Good Digital antenna cheap!

Step 3 Attach twin lead

Strip and attach a piece of 300 ohm twin lead (TV antenna wire) with two sheet metal screws. Attach a 300 to 75 ohm signal or impedance matching transformer to the other end of the twin lead.

Comments

[rowerwet]

what do you mean by 300 ohm wire, that the resistance of the wire is 300 ohms? or is it a wire rating of some kind?

[Phil B]

Cables for connecting an antenna or other signal device (DVD player, etc.) to a television have an impedance given in ohms.  Impedance is a form of resistance to the flow of current and is different from simple resistance in that it involves circuits in which coils of wire (inductances) or capacitors interact with currents at various frequencies.  As the frequency of the current changes in these circuits, so does the resistance to its flow.  A coil of wire may present only a couple of ohms of resistance to a straight DC current, but apply a current at radio frequency and that coil presents several hundred ohms of resistance to the high-frequency current.  That is why small coils of wire in a radio circuit are called a choke.  300 ohm twin lead is flat TV signal cable that presents 300 ohms of resistance at television signal frequencies.  See this article.  Coaxial cables more frequently used now for digital signals have an impedance of 75 ohms.  A small transformer can convert the signal from 300 ohms to 75 ohms.

[static]

300 oms means that twin lead has a characteristic impedance of 300 ohms. Most UHF TV antennas use a folded dipole as the driven element, a folded dipole has a characteristic impedance of 300 ohms that's why twin lead has been used over the years, so there's no impedance mismatched. LOL just dawned on me you are feeding a plain dipole that has a characteristic impedance of 75 ohms with the twin lead. No matter rabbit ears use twin lead, and all works sometimes. that why the term is "characteristic impedance.

[rowerwet]

thanks, I never knew that and I wire stuff at work all the time, mostly DC though so low ohms readings.

[Phil B]

I do not work with these things, but have read bits and pieces about impedance, also known as reactance.  In a radio tuning circuit there is an inductance (coil of wire) and a capacitor.  One of those is variable by means of a tuning knob.  The resistance provided by the inductance reduces or blocks signals.  The same is true for the reactance or resistance provided by the capacitor.  But, at the selected or desired frequency of the station you want to hear, the reactance from the capacitor has the effect of countering the reactance or inductance from the coil of wire.  The result is the frequency you want is allowed to pass relatively freely. 

I am glad to have been of help.

[mackenpoy25]

g

[Phil B]

I do not text, so I am not quite sure what "g" means to you.  But, thanks.