The 70cm Yagi – $18 (minus coax/connector)
A local contact that I made on the ISS, KF4GTA, suggested that I try out working some FM “birds” when he checked into the Colquitt County Ham Radio Society’s friendly net this week. He mentioned SO-50 and AO-27, and so far I’ve worked the SO-50. At first I didn’t think that I had the right equipment, but then I remembered that my FT-60 was a dual band transceiver that did both 2m and 70cm. Shortly after that realization I was working towards working the birds.
First, I downloaded HamSatDroid on my Samsung Tab and my Motorola Razr. I then added my position and updated the Keps. I noticed there was an AO-50 pass around 10:30pm EST so I started preparing.
Second, I grabbed my FT-60 and my Arrow 146-4 (which is not optimal for 70cm, but it would work in a pinch). I connected that to my radio and then I added the satellite frequencies to it.
Third, I then had to re-enter the frequencies because I knew I needed to adjust for Doppler. I’ve never really had much interaction with Mr. Doppler except for the occasional ambulance, so I was pleased to see how well the Doppler effect worked on a 70cm signal. I have the downlink ranging from 436.805 to 736.785.
I made my first contact using the Arrow 2m antenna, but I instantly forgot the call sign. I also had a very weak audio from the downlink so that is when I started thinking about building a small directional antenna. The parts that I gathered were: Continue reading
For Christmas my wife bought me a “backpacker” Yagi antenna made by Arrow. It is the 146-4BP, and it consists of a 3 piece boom and four elements. I wanted to use this as a portable antenna, but I missed out on one thing. I didn’t tell her to buy the mount. The mount is only $9, and is very well designed, but unfortunately after shipping would cost much closer to $20, so I decided that I would forgo that.
What I decided to do was to drop back and return to my PVC days. Instead of a potato cannon, I would make something much safer. I went to the hardware store and purchased a handful of items.
- stick of 2″ sch40 PVC pipe
- 5 – 90 degree 2″ elbows
- 3 – 2″ cleanout tees
- a pack of 3/4″ conduit clamps (Need 2)
- I already had a few washers and screws
Cut the PVC pipe to the lengths in the first picture. These should be two 15″ lengths, four 2.5″ lengths, and two 5″ lengths. The great thing is that you are not limited to these measurements. If you want a larger base, modify the cuts. Just keep in mind that the center piece relies on the two long pvc cuts. They need to be snug so that they don’t slip out.
For the antenna clamp, I used the conduit clamps to hold the antenna into place. This is most effective as a vertically polarized antenna, but may work alright as a horizontal. I cut a piece of 2″ PVC for this, and I didn’t measure. I just made sure that the clamps were in line. The second photo shows how to make this work. I had to bend the clamps down to the PVC to get a good grip. Using some rubber sheet would have made this connection a little more snug. I also cut a notch out the the elbow so that the boom didn’t bind against it. You can barely see this notch in the photo.
Finally, I used the remaining length of 2″ pipe as the mast.
This whole project cost less than $20 dollars. The elbows were 88 cents each, the tees were $1.50 each, the PVC pipe was about $7, and the clamps were about $1.50 a pack. The screws were free.
I was telling my cousin, Ken, about my antenna, and I mentioned that I lost my compass that I was using to direct it and I was estimating where certain repeaters were located. He gave me a good idea. Why not print a strip of paper with the degree marker to wrap around the PVC pipe?
Great idea. I’ll put a tick mark on my mast (the part that doesn’t move) and then glue the strip to the rotating portion of the mast. Then I can align it up one time using a compass, and then I’ll have a quick and easy way to align the antenna after that. He discussed soaking the paper in a super glue mixture, but I think I will just use some clear tape to secure it.
The first step is to find the circumference around the pipe. Pi*diameter. For my case, the circumference is 5.215″. In Inkscape I chose to use pixels as the measurement. The resolution is 90px per inch. The length of my compass will be 469.35 pixels, and each 1.30376 pixels is one degree. Using guides in Inkscape, I marked out ten degrees with vector lines. Then I copied those ten (including the zero mark) and pasted them. After aligning the zero and the ten mark, I copied the twenty degrees and pasted them. After aligning I copied the forty and pasted. Now I have 80 degrees pasted. Then 160. Then 320. Then I pasted 160 again and deleted all those that came after 360.
Now I just have to print it and affix it to the mast.
Azimuth map - http://ns6t.net/azimuth/azimuth.html
The other day my uncle came up with a neat little design for a light pole that he moves around the shop. It uses a 1.25″ pvc compression coupling. I used one of the threaded ends to connect it to a 2″ cleanout fitting. The threads fit close enough that it screwed together. This is so that I can pack the antenna and mast up and move it. It actually carries around quite nice.
Pictures are a must, and I will post them soon. I just wanted to blog that I was able to hit the KE4URL repeater with 2.5 watts (which I estimate at 40+ miles). I also hit WG4JOE’s repeater which is located in Parrot, Ga.
I was able to get the side tone through KE4URL, but at 10pm, nobody was talking. I marked the spot with a marker on my mast, then I estimated that the other repeater was at about 10 degrees based on a contact that I made while mobile on that repeater.
WG4JOE answered, but he informed me that my transmission was hardly intelligible. I climbed the ladder and turned my antenna about 10 degrees towards the west and gave my call sign again. He almost caught most of it, but he heard Moultrie and suggested that we switch to my local repeater to talk.
While on the local repeater I could use a half watt with no worries without directing my Yagi. I informed WG4JOE that I was using an HT with a low battery and that my antenna was pointed at 10 degrees North then 0 degrees North, estimated. He said that I would probably get a better copy if I turned the repeater to about 310 degrees or so. After looking everything up, it appears that he was about spot on. 310-320 degrees. I will try that some day this week and see what the results are.
Another thing to note is that feed lines make a big difference. I had been using a cable that was coupled together, and the losses are pretty insane through the coupling. A single piece is the way to go.
I am very happy with my scrapyard Yagi. Even though the Yagi wasn’t pointed directly at WG4JOE, that was still a 100+Km contact.