Home Amateur (Ham) Radio VHF Experiments In 2 Meter Simplex
Experiments In 2 Meter Simplex PDF Print E-mail
Written by Tim Wray, KB9SNL   
Monday, 29 June 2015 13:48

I have been unusually interested in VHF/UHF simplex as of late. Here in southern Indiana, 2 meters is dominated by repeaters, as in many areas. I find repeater operation uninteresting for the most part, at best, a utility when one just wants to chat or whatnot.


After spending some time with my friend, Scott, KD9CON, at a field day location recently, we picked out a 2 meter simplex frequency of 146.505 MHz and chatted on our mobile radios as we left. I had forgotten how much I enjoyed FM simplex...it brings back the line of sight challenge to local amateur radio. It's just more fun to make such contacts, scheduled or otherwise.


Today, at lunch, we scheduled a QSO, as we work far closer together than we live. We live approximately 30 miles apart, but work only about 10 miles apart. We decided to give the simplex a harder test and communicate at a longer distance from our mobile rigs.


All distance and height measurements are via Google Earth.

Scott, KD9CON, was operating a Radioshack HTX-212 rig at 45 watts transmit power from 737 feet above sea level. He was using a 1/4 wave 2 meter antenna he built from an old citizen's band antenna (magnet mount base) and a cut to length section of an old car radio antenna.

I (KB9SNL) was operating an Icom IC-208H at 55 watts transmit power at 943 feet above sea level. I also was using a 1/4 wave 2 meter antenna, a no-name I purchased at a local ham fest.

Initially, I attempted to contact him from the parking lot of my work place. This was unsuccessful. I had identified a much higher elevation via Google Earth that was nearby, at the Northwest YMCA in Bloomington, IN. I drove up there and gave it a shot. Now, we could make contact, although he had me between s3 and s5 on his meter, and he did not register on mine, although he was readable...not quite full quieting, but we could converse just fine.

Shortly thereafter, a small rain storm moved in over KD9CON, and he became weak, and my readability fell for him as well. I looked to my left and noted a steel light pole, and I decided to give something a try. As my magnet mount antenna was on my trunk deck (it interferes with my moon roof when on the roof), I tried to align the antenna roughly to the light post in KD9CON's North west bearing from my location. I transmitted again, and he noted a marked improvement...s7 to s9! I began to receive him with a solid, non-fluctuating s3.

Meter view video clip of KB9SNL transmission received by KD9CON near Spencer, IN: kd9con_qso1.mp4


Meter view video clip of KD9CON transmission received by KB9SNL near Bloomington, IN: kb9snl_qso1.mp4


Upon a little further study later, I determined that my height was much higher than KD9CON's height, which led to my signal being less impeded going to him, vs. his being somewhat attenuated by terrain (a wild guess on my part, but it makes some sense.) There was a considerably large difference in land height between us (216 feet), with me (KB9SNL) on the higher end. If you look at the elevation profile from Google Earth below, you will not that I was high enough to overcome hills between us, while KD9CON's signal had the challenge of reaching me, so to speak.


Overall, line of sight was good, considering how hilly southern Indiana is. We were 9.49 miles apart.

QSO detail
(Click image to enlarge)

We plan to schedule more QSOs and experiment more in the future, including experiments with SSTV.