Hello,
If you are looking for a way to make your station more effective on range you might want to try some of the carrier current methods.
Hello,
If you are looking for a way to make your station more effective on range you might want to try some of the carrier current methods.
For instance, if your transmitter has a low pass rf filter on the output then you can use the method of placing the rf carrier of your station on the outside shield of the incoming cable tv cable.
Now how long is that cable out there?
At my site I have some graphics of one method you might want to investigate:
scwis says
Very interesting!
Really enjoying your posts, Dan. Imagine my disappointment at finding out my cable TV service is underground! Grrrr, and I just moved from a place where that line went straight up the side of the building and over to a pole – would have been sweet!
Can’t wait foryour next post ๐
Experimental broadcasting for a better tomorrow!
PhilB says
Very interesting!
Me too!
I have never seen this scheme before. Very interesting.!
What would the cable guy think when he sees that big coil? Maybe it could be made to be removable so you can safely call for service?
Unfortunately for this scheme, I switched from Comcast cable to Verizon FIOS TV (“fiber optic direct to your home”). I don’t know anything about the “cable” in this case. It’s just a big black wire about the same size as coax leading from the pole to a big gray box on the outside of the house. It is nice that we have both Comcast and Verizon available. Nothing like a little competition!
Probably fiber optics will replace coax everywhere eventually. Already, Comcast is countering Verizon with ads touting their big fiber optic network. They distribute via fiber, but not to the street and home level yet.
Rich says
Leaky Coax?
Any r-f applied to the shield of a residential cable TV feed would be using a continuous length of conductor, which would quickly exceed the 3-m length allowed for Part 15 AM, if that is any concern.
The conventional definition of leaky coax is coax having periodic openings in the outer conductor, so that r-f fed down the inner conductor is radiated in a controlled way along the length of the coax.
//
Dan Jackson says
See Part 15.221
You have to read Part 15.221 for the definitions there. There is no length limit to the use of a AC power line length or leaky coax. None are specified. Only the amount of mV/m at the specified distance away from the radiator system.
Please read it careful and those who do should post their interpretation of the reading in regards to a limit therein found on the line length.
The coax choke coil size may not be as large as you think. It might not require as much a 100 ohms jX (inductive reactance). In fact low height radiators on medium wave whether short verticals of low height long wires in software designs seem to have feed points mostly under 10 ohms and down to 1 ohm.
Anyways, this should launch something out there in the world of radio when the idea catches on.
Rich says
Part 15.221 Seen
Dan Jackson wrote: You have to read Part 15.221 for the definitions there. There is no length limit to the use of a AC power line length or leaky coax. None are specified. Only the amount of mV/m at the specified distance away from the radiator system.
It is true that no length is specified. However even for a frequency of 540 kHz, the 15 uV/m field strength limit permitted by 15.221 would apply ~88 meters from whatever is radiating it (see 15.221 paste below).
At 1700 kHz it is even worse, when the 15 uV/m limit occurs only 28 meters from the radiator.
This 15 uV/m value is well under the field strength that the outer conductor of a cable drop will produce at those distances when radiating the power available from a typical Part 15 AM transmitter, against a typical r-f ground resistance.
So unfortunately the bottom line here is that a standard Part 15 AM transmitter driving a long cable shield would not be likely to meet any of 15.221, 15.219 or 15.209.
15.221 Operation in the band 525โ
1705 kHz.
(a) Carrier current systems and
transmitters employing a leaky coaxial
cable as the radiating antenna
may operate in the band 525โ1705 kHz
provided the field strength levels of the
radiated emissions do not exceed 15 uV/
m, as measured at a distance of 47,715/
(frequency in kHz) meters (equivalent
to Lambda/2Pi) from the electric power
line or the coaxial cable, respectively.
//
WILCOM LABS says
Shunt fed radiators
This is just another way of “shunt feeding” an antenna. Broadcasters and hams have used it for decades,it is a novel approach to load the outer coax for CATV. You can shunt load a grounded tower,cable,telephone,guy wire or anything that will radiate in the same fashion. It does,unfortunately,violate the part15 rules. It is NOT considered leaky coax or carrier current,this is a free space radiator when shunt fed and is subject to the 3 meter rule and the 15uv/m rule. Its a good way to have an antenna without putting one up,but I’m afraid it wouldnt fly if inspected by the FCC. You dont want “the knock” on Christmas for sure! Merry Christmas to all….
Regards,Lee
http://www.freewebs.com/wilcomlabs/index.htm