geoffstechno (geoffstechno) wrote,

back again

I had not realized that I had not posted anything for almost 2 years, so I'm going to try to get back into things again.

Last week was Rosh Hashannah. In Jewish custom, it is a time of new beginnings, so I think it is an excellent time for me to start my blog over again. 

It's hard to summarize the last 2 years in a post, or even thing of how, so I will start with a problem I had and how it was resolved.

Being a ham radio operator, I have radios and antennas. In between are wires. The wires are the point of this discussion.

When the undersea telegraph cables were laid around the turn of the 20th century, there was a problem with the wires. Each wire had to be bundled together with a return wire. Basically for each each out there had to be an in, or there would be problems with the signals being crossed. To save space and effort coaxial cable was invented. This is a wire within a wire. The center conductor is covered with insulation and then another wire is wrapped around it.

When radar was being developed before WWII (yes, there was a radar set at Perl Harbor), someone figured out that a coaxial cable was the best thing for those signals. Instead of a wire wrapped around the inner wire, a copper braid was used.

Coaxial cable or COAX as it now called (pronounced coh-axe) is used for almost all radio applications and things like video cables,

There is my problem. Ham radios use a specific type of coax and connectors on the ends. TV signals use a different type of coax, and different connectors. Ham radio coax here in Israel is hard to find, the connectors (I thought) next to impossible,

It turns out I was wrong about the connectors, they can be ordered, they are just very expensive. In the US they are called PL-259 plugs and SO-239 sockets. In Japan they are called type M connectors. Here they are called UHF connectors. They used to be called UHF connectors in the US, but that was when UHF frequencies were below the FM broadcast band (just after WWII).

Since 1965, UHF has meant something very different due to the UHF TV channels, which became mandatory in the US on all TV sets.

So I went for around 13 years looking for connectors I could not find, because no one knew what I was talking about.

Meanwhile the coax cable hams use is still hard to find and has to be ordered by the 100 meter roll. There is someone near the airport who sells it in shorter lengths, but they are not anywhere I can get to. 

UHF connectors are expensive (I said that, didn't I), and have to be soldered onto the wires. Soldering UHF connectors is an art. I once was passable at it, but 13 years of not doing it has taken its toll.

So I have been using cables I brought with me from the US. They were outside for a few years when I lived in Philly, and so they were getting pretty old.

TV coax was not very good, and generally you had to order it from a specialty shop to get anything decent. In the last 14 years, the advent of high quality home television, satellite and cable TV has changed that. The standard TV coax you can buy at the mall is far better than the average ham coax that I could get 14 years ago and a lot cheaper.

They are different and can not be used for the same things. If you try to transmit a high power signal, I am licensed for 1000 watts, it will melt and short out, causing all sorts of havoc. Using it for reception, or low power transmitting is not a problem. Modern coax is designed to keep signals in, so that your cable or satellite dish signal does not interfere with your radio or TV. It therefore keeps any interference out, and does not leak transmitted signals into the world, causing interference.

Satellite dishes have equipment at the dish end that needs power, and it goes up the coax. So the coax is designed to carry a decent amount of electricity.

This makes it perfect for ham radio use, or at least my ham radio use. Someone wanting to run microwave links, or use high power would find it is not what they want, but I am perfectly happy with it.

The problem is connectors. TV coax uses a copper center wire, but aluminum as the outer conductor.  It is very difficult to solder to aluminum. A company called LACO sells special compounds to make it easy, but their middle east distributor will not answer any requests from Israel, and the company won't "go around" them.

Well, I have lucked out. Since the demand for good, weatherproof, easy to use connectors has been fueled by the cable TV and satellite industry, a new type of connector has been made. They are called compression connectors, and work by squeezing the front and back of the connector together trapping the coax in it. They have internal water resistant seals, so the connectors can be left out in the rain.

Previously the connectors were screw on, which worked by trying to grasp hold of the cable by screw threads. Most of the time, they did not make a good contact with the braid, and often fell off. The other kind were crimp on, where you stuck the connector on to the end of the coax, and squeezed a ring around it. Squeeze too hard and you deform the coax, making it bad at radio signals, squeeze too softly and it falls off. Squeeze just right, and it still falls off after a few years.

There were good crimp on connectors for TV coax, but they were so expensive, and the tools so hard to get that only the cable TV company installers had them.

So now I can go to the local Home Center (our equivalent of Home Depot) or ACE and buy a roll of TV coax, cut it to length and install compression connectors on it. The connectors and tools are available here and from hundreds of eBay dealers. I've bought them from both, but that's another topic.

Adapters to UHF connectors are hard to find and have to be ordered from outside of Israel. I found a local source of adapters for a different connector, and found compression ones on eBay.

So I was able to run new coax cables to my antennas. They only lasted a few weeks, but that's next time's story.

Geoff.
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