An APRS Digipeater.
Christopher Greenhalgh, N8WCT
2615 Blacklick Eastern Rd. NW.
Baltimore, OH 43105
Justin Munger, W1IX
RADIO: Motorola Spectra w/A5 head, 110 watts
POWER: Astron RS-35M with Optima Yellow Top battery
TNC: Kantronics KPC-3+, 128k SRAM, Rev. 9.1
FILTER: DCI -145-2H, 2MHz, 4-pole bandpass filter
ANTENNA: Comet GP-9, 8.5db gain, 17.75’ tall
FEED LINE: 45' Andrews 7/8" Heliax LDF5-50A hard line
COMPUTER: Dell Optiplex SX 280 w/broadband Ethernet connection
SOFTWARE: UI-View32 ver. 2.03 (I-Gate out)/PM Streets 8.0/UltraVNC
GRD. ELEVATION: 723' above sea level
STRUCTURE HT.: 260' above ground level
ANT/MAST HT.: 23' above structure height
N8WCT-9: Maroon Ford ranger
N8WCT-15: Red BMW 330iC Cabrio
The BBS (-3), Sysop (-5), and my home mailbox (-6) are for standard RF packet connect requests. Neither support APRS messaging.
the early days of APRS, there were really only two high profile digipeaters…my station in Hilliard, and KA8ZNY-4 (now K8GPS-4)
near Canal Winchester. When I moved from Hilliard in 1996, coverage was very
weak. Since I moved into an “antenna restricted” division, and since I worked
at OSU, I began to think about placing a digipeater
on top of one of the twin towers by the
I found that you could hook your TNC directly to a 9600 modem (via null cable), and you could dial in, and once connected, tell your home software that the modem port was the TNC port. This was really slick, because I could run the APRS software at home, with the benefit of having the high profile antenna. Basically, it was an early “remote desk top”.
However, to achieve this, I needed a phone line at the tower. Luckily, I managed to convince the Universities telecom unit, to donate a line, and my plan was coming together.
The station has changed over the years, but when I first put it together, it was in a gutted GE Master repeater cabinet. I used an Astron RS-20a power supply, that fed a 400 cca sealed gel cell, and had this elaborate switching relay, that would automatically switch over to straight battery power, if the A/C dropped.
I had a Kantronics 9612 running a true cross-band gate between UHF (at 9600 baud) and VHF (at 1200 baud). The radios were a set of matching Kenwoods, a TM-231a, and a TM-431a, both running into a Diamond duplexer. The TNC was hooked to a US Robotics 9600 baud external modem. It also had a volt meter, and an override switch to simulate an A/C power outage. I also had an SWR meter, and an A/B switch so I could easily hook a laptop up to it. I put this all together at home, and here it is shown below, less the VHF rig. You can see the duplexer and bulkhead connector on the upper right.
I then bought 50’ of Andrews 7/8" Heliax LDF5-50A hard line. I took that, and the Diamond antenna, loaded up the truck, and went to campus for the install. When I got there, I found the antenna would not fit in the elevators (it was over 17’ long), nor could I snake up the stair well. The antenna did come apart, but since the 500 series was prone to leaking, I had sealed up all the connecting joints. Smart, huh?
So I had to make an appointment with the elevator company to hoist it up on top of an elevator car, which we did that week.
It took me another week to install the hard line, put the ends on, erect the mast and antenna, and install the lightning protection. Once that was done, I was ready to test. Here is the mounted antenna…it is the tallest point on the tower.
August of 1997, I fired everything up. Using the voice mic,
I tested the SWR, and was quite happy with the reading of 1.5:1 on 144.390 MHz. I then turned on the TNC, and the digi was online. I
was able to test the modem connection from within the building, and it was
working fine. It took another couple days to get the TNC commands just right,
but it was up and working. Its original call sign was “N8WCT”, and man was it
booming. I got “heard” reports from as far away as
At that time, high speed (9600 baud) UHF packet was just starting to take off. It was neat that just a few of us, could use the UHF side with virtually no QRM, and alleviating some of the VHF traffic. But unfortunately, in the end, high speed UHF packet never took off from there. In fact, today, it’s dead.
Some time in 1999, it seemed the station wasn’t “hearing” very well. Doing testing, I found it was “missing” about 40% of the packet traffic out there, so I decided to visit the site for some testing. When I got there, I spotted a new transmitter and its antenna on the roof. After some investigating, I found it was the hospitals new 150 MHz paging system, and it was causing de-sense and QRM to my station. I then purchased and added the DCI -145-2H, 2MHz, 4-pole band-pass filter, and the station heard even better than before.
Around 2000, the station stopped transmitting all together. A visit found the old VHF Kenwood dead. I replaced that rig with an Alinco DR-140, and decided to remove the UHF rig due to none use.
I should have known better to buy a cheap radio for such a high duty cycle application…it only lasted a little over a year, and died. I replaced it with a Kenwood TM-241a around 2001. I also changed the call sign to the station to reflect the proper SSID for a digi to “N8WCT-4”.
In 2004, I convinced the IT folks to donate a broadband connection to replace the phone line. It was my intention to hook up a PC, and run PC Anywhere for remote access, however, their switch was in the basement, and I had to figure out a way to get connectivity up to the 25th floor. I couldn’t pull in a cat 5 cable, the run was too long. I could have set up some 10baseT repeaters on various floors, but that would have been a pain. In the end, I found some unused fiber running from the basement to the 24th floor. I was able to install a couple fiber transceivers, and make a short cat 6 wire pull up to 25. My connection was now in place, and I had an old homebuilt mini-tower Pentium III running PC Anywhere, but I wasn’t running any APRS software…I was just using Procomm for Windows as a terminal program to monitor things. I also changed the station configuration, to support the new N-n paradigm.
