's more frequency agile.  The really good part about being on that pair is that we shouldn't be disturbing anyone on FM, and they shouldn't really be effecting us all that much.  Thanks to Daron and Dan of the ORRC for their help and understanding during the process.

Receive Antenna on the Top Tower Section

In other news, the receive antenna arrived on Friday.  As I said before, it's a Telewave ANT450-D3.  It'll be mounted at the very top of the tower mostly because I'm more worried about hearing folks than being about to get to them with the transmitter.  Note that if you're mounting these folded dipoles on a smaller tower like the Rohn 25G, you'll need a shim kit, which is part number ANTS420.  Note that the description says (2) on it, but you'll need one kit for each dipole.  The (2) refers to the fact that a pair of them shims up a single dipole.

I tested them up in ghetto style by bringing the top tower section over to the trunk of my car and hooking the dipoles up to my ID-880H mobile.  I was able to hit FM repeaters as far away as Eugene and Salem, so I'm thinking the antennas should be plenty good for the purpose.  When all of the tower sections get painted, I'll be mounting the transmit antenna on its tower section.

And Then the Government Intervened

Well, things were going a little too well, and the project was moving along as a good clip.  The hole is completely dug.

Perhaps a little too well.  I was doing some extensive reading on tower erection and care and realized that I'd better check the county building regulations to see if I needed a building permit for the tower.  It turns out in Benton County that anything that's over 10' tall requires a building permit.  I could have just proceeded with the project and hoped nobody would notice.  I decided to take the high road instead and notify the proper authorities so it could be done right.  That way I wouldn't have to tear it down later when someone noticed it didn't have a permit.

So, since the airport is outside of the City of Corvallis limits, I enquired at the Benton County building department, and they informed me that they had an intergovernmental agreement with the City such that I would have to get a permit from the City of Corvallis.  This was something I was hoping to avoid.

I journeyed to the City's planning department to figure out what the deal was, and was told that I would have to get approval from the airport manager before they would do anything.  I drove out to City of Corvallis Public Works where the airport manager lives and had a productive conversation with him.  He has been the most helpful and painless piece of this process so far.

Then I contacted the person in the city planning department.  To their credit they have been responsive and helpful via e-mail.  The major problem right now is that they have decided that the stock Rohn drawings aren't enough to get a building permit.  I have to now go to a local civil engineer and get a set of plans in triplicate.  This promises to be costly.

The second problem they have is that the tower may be too close to the property line.  They're concerned that if the tower were to fall it would fall across the property line.  I could understand their concern if this were in the city limits, or if we had any significant neighbors.  The truth of the matter is that on both sides that matter, there is farmland, and there would be no impact if the tower were to fall.

So, we're currently derailed with governmental building requirements.  I'm hoping that I can get through all of the red tape before monsoon season starts here in Oregon and construction will be problematic.