2 Good Part 15 Bands For Broadcasting

HF Part 15 stations occupy a narrow slice of the 22 meter shortwave band in accordance with the provisions of 15.225, which specifies a field strength limit of 10,000 uV (10 mV) per meter at 30 meters from the antenna. In practice this works out to 1.8 mW transmitter output power into a 1/2 wave dipole, or 3 mW into an isotropic (0 dBi) radiator. While this power level may sound minuscule remember that by comparison, only a fraction (< 1%) of the power a 100 mW Part 15.219 AM transmitter feeds to its antenna is actually radiated by even the most 'efficient' 3 meter antenna; in fact, the amount radiated is roughly comparable what is permitted in this HF band

Lowfer is good for part 15 to

Longwave Part 15 stations operate under the provisions of 15.217 which permits 1 watt final input power, and an antenna, feedline and ground lead combined length (not height) of 15 meters (~49.2 feet) maximum. All LF systems known to the author use an antenna, which may be any of various types but usually are the typical vertical monopole, either a mast/tower or a "flattop" (wire "T" as used by aviation LF beacons) and with radials and/or a ground screen. The 160-190 kHz band is often referred to as "the 1750 Meter Band

Some unfortunate realities here are that propagation loss over the surface of the earth is very high using of a wavelength of 22 meters. Groundwave coverage of compliant 22-meter Part 15 systems would be worse than Part 15 systems using 540-1700 kHz, under 15.219.

And even if the skywave produced by a 1/2-wave horizontal dipole radiating 1.8 mW plus a 100 % ground reflection was 100% reflected from the ionosphere, the field strength that system could produce over a total path length of 200 km would be around 2 µV/m. Probably not "broadcast quality."

Finally, except for ham radio operators and a few others, there would be no radio listeners with a suitable receiver and antenna system for 22-meter Part 15.

This post is not intended to discourage experimentation, but to show what performance such systems might produce.
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"The lack of experimental broadcast stations operating here is truly amazing, considering the relatively generous field strength allowance and great (world-wide!) propagation in this frequency range. This Part 15 band is available in the USA and Canada for use by people like us: hobbyists, low-power radio and broadcast enthusiasts, and experimenters..."

"Here is a shot of the Wentzel I built for shortwave running on 13.56. It is crystal controlled and runs very nicely with good audio. It was fairly easy to build on perf board and worked right off the bat. My tank coil needs to be improved a bit as I experimented to find the right combination..."

A bit more info about alternate approaches is on Jon Smick's legendary http://home.att.net/~weatheradio/part15.ht m" target="_blank">Part 15 site here:

http://home.att.net/~weatheradio/HFtransmit.ht m" target="_blank"> http://home.att.net/~weatheradio/HFtransmit.htm

However, the link to the oscillator test page noted in Jon's writing is obsolete. The new location for the oscillator test page is here:

http://www.mlecmn.net/~lyle/epson/epson.htm

And what do you know, but Lyle's reference to the Epson site is also 404, but I found a current copy here:

http://www.eea.epson.com/portal/pls/portal/docs/1/503460.PDF

Lyle provides additional transmitter info here:

http://www.mlecmn.net/~lyle/proto/LFproto.htm

Then there is this interesting piece from a completely different source about using crystal oscillators in AM broadcasting, modulating with a transformer, here:

http://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html

Note that the Smick/Koehler unit is CMOS, while the Sci-Toys unit is TTL

Experimental broadcasting for a better tomorrow!

If someone was using a part 15 Sw tx that was compliant, how many miles could their signal reach? It sounds like an intresting subject.

Travis

Hams use the 20 meter band for DX (long distance) operations. The 22 meter band is close enough to the 20 meter band that the characteristics are essentially the same.

Local point to point communication on the 20 meter band is not what it is about. My experience is with 280 watts PEP on SSB and 20 miles is about it and that is where both stations have good antennas and receivers. It is probable that the local range of such a part 15 transmitter and antenna would be comparable to what we have in the AM broadcast band. It would be great if someone who uses this band (and I know you are out there) could comment on their experiences for local coverage. The "magic" of 20 meters comes from the skip or reflection off the ionosphere and not the groundwave propagation. I have worked world wide on this band.

Hams operate what is known as QRP (low power), sometimes involving only milliwatts of power and make contacts thousands of miles away. This is not the norm but it can happen.

As Rich pointed out earlier here, who will be listening? Perhaps if you establish a beacon with CW ID 24/7 someone might come across your signal and QSL (acknowledge receipt).

These are just some of my random thoughts on the subject but I hope they put it into perspective.

Neil

Perhaps if you establish a beacon with CW ID 24/7 someone might come across your signal and QSL (acknowledge receipt).

Great idea, and I happen to have the stuff I need laying around my mess at home to set that up. Probably be VCO, but I have a freq counter so...

Unfortunately I'm in a terrible location (Pacific northwest, so I'll be transmitting to the Pacific ocean), but that's just the way it is.

More as I

Experimental broadcasting for a better tomorrow!

I had forgotten that RHC uses the 22 meter band.

Lot's of good stuff on the web site,

http://www.radiohc.org

including this simple transmitter project, which would need a modulation section for broadcast use.

http://www.radiohc.org/Distributions/Dxers/ultra-simple-transmitter.html

Experimental broadcasting for a better tomorrow!