Feb
16
2012
It’s going to take a while to get to the computer related material in this article. Please be patient.
Ever since I was a little kid I’ve been curious about the world around me. I was the type of kid who wanted to see what was on the next block or figure out how dolls were made (yes I took them apart and put them back together again). The only time I got into trouble for it was when a big kid thought he was doing the neighbourhood parents a favour and told us little kids not to go near the river because there was a big monster there. We wouldn’t have gone there anyhow but we really wanted to see that monster. We were so disappointed we told our parents. I didn’t see why they were so upset. We made sure not to go near the river. We stayed a whole six inches away from the water. 
Later I wanted to figure out as much as I could about radio and TV. I used to lay awake for a couple of hours per night listening to short wave and AM just to see how far away the stations I could pick up were. As I recall, the name of the hobby was called DXing. I was able to get stations from South Africa and Moscow on short wave and as far south as the American gulf coast on AM. Now all I can get on short wave is Radio Cuba and American religious stations. TV was similar. When I wanted to see what was available over the air we only had three Canadian stations and one American station. With the switch to digital (many years later) I found we had six Canadian stations and (depending on location) one American station. Actually we have cable in the house and I am satisfied with it. It’s just that I’m still curious about what I can get locally.
I mentioned this to a friend at a local computer club and he suggested I connect my cheap LCD TV to an external antenna. I had previously connected it to our old VHF antenna and was pulling in five of the six Canadian channels. The American channel was a lost cause. He pointed me to the “coat hanger” antenna plans at Make magazine (it’s a DIY magazine like popular mechanics used to be). After reading the description I found it to be a UHF antenna. This was fine for me since four of the local stations were now on UHF (including the one I couldn’t get earlier). The other two Canadian stations and the American station were on VHF-High. I built the antenna and had some interesting observations. In the basement I was able to get two stations. That makes sense because UHF frequencies are basically line of sight. On the ground floor of a house covered in stucco (which filters out some signals) I was able to get all four UHF stations (including the one I couldn’t get before) and one of the VHF stations. The quality of the signal also improved since there were less “drop outs”. After a bit of research I found line of sight improves as the height of the antenna increases.
Not being satisfied I did a bit more research. First off, TVfool.com (a list of TV signals theoretically available in a given area) showed there were additional stations just beyond the horizon. On a good day before the digital conversion we used to be able to pick up two of them when the signals bounced off the troposphere. Apparently there are another three or four more in the area. Then there was video of one guy who lives slightly North of me being able to pick up Minnesota stations. This was a shock because North Dakota is directly to our South and much closer. It was about that time when I discovered plans for the Grey-Hoverman antenna (released under the GPL3). Apparently this antenna is so sensitive it puts the coat hanger antenna to shame.
While I was out shopping for material to build the new antenna I was talking with a sales person and a TV engineer I met at an auto supply place. They both decided to give it a try themselves earlier than I had. One of them was using a TV tuner card on their PC with the four inch antenna that came included in the box. The other guy had an expensive TV with a cheap commercial antenna (he was opposed to cable and satellite TV on principal). Their experiences were strange. Apparently neither were satisfied with expensive commercial antennas and found the cheap ones were just as good if not better for their needs. Both were able to pick up all the stations in town as well as the American channel. I told them what I was looking to do and I was looking to spend $10.00. They said for that price it was worth giving it a try.
At the moment the build for the Grey-Hoverman antenna is stalled due to a cold.
Here is the computer related part. Another computer club was looking for a presentation last month. I figured since I had the coat hanger antenna we could look at a TV tuner card. A member of the club has a friend who works at a local computer store and he asked me if he could help. I suggested he see if he could borrow a cheap $50.00 digital tuner card. The store loaned us the top of the line $250.00 card for the meeting (Thank you MyMacDealer for the free loan). On the day of the meeting I realised the building was of a cinder block and rebar type construction. It also had lots of steel heating ducts and such. Essentially this meant it was worse than my house for getting signals. Plus we were also meeting in a room smack dab in the center of the basement. The package didn’t come with the four inch antenna I anticipated. It didn’t come with any antenna at all. I had my doubts it would work. Without an antenna there was no signal at all. With the coat hanger antenna it brought in one strong and one weak signal. Much better than expected. I showed the plans for the coat hanger antenna to an engineer as well as a city technologist. They thought the design was very ingenious. A couple twists here and there introduced some noise cancellation features. According to what they said the coat hanger antenna performed much better than expected.
Once I build and test the Grey-Hoverman antenna I’ll approach the other group and see if they want to do a live demonstration of Myth-TV. This way they can test the two antennas side by side. They will be using a different tuner card. The one for the Mac had a single tuner and connected to the USB port. The one these guys use has two tuners and is an internal PC card. The cost of this particular card is about $150.00. Boiled down to the nitty gritty… The TV tuner cards work. If it doesn’t then return it and try a different model.
Some DIY stuff… The construction method I used with the coat hanger antenna was pretty shoddy. Further reading suggests it is really hard to go wrong with this one. Just make sure the wires are not touching when the connecting elements cross (insulated wire is a good choice here). The coat hangers should be scuffed so as to remove any paint and rust so they can come in contact with the connecting elements.
For the Grey-Hovermann antenna it is best to build a jig for bending the wires to the correct angle and cutting them to the correct length.
If anyone is looking for increased sensitivity and distance, connecting two identical antennas together will work. However anything more than a dual bay (two antennas) results in diminishing returns and isn’t worth the effort.
It is possible to angle both antennas in a dual bay differently. However if they are at a 90 degree angle the signals cancel out.
Reflectors can increase the sensitivity up to 30% but turn the antenna into a directional antenna.
Using wood as a mounting material means the antenna is designed for indoor purposes only. Outdoor antennas are typically mounted to PVC or insulated metal.
Outdoor antennas need to be grounded.
For the most part for a basic antenna, scrap material can be used for minimal cost. Using better quality materials and better construction methods will improve the output somewhat.
As a radio tech friend once told me. “All you need to get a signal is a long enough piece of wire. Anything else is just getting fancy.”
By BlankMike •
Design, Do it yourself, Documentation, Hardware •
• Tags: hardware, TV, video
