In the past year members of part15.us, acting as a design committee, designed a part 15 compliant shortwave transmitter under the project name "Big Talker". The two final circuit versions can be seen here:
http://www.kdxradio.com/bigtalker.html
Perhaps this information could be added to the Library section of this site, since it is a community project and not "owned" by one person.
Big Talker was specifically designed for 13.560mHz for two reasons:
1.) Part 15.225 gives this particular frequency the highest power allowance of any shortwave frequency;
2.) An important output filter is part of the circuit, and is specifically designed for this frequency.
Now it's time to build Big Talker 2, looking at the second most generous shortwave frequency range in terms of allowed power, defined in 15.227:
Operation within the band 26.97 - 27.28mHz
(a) The field strength of any emission within this band shall not exceed 10,000 microvolts/meter at 3 meters.
Interestingly, this frequency band lays upon CB channels 1 to 27, allowing either transmitting on actual CB channels or, in between certain CB channels where some extra space exists.
The main design challenge will be designing an output filter for the specific frequency of operation, or some kind of flexible output filter that can be adjusted over this entire range (26.97 - 27.28mHz).
The same circuit used for the first Big Talker can be employed by changing the crystal and output filter. Most likely the "PhilB" Version is preferable, because it produces a lower range of RF power suitable for this project.
Output filter suggestions are welcome.
So what's the point when the band is already a license free band and you can run 4 watt radios?
Will there be a massive audience flocking to that band trying to pick up a 10 thousand microvolt signal...or will the few left die hard CB'ers track you down for clogging up their yick yack channel with stuff that should not be on the band to begin with?
I'm just trying to understand the purpose of putting programs on bands that no one tunes to except for the minority die hard DX'ers. Besides that, your 10,000uV signal ain't gonna put much of a dent in the band's already cluttered mess of skip and static where even 4 watts can barely break through.
I like to experiment around too..but the band your talking about is somewhat useless for broadcasting programs...even to yourself via a wire strung across the room, unless tin can sounding music is your thing.
RFB
If philosophy were the guiding standard for part 15 radio there would be no low power radio stations.
Even with an AM station with an effective vertical/radial antenna system, the signal loss passing through housing material is only one absurdity popping the bubble of public service idealism, the second reality being the mass disinterest of the general public in either AM radio or, very likely, in the particular blend of programming offered by a particular station.
People's attention is facing a screen, whether it be a wide flat-panel or a tiny hand-held.
The need for sound is mostly satisfied by pocket mp3 players with 100 favorite songs.
Broadcasting on a frequency "no one listens to" is what we do.
Big Talker 2 will not be stopped. It is an unrealistic, pointless, and meaningless pursuit, and is in search of an output filter.
Since you'll be operating in the Citizens Band, will the Big Talker 2 fall under Part 15 rules or CB rules?
CB rules prohibit broadcasting, Part 15 has no restrictions. But, CB Walkie-Talkies, toy variety, carry the Part 15 rule notice. Hmmmmm, another oxymoron?
Cross-breeding an oxy with a moron definitely gives the situation found by comparing the CB rules: in the Rules Part 95 (26.965-27.405), with Part 15.227, governing operation from 26.86-27.28mHz.
The difference is in power, possibly also in modulation, but I'm not sure, but of course the real oxymoron is found in the contradiction between "programming (broadcasting) and non-programming".
10,000 microVolts-per-meter/3-meters probably amounts to 1mW input to the final, or something very small.
Probably a CB antenna could be used for 15.227, as there is no restriction on antenna type.
As RFB said, the signal penetration on these frequencies isn't very effective, even at 4-Watts, so the Part 15 thing is total toy.
CB service is for 2-way radio.
Another distinction: 2-way vs. 1-way.
And a guess says that even if a station was sending programming on 26.975mHz, CB channel 2, at the part 15 level, I think a CB exchange would cover it up completely and not receive it as interference.
I was just curious as to how/if the CB rules could/would apply when operating in that band.
As pointed out CB is a two-way service in which broadcasting, especially music, is prohibited. You are not even allowed to transmit beyond a set period of time.
But, then again there are other "services" within the CB band such as RC models, wireless PC keyboard/mouse adapters, etc. So, exceptions are apparent.