In late 2007 the old Kenwood peacefully died in its sleep. I woke up one morning to find the station not transmitting, and found the rig dead. Man was that one tough rig. I mean, it transmitted probably more than 50% duty cycle, 24/7, for almost 6 years. I replaced her with an Icom IC-V8000, a 75 watt rig.
I also replaced the aged Kantronics 9612, with a new KPC-3+ with firmware version 9.1, to better utilize the digi functions.
In February of 2008 somebody started to use the PC to surf. The PC was just sitting next to the radio box, and I went up a few times to check on it, but never saw anybody using it. I found some secure space up there, so I decided to hide the monitor. After that, I found the machine was being unplugged, or the network unplugged, power cable pulled…just stupid crap, so I decided I needed to secure the PC.
In May of 2008, I redid the cabinet to maximize space. I mounted the filter at the very top, put the radio and TNC right under that, and removed the emergency switching gear (I never used it, and the building has generator back-up anyway). I left the power supply and battery on the lower level, and bought a Dell Optiplex SX 280. This is one of those “large book” sized PC. I was able to fit it inside the radio cabinet, with no keyboard or monitor. I also decided to test UI-View in KISS mode, and see how it would handle the digi on its own, verses the Kantronic firmware.
This is what it looked like…you can see the band-pass filter at the very top.
Here is a rear view.
In June of 2008, I decided that UI-View was doing a good enough job, and decided to keep it. I then installed PM Maps 8.0, so I could enjoy the map views remotely. I also turned on the iGate-out as well, so any traffic hitting my station gets pumped to the internet. I also dumped PC Anywhere for Ultra VNC. The latter if free, and works just as well as PC Anywhere, so I can now connect from any computer. It also uses fewer resources than PC Anywhere. Here’s a screenshot;
In September of 2008 Justin, W1IX noticed the station wasn’t getting out as it should, and contacted me. We began a good repore, and I found Justin to be very knowledgeable on all aspects of APRS. Because of my hectic schedule, I asked Justin if he would act as the station trustee, and he agreed. He now has full access to the station’s control, and I am very happy to have him onboard.
Getting back to the station…a site visit showed a rather high SWR of 4:1. While on the high side, I let the station run until I could schedule a time to trouble shoot the problem.
About a week later, I was able to visit the site. Upon disconnecting the lightning protection, we found water and corrosion inside the connectors. Because we wanted to be thorough, we took down the Diamond…good thing we did…even though it was “after-market sealed”, water still found its way inside. That was one good antenna. Even with the 500 series known leaking problems, it spent almost 12 years up there and at least 3 years prior, in operation at my house.
So it was now off to the candy store. Justin had recommended the GP-9 Comet antenna, but I was still a Diamond fan, but because of the known leaking issues, I took his advice, and got the Comet GP-9. Here is a shot of my friend Todd, finishing up the install.
is a view of downtown
And another of Ohio Stadium along with a glimpse of the sister tower, Morrill.
After getting everything installed and sealed, I fired up the digi, and tested the SWR. At 2:1, while not perfect, it is typical for being at the low end of the band on a pre-tuned antenna. Justin was at home, and saw it come up. Initial reports were good…Justin said he could copy the digi on his HT in his basement. Later, Justin went out on a long mobile trek to check signal strength, and we were both happy to find that the station was booming! We even found areas and stations that have not heard the digi before, finding coverage to places that were deemed “dead” or previously needed a fill. I can only assume the station was having problems for quite some time before Justin noticed…thanks Justin!
Around October 2008, the station was showing some strange behavior. It was delaying repeating some packets…some as long as 30 minutes. Other packets designated to be repeated were completely ignored. After some research, we found than many folks were having the same issue when running UI-View in KISS mode. It seems it tends to only effect “busy” stations, and with the source code destroyed, it makes it that more difficult to troubleshoot. My solution was to run UI-View in the background as a terminal program, and let the TNC firmware run the RF side. This was great, because we could still use the maps, and UI-View took care of network side, and I-Gate. And if the computer would ever fail, the TNC would continue to operate the RF side.
April, 2009. The radio upgrade is complete. Digi is now running a Motorola Spectra at 110 watts. I’ve got all the ins and outs for the TNC on the secondary interface, this allowed me to keep the A4 control head, and keep the mic and speaker intact, so if I ever needed to do voice, I could. The power supply was upgraded to an Astron RS-35M, and an Optima Yellow Top battery. It’s all mounted in a new larger GE Master radio cabinet, and I added a cooling fan because of the bigger power supply and radio. Hopefully the commercial rig will handle the higher duty cycle just fine.
Here’s a front shot, you can see the added fan on the upper right.
Here’s one from the rear.
December, 2009. Changed the callsign to “N8WCT-1” to reflect the newly adopted APRS SSID standards.
That’s where the station is at today, and while APRS started out with many fixed/weather stations, and few mobile stations, just the opposite is true today. Today there are only four other APRS fixed stations left in Columbus right now, and unfortunately, none are weather stations, however, the mobile/tracking side has increased tremendously, and is running at full speed. We are also trying to implement APRS as a valuable tool…the sharing of information and messaging, just to name a couple…not just “vehicle tracking”.
While the station has a network connection, I do not import (I-Gate Internet to RF) any non-APRS stations and/or data. My interests are in true APRS stations, not inserting data directly to the internet…which is not APRS, nor in the spirit of amateur radio.
73, de Chris, N8WCT