Twelfth Wave Transformer

[kh2]

ok- the title sounds way smarter than I, and just stepped into an unknown area. Scenario is a house wired with RG6 for satellite and would like to "play" with the idea of using that RG6 for an antenna lead. The sat dish would swap out for a UHF/VHF transmitting/receiving antenna. I understand on a simple level the losses inherent in RG6 and by no means a perfect idea. I ran across the Twelfth wave transformer here Twelfth-wave Impedance matching Sections for Coaxial Feed Lines and related sites. It seems straight forward enough and I'm game for the experiment. But I'm not as bright as the subject, my initial questions

I ass-u-me the calculated lengths are physical as the formulas use velocity factors to calculate length.
How are the lengths of coax connected to each other, connectors with extensions or...?
would the length of calculated coax include connectors IE end of connector to end of connector?

Appreciate any initial insight - please keep it simple as possible.

 

[nd5y]

Connectors are part of the transmission line so they affect the electrical length. The wavelength and frequency determine how critical the length is. Connector length probably doesn't make much difference on HF but probably does at VHF and higher. If the formula or calculator doesn't specify the type of connector then you would have to figure it out or build it and measure it yourself.

 

[popnokick]

ok- the title sounds way smarter than I, and just stepped into an unknown area. Scenario is a house wired with RG6 for satellite and would like to "play" with the idea of using that RG6 for an antenna lead. The sat dish would swap out for a UHF/VHF transmitting/receiving antenna. I understand on a simple level the losses inherent in RG6 and by no means a perfect idea. I ran across the Twelfth wave transformer here Twelfth-wave Impedance matching Sections for Coaxial Feed Lines and related sites. It seems straight forward enough and I'm game for the experiment. But I'm not as bright as the subject, my initial questions

I ass-u-me the calculated lengths are physical as the formulas use velocity factors to calculate length.
How are the lengths of coax connected to each other, connectors with extensions or...?
would the length of calculated coax include connectors IE end of connector to end of connector?

Appreciate any initial insight - please keep it simple as possible.

I use the old existing satellite TV 75 ohm coax in my house as a distribution system for the VHF / UHF scanner antenna that is in my attic. The 75 ohm impedance of the cable works fine BUT it is a receive-only system. You may find that trying to use it for transmitting is much more difficult as the lengths and VF of those matching sections will be very critical at VHF / UHF freqs. In addition, if you are going to transmit ensure that you have disconnected all of the splitters / drop amps that may be located in your old satellite / CATV system. For receiving use only, those distribution amps / splitters are very useful.... gives you a scanner antenna port in every room where there a satellite TV outlet is located. But for transmitting you don't want any of that stuff in the line between your antenna and your transmitter... assuming you can get a usable match for transmitting. You certainly won't with multiple drops or a splitter / amp in the line.

 

[kh2]

Thanks for the replies! I will get some connectors and give it a whirl. I'm fortunate enough that the cables are direct to a distribution box so no splitters involved and if it does work...... I can have the antenna in any room.

Thanks again

 

[popnokick]

Well, not quite. If after carefully doing your calculations and cutting on one of the sections of cable… and applying the additional coax “stub” to get a proper 50 ohm match so you can transmit… as soon as you decide to disconnect from the distribution box, you have a whole new section of cable that will need proper measurement and matching. Not an issue for receiving, but if you plan to enable transmitting from any room of the house you’re going to be busy measuring, cutting, connecting, and checking each of those segments for a proper match.

 

[prcguy]

Using 75 ohm coax with a 50 ohm antenna and radio is not that bad, the match might be a little off but it should work fine without any external matching.

 

[kh2]

Popnokick - I appreciate the insight I should have been more clear I could choose which room to work from. the "shack" would be in one location.

And thanks for the input - prcguy