"even if a station was sending programming on 26.975mHz, CB channel 2, at the part 15 level, I think a CB exchange would cover it up completely and not receive it as interference."
If it is received at all, which is doubtful.
RFB
"then again there are other "services" within the CB band such as RC models, wireless PC keyboard/mouse adapters, etc."
Ya..ever see someone's RC plane come crashing down due to a CB transmission from a beefed up rig off a Raker antenna pointing in the direction of the RC airfield?
Or loose control due to the plane flying a bit too far and the skywave noise takes over and SMASH!
That's why most of those things you have mentioned have moved to far better frequencies away from that Cluster Buster band.
RFB
But all this discussion about these frequencies that are covered by Part 15 Rules is always interesting, and many of us have not explored this territory before.
The 2nd harmonic for 13.56mHz is at 27.120mHz, on a blank space right between CB channels 13 & 14, and when I first built that transmitter a buddy of mine was able to copy the harmonic on channel 14 for about 2-blocks.
I think I added better harmonic suppression.
FCC 15.227 might have some use for sending data or remote commands.... at least we know it is there and have Big Talker 2 as the means of exploiting it.
"FCC 15.227 might have some use for sending data or remote commands.... at least we know it is there and have Big Talker 2 as the means of exploiting it."
Well as far as control and command functions, I would rather play around in the 2 or 5 Ghz band. Heck anything above 30 Mhz would be preferable!
Even the digital RC remote controls had problems in the 27Mhz bands, all of which were the same as their analog counterparts, just too much skip noise which varies greatly from day to day. Plus less chance of a base station or trucker with a 1KW linear wiping out 5 channels on either side of their operating channel!
Heaven forbid either of those are running SSB!!
Might want to look around within a 2 mile radius of your location to see if there are any CB base stations, especially those using Raker beam antennas! Trust me...one of those even at 4 watts will clog up to 2 channels either side of the one your operating on. And if your going to send a 10k uV signal in between CB channels, you will want to make sure that signal does not have very far to go to reach the receiver, 5 or 10 feet is the most I would trust it at, especially if it is a command and control signal!
"Good morning..this is no name radio broadcasting on a new frequency and transmitter located 1.5 miles from our studio, bringing you....(remote transmitter begins to turn on and off from modulation from the following)
"ssssssss..breaker 19.5...breaker 19.5...east bound and down and looking for the Kojack with the Kodak report..and what's all this no name radio on the channel! Someone call the FCC..wait, I better turn off my linear!..10-10".
RFB
That is funny but sobering, RFB.
So maybe... just maybe... the Big Talker 2 needs to take a dive.
I don't know.
Life is a box. There's no chocolate.
Well there may be some use of that band for the Part 15 world.
Perhaps it could be used for a VSH link. (Very Short Hop).
Something like an ENG link to the backyard when your hosting a BBQ party and airing the festivities live on your stations. Save from running wires across the lawn making everyone even more tipsy topple weeble wobble.
Shortest RF link I ever seen was at WBAP, where the studio and TX were in the same building and to prevent ground loop and all kinds of other problems, the station used a VSH microwave link (7Ghz) with a separation of only 10 feet between the TX dish and the RX dish.
RFB
So there was this guy who designed
a transmitter that you screamed into
as loud as you could.
And that's where the power to run the
transmitter came from. The audio went
into some kind of efficient transducer,
it got rectified, and the small amount
of voltage/current generated - powered
an oscillator. It was a one transistor
thing.
It was just for fun. (The screaming voice
probably went farther than the RF signal.)
I say the same thing about Big Talker TOO.
The fun is trying to run the thing at really
low power - figuring out the output network,
etc. And figuring out what to use it for,
well - to me that's fun, too.
Maybe the fun would be in seeing how small it
could be. And I'm not engineer, but maybe this
version for 27 MHz wouldn't need the buffer stage.
I guess this thing is under Part 15.227, like
all of the other little 27 MHz doohickees (huh?)
that transmit a short distance.
Regular CB radio used to be under something called
Part 95, I think - but I'm not sure if it still is.
Best Wishes,
Bruce, DOGGRADIO STUDIO 2