Tuesday, February 14, 2012


DOSI (Department Of Stupid Ideas)

As I mentioned before, sometimes I do think a little and when that happens strange ideas do pop up!

Here's one:

This idea came to life when in one of my work travels. I was at the hotel room thinking that would be nice to operate an ham equipment at HF, problem is that I end up always on northern parts of the hemisphere well know for a not warm climate (for not saying bloody cold for a Mediterranean climate inhabitant!), so opening the window was not an option to place an antenna or I would became an ice cube....the other option was to place the cable and closing the window...but I think the normal 50 Ohm round cable would not like the idea...

So two ideas pop up:

1 - A windows pass-thru cable made of thin wire

I did some quick tests and the design works till 10Mhz (using 50 Ohm system), of course I believe a smaller distance between the wires could extend to higher frequencies, this was just a quick test, the distance between wires I made has an impedance more near 300 Ohm than 50 Ohm.
There are some commercial window pass-truth used for satellite installations (75 Ohm) that could be used in 50 Ohm system but I didn't tested any of those, maybe someone can test them, this was just an idea not for production, at least not right now.

2 - A coupling link working from the inside (antenna tuner) to the outside (antenna) like on the Z match tuner.

I made a small coupling coil about 10cm diameter connected to the antenna analyzer and another similar coil connected to a 50 Ohm load, then placed them at a small distance similar to the glass depth (about 5mm). Measuring up I end up to the conclusion that the ideal distance is the coupling link inside the transmitting link (like on the Z match, be it open air or with a toroid).
Unfortunately I didn't take photos of the rest fixture. This system might work on lower performance but further testing is necessary.

There's still another method I came up....the coupling cap method but didn't test it, a small aluminum plate inside the window connecting the transceiver cable and another one outside the glass connecting the antenna, being the ground wire radials in the inside.

Conclusion: Further and more precise tests must be done. I just left here the ideas, it might help someone. I haven't traveled that much in past times that justify making something.

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