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The RF Workbench / 11 meter beacon project - 1kHz tone on CB CH 23 - 27.255 MHz 27255 kHz
« on: January 09, 2016, 1905 UTC »
[Scroll to the bottom to see current on-air status]
I'm working on this project with another operator, who wishes to remain anonymous. So far, two versions have been built. Mark I, on 27.500 MHz (crystal controlled), transmitting a continuous tone. Power output is 80mW. Mark II has a crystal holder provision built in so frequency can easily be changed by changing crystals. Currently have 26.540 MHz, 26.995 MHz (CB channel 3A, an allocated R/C frequency), 27.090 MHz, 27.185 (CB channel 19) and 27.545 MHz crystals available. Mark II power output is around 1W, which can be used to drive an amplifier (during testing this produced just under 50 watts). Transmission is a continuous tone in AM mode. The Mark II transmitter uses a modified 27MHz R/C controller transmitter. Antenna is a dipole roughly directional to NE/SW.
Testing with Mark I on 27.500 with 80mW on the dipole has produced a range of around 1 mile in an urban area during the daytime (band open and noisy). 27.500 is the unofficial "beacon" frequency for the 11-meter freeband. Mark I is currently not on the air.
Frequency choice is likely to be 26.540/26.995/27.545 due to heavy use of 27.185 (CB channel 19 - the trucker/road channel), 27.090 being right next to CB channel 11 (27.085) which is another very active frequency during band openings. 26.540 is likely to be clear, as is 27.545. 26.995 has an advantage of being within the legal CB band, however there is risk of QRM from Part 15 and Part 95 users (remote control, other low-power data usage, etc). I feel that 26.995 would attract the least amount of attention from the authorities.
Transmitter is not under continuous operation at this time, however I am creating this thread to create awareness of this project - which is still on-going. Version III will likely support a CW ID keyer instead of a continuous tone like Mark I and II.
Testing will begin on 27.545 01/09/2016, alternating between 1w and 50w power levels as I test the antenna system. Signal is heard in AM mode but can be easily tuned in SSB/CW mode.
As of 1950 UTC 03/20/2016 the beacon is on 27255 (CB channel 23) at 1w. Antenna is attic-mounted, facing NE-SW. Turning on the amplifier causes all sorts of issues - SWR on antenna system jumps from a 1.3:1 to 3:1! The antenna is cut for 27000 but I'm seeing a SWR of 1.3:1 on the lowest (26540) and highest (27545) frequencies available to me at 1w power levels. I'm guessing this could be due to the whole setup (transmitter + amplifier + tuner) all being right next to the antenna and RF getting into all or some of those components. More testing is needed (or I need to get an amplifier that isn't as powerful).
As this is a work in progress, I will eventually be looking at the signal on a spectrograph display and seeing how wide this signal really is.
EDIT 01/11/2016 2200ish UTC:
Beacon is back on the air, center frequency set at 27545 kHz, signal is roughly 10-15 kHz wide. Power is 5 watts into a vertically polarized antenna (for this phase of testing 01/11/2016.) We're still not 100% sure if this is an AM or FM signal, because the tone is more "natural" sounding when tuned in FM mode, on both 27540 kHz and 27545 kHz. Transmitter is now driving a Thunderbolt 50 amplifier producing 5w into a magnet mount CB antenna that is currently sitting on huge steel piece of HVAC ductwork in the attic. Should be a sufficient ground plane (SWR reading is the same as the dipole). For local testing, it makes more sense to use the same polarization the receiving antenna uses (vertical). Will be switching back to horizontally polarized 1/2 wave dipole shortly.. Local tests using the mag-mount were very disappointing. Signal lost around 2/3 of a mile away from TX location. Switched back to dipole (what good is 4w more of power if the antenna sucks?).
EDIT 01/12/2016 1300 UTC:
Mark II is back on the air. 1w into a 1/2 wave dipole. Tone-modulated signal roughly 10-15 kHz wide centered on 27540 kHz +/- 5 kHz for drift.
I'm working on this project with another operator, who wishes to remain anonymous. So far, two versions have been built. Mark I, on 27.500 MHz (crystal controlled), transmitting a continuous tone. Power output is 80mW. Mark II has a crystal holder provision built in so frequency can easily be changed by changing crystals. Currently have 26.540 MHz, 26.995 MHz (CB channel 3A, an allocated R/C frequency), 27.090 MHz, 27.185 (CB channel 19) and 27.545 MHz crystals available. Mark II power output is around 1W, which can be used to drive an amplifier (during testing this produced just under 50 watts). Transