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Part 15 on Long Wave?
- Thread starter audioguy
- Start date
Why?
I guess the answer is "why not?" The band is available, so why not take advantage of it? We are permitted to use up to 1 watt which is 10x the power in the MW band, although the antenna length is physically a much smaller fraction of a wavelength so efficiency is not great. But I am curious to know if anyone has tried it and what kind of distances they were able to cover. I have several European LW portable radios that could be used to pick up the signal.
If you're referring to "lowfer" operation I hadn't played with that since my pre-teens and teen years. It was fun to experiment with but with only two people I knew at the time having radios that tuned that low it wasn't much fun.
What kind of antenna would you need to achieve the proper resonance (if 'resonance' is the right word) ?
In the 60's we had the usual Lafayette 150 mW unit, and broadcast music and other teenaged mischief. The electronics wizard in our midst placed three tuning coils in between the transmitter and the supposed 10-foot allowable antenna.
Our antenna was a little longer than the legal ten feet. But only by about 260 feet, strung through alley backyards.
The resultant signal was about 20 feet wide and 1000 feet long.
That was with with everything 'tuned'.
Still, just on a non-tech guess, I'd say that one full watt that low on the dial (and considering the ground conductivity in the area) could carry pretty far.
If the antenna were somehow attuned to it all.
What kind of wave length is there to, say, 300 kHz ? 50,000 feet, lol ? Would one watt even make it all the way to the far end of the antenna wire?
In the 60's we had the usual Lafayette 150 mW unit, and broadcast music and other teenaged mischief. The electronics wizard in our midst placed three tuning coils in between the transmitter and the supposed 10-foot allowable antenna.
Our antenna was a little longer than the legal ten feet. But only by about 260 feet, strung through alley backyards.
The resultant signal was about 20 feet wide and 1000 feet long.
That was with with everything 'tuned'.
Still, just on a non-tech guess, I'd say that one full watt that low on the dial (and considering the ground conductivity in the area) could carry pretty far.
If the antenna were somehow attuned to it all.
What kind of wave length is there to, say, 300 kHz ? 50,000 feet, lol ? Would one watt even make it all the way to the far end of the antenna wire?
I wouldn't be discouraged to try experimenting even though it may seem futile.
Just take any modern day radio that can tune down there and you will be surprised to hear how many beacons and lowfers are on there using very little power.
1 watt into a 49' (15 meter) pole with a top hat or top loading can get out surprisingly well on longwave and if the receiving station also has a similar setup you can communicate for tens to hundreds of miles using CW or slow mode data.
Now for AM you aren't going to achieve that sort of distance but it would still be fun to try.
Personally I would recommend SSB since it's not that much harder to build a tiny DSB or lower/upper sideband transmitter.
1 watt should be extremely easy to work with and design a transmitter around given that even most high power audio transistors will work as RF parts up into the high longwave, or lower mediumwave bands with lots of gain to spare.
The reality is that the field strength on longwave won't be much different than mediumwave part 15 when going by the rules. So expect about 1/4 mile at best for AM on LW. What you do have working for you is that the band is free of other competing stations unlike MW and this could possibly be beneficial to night skip and winter season conditions as many LW radio listeners know.
Best antennas to use for longwave would be the T type antenna or the inverted L. Maybe even some type of horizontal or vertical loop.
I think for such low frequencies I would go for the T, or usual pole with top sky radials (top-hat) to bring up current near to the top.
I would imagine the funnest part about longwave would be experimenting with antennas since that is either the strongest or weakest component of the whole setup when efficiencies are that low.
One last thing.. I question if AM would even work well given the antenna constraints since the bandwidth of such a short antenna and little to no earthing would be minimal. Wonder if this would squash any fidelity had by AM?
There really needs to be a company out there that starts selling kits for LW two way communications. Not sure why Ramsey Electronics or the like hasn't caught on yet as I know there is a market out there for experimenters.
Just take any modern day radio that can tune down there and you will be surprised to hear how many beacons and lowfers are on there using very little power.
1 watt into a 49' (15 meter) pole with a top hat or top loading can get out surprisingly well on longwave and if the receiving station also has a similar setup you can communicate for tens to hundreds of miles using CW or slow mode data.
Now for AM you aren't going to achieve that sort of distance but it would still be fun to try.
Personally I would recommend SSB since it's not that much harder to build a tiny DSB or lower/upper sideband transmitter.
1 watt should be extremely easy to work with and design a transmitter around given that even most high power audio transistors will work as RF parts up into the high longwave, or lower mediumwave bands with lots of gain to spare.
The reality is that the field strength on longwave won't be much different than mediumwave part 15 when going by the rules. So expect about 1/4 mile at best for AM on LW. What you do have working for you is that the band is free of other competing stations unlike MW and this could possibly be beneficial to night skip and winter season conditions as many LW radio listeners know.
Best antennas to use for longwave would be the T type antenna or the inverted L. Maybe even some type of horizontal or vertical loop.
I think for such low frequencies I would go for the T, or usual pole with top sky radials (top-hat) to bring up current near to the top.
I would imagine the funnest part about longwave would be experimenting with antennas since that is either the strongest or weakest component of the whole setup when efficiencies are that low.
One last thing.. I question if AM would even work well given the antenna constraints since the bandwidth of such a short antenna and little to no earthing would be minimal. Wonder if this would squash any fidelity had by AM?
There really needs to be a company out there that starts selling kits for LW two way communications. Not sure why Ramsey Electronics or the like hasn't caught on yet as I know there is a market out there for experimenters.
I have some ideas.....1 whole watt, huh?
I've been meaning to smell solder soon. "1 mile" wavelength, roger dat.
Does the FCC count a mica cap as the end of the "wire"? Just asking.....
I haven't got time to try this for quite a while, I suppose. Darnitallinthecrisisofthemomentresponsibilities.
I've been meaning to smell solder soon. "1 mile" wavelength, roger dat.
Does the FCC count a mica cap as the end of the "wire"? Just asking.....
I haven't got time to try this for quite a while, I suppose. Darnitallinthecrisisofthemomentresponsibilities.
audioguy said:
Below is a link to a spreadsheet analysis of an unlicensed system on 175 kHz operating under FCC §15.217.
The DC input power allowed at the final r-f amplifier of the transmitter in this low frequency band is 10 times that allowed in the AM broadcast band under §15.219. Even though the radiating length of the antenna system permitted in this band is 15 meters, it has only about 1/3 of the radiation resistance of a 3-m radiator at ~1600 kHz. Also the loading coil needed to resonate the 15-m antenna has higher loss at this low frequency, and probably the resistive loss in the r-f ground connection is greater, also.
So the net result is that the radiated power from the Pt 15 low frequency system is less than the typical value from a Pt 15 MW system, and the usable coverage area for a 175 kHz system would be smaller. Radio noise levels also are higher at these low frequencies.
The loaded Q for this low-frequency system is not very high, but the 3 dB r-f bandwidth of the antenna system in this example is only 2.7 kHz. The audio bandwidth at the output of an AM receiver would be 1/2 that, so this system would be far from "hi-fi" to an average listener.
http://s20.postimg.org/93o4qd2p9/Low_Fer_Pt_15_System.jpg
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