New project on www.sm0vpo.com - RF Window Transition Cable

Hi Andrew,
what a nice idea! Copper strips can be bought in various widths and lengths e.g. here. If two strips of adhesive plastic tape (cca 40 mm wide) were used and two copper strips were inserted between them side by side, many meters long and very thin balanced lines (twinlead) could be made. The characteristic impedance would be set by the width of both copper strips and the distance between them.

VBR from Ivan

sm0vpo wrote:Hi all,
I have added a new project to the homepages.

http://sm0vpo.com/antennas/cable_transition.htm

I have a lot of things on the desktop at the moment, but having the office window open 24/7 during the Swedish winter forced me to prioritise this little gem.

My window was open because I wanted to get an RF cable fed into the house, and I did not want to bore holes in the nice, new window frame. The are commercial cable transition cables available for this purpose, but they are designed for TV receive only. I didn't want to wait weeks for delivery, only to find a pyrotechnic display when I try to transmit.

Mine works for all frequencies up to 30MHz. I have tested it briefly at 145MHz and it did work, but I didn't try more than 5 Watts on TX. There is no reason why it cannot be used as a leadin for a solar panel, providing there is some current limiting from the battery.

My own cable transition is dead-easy to make. All the materials you may be able to "borrow" from work. There are only two materials - Plastic lamination sheet (with access to a laminator) and some copper tape.

Hi Harry, nice job, just an idea; since the two laminated sheets are actually a "balanced line", even if a very short one, did you consider the idea of adding a "guanella" choke between the inner ends of the sheets and the coax cable to both eliminate CMC and help cutting off some noise ?

Also, and since I'm at it, the "sheets" may be useful to use a balanced line (in place of coax) to feed your antenna, in such a case you'll have the "ladder" (ok, 300 Ohm flat twin line) running from the outside of the window all the way to the antenna and a 1:1 choke/balun (guanella) to the inside of the "sheets", connecting with a (short) run of coax going to the rig (or the ATU), such a setup aside from the "complexity" of setting up the balanced line (which can't run on ground or near "obstacles") would allow you to minimize losses and, at the same time, put up a "doublet" antenna !

What else... oh yes, I'd place a pair of electrical junction boxes both, inside and outside the window to protect the junctions and at the same time help with mechanical strength

Hi,
I had the same problem - I needed to pass a coax through a closed window without drilling. My window is wider than the Harry's one and 20 cm seems to be too short. Moreover, the solution by Harry is in fact a balanced twinlead, so it includes two transitions between an unbalanced (coaxial) and balanced line. I tried another approach - a microstrip unbalanced line in fact. And as an advantage, I did not need a laminator.

What I used:
* adhesive packing tape 38 mm wide, its type is not critical, it must have zero conductance in any case (no "silver" tape with aluminum, please);
* enameled copper wire (magnet wire) 0,20mm dia, its diameter affects both the impedance and thickness of the resulting cable;
* PTFE (teflon) sealing tape for plumbing 16mm wide, the material and the thickness of the tape affect the impedance even more;
* a strip of metal foil 38mm wide, copper is the best one. I did not have copper one at hand, so I used brass one, which may cause slightly more losses. Kitchen aluminum foil should do, if you can solder it, hihi.

What I did:
1 - I stretched the required length of the adhesive tape on my table, the glue upside;
2 - I put a piece of magnet wire along the center line of the tape, exceeding cca 2cm on each end;
3 - I covered the wire with teflon tape and pressed to the glue;
4 - I covered the "sandwich" with brass foil so that it matches with the adhesive tape. I pressed firmly - no air bubbles shall stay inside and no moisture shall find its way into the cable;
5 - if you want, you can cover the metal foil with another piece of adhesive tape (glue downside now), but I omited this step on my sample; the metal foil is grounded in most applications;
6 - I released the microstrip cable from the table and soldered coax on both ends, the braid to the foil, the center conductor to the wire;
7 - I recommend to wrap the connections with adhesive tape thoroughly to weatherproof them and make them mechanically stronger. If water soaks into the coax braid, it may get very far and destroy the whole length!

The results:
* the thickness - my caliper shows 0,28mm;
* characteristic impedance, maximum power and losses on receive - to be further tested.

VBR from Ivan OK1SIP

Ivan wrote:Hi Harry,

your text is O.K. now. Well done !! BTW, the draft you have sent to me was O.K., too.

I am going to try a different solution of this topic. I will post some results here.

VBR from Ivan

Yes, the text was ok because I opened the file directly from my memory stick, not downloaded it from a web server. It is the web server that adds stuff to the special characters (° ± Ω etc).

I will be very interested in your solution.

BR Harry - sm0vpo

Hi Harry,

your text is O.K. now. Well done !! BTW, the draft you have sent to me was O.K., too.

I am going to try a different solution of this topic. I will post some results here.

VBR from Ivan

Hi Ivan,
I found that the problem is my HTML editor (notepad.exe), which saves raw ASCII text by default, and not "UTF-8 with BOM".

Now I think you will find it is corrected. Thank you very much for pointing that out to me. I really appreciate it.

BR Harry - sm0vpo

sm0vpo wrote:... commercial cable transition cables available for this purpose, but they are designed for TV receive only. I didn't want to wait weeks for delivery, only to find a pyrotechnic display when I try to transmit.

Hi all,
types designed for transmitting exist too, but they are quite expensive. See e.g.
Comet up to 100W PEP on HF
Diamond up to 150W PEP on HF, 50W CW
from China power unknown, cheaper, maybe RX only?

VBR from Ivan OK1SIP

Hi Harry,
please check the font you have used in the article. Strange characters appear in my browser (the latest version of Firefox) through the whole text. Most of them are A with a small roof (French accent cirquonflexe) above. A sample is here:
VBR from Ivan

Hi all,
I have added a new project to the homepages.

http://sm0vpo.com/antennas/cable_transition.htm

I have a lot of things on the desktop at the moment, but having the office window open 24/7 during the Swedish winter forced me to prioritise this little gem.

My window was open because I wanted to get an RF cable fed into the house, and I did not want to bore holes in the nice, new window frame. The are commercial cable transition cables available for this purpose, but they are designed for TV receive only. I didn't want to wait weeks for delivery, only to find a pyrotechnic display when I try to transmit.

Mine works for all frequencies up to 30MHz. I have tested it briefly at 145MHz and it did work, but I didn't try more than 5 Watts on TX. There is no reason why it cannot be used as a leadin for a solar panel, providing there is some current limiting from the battery.

My own cable transition is dead-easy to make. All the materials you may be able to "borrow" from work. There are only two materials - Plastic lamination sheet (with access to a laminator) and some copper tape.

Very best regards from Harry - sm0vpo

I have updated the homepages at:

http://www.sm0vpo.com____[url=http://www.sm0vpo.com /]      [/url] (main site) [port 443] and the WWW is optional. It works without (http://sm0vpo.com)
http://www.sm0vpo.com:80          (alternative, hosted on a Raspberry-PI)
http://www.sm0vpo.com:81          (test/trial server, hosted on a Raspberry-PI) for me to play with
http://sm0vpo.altervista.org/        (mirror site, no downloads or PDF datasheet library)