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Leaky Coax Radiator

Page history last edited by PBworks 16 years, 4 months ago

Carrier Current Leaky Coax Radiator

There are various leaky coaxial methods used, however there is an interesting method that will be detailed here. And it is not for use with a Part 15 transmitter that lacks a minimum of a five element low pass rf filter at output. You know, a double Pi network filter design? (You really should always think in terms of this filter being in all Part 15 transmitter schemes.)

This involves the use of existing coaxial cable systems, such as that for use with cable tv. The idea of this method is to place a section of coaxial cable in the cable tv cable. That is wound up into a choke around a PVC pipe form. Much like a coaxial cable type of balun is wound. And the coaxial choke's outer shield, is used for a system matching and tuning coil. This in effect, will not effect the incoming tv signal within the cable. And if the transmitter is well filtered, it will not introduce harmonics into the cable system; and all will be fine. Since this method uses the coaxial cable's outer shield as the intentional radiator and matching coil. Yet, if for some reason, you do this and nothing is fine about it. With regards to the way that particular cable tv coax line is set up. Then do not use this method.

The idea of the choke, is to have no more than 10 to 100 ohms of XL or inductive reactance at your operating frequency across the choke. The cable will be a low height radiator, of the end fed long wire type. Stretched out from telephone pole to pole. And thus will have a low radiation resistance. If the tuning resistance is high across the choke, it will be due to ground resistance.

The choke acts like a tuning coil with reference to the applied Part 15 level rf signal. And the carrier current tuner used to tune the arrangement adds capacitance across this coil to tune it. The outer protective sheath of the coax cable around the PVC form is removed at points to add wires soldered around the cable's outer shield. These connection points act as coil taps. And two rotary type switches are used to short certain sections of the coil out. At the bottom to change the coil length. And another switch is used to adjust the tap point of the feed point. There are from 1 to 3 turns left on top at all times in the scheme, to act as attenuation or harmonic suppression turns. For impeding any harmonic frequency in the cable tv range the Part 15 transmitter may pass. Though the transmitter for this use must have a low pass filter to begin with. And so. If you have no filter then do not do this. Get a filter first.

The choke is located just above the grounding plate of the cable tv cable on the incoming service point. At the watt hour meter service pole or on the outside of the building if that is where the location of the cable tv coax ground plate is.

Remember, the carrier current tuner will add capacitance across the choke and make it look like a parallel tuned circuit.

The interesting thing about this method is that the cable can carry your signal's electrical current, a long ways down the line in your area. And it does not have to exceed the 15uV specification at around 30 meters either. Expect losses. But expect the line to aid the carrying of the electrical current over the local area. And be heard in local places you would not other wise be heard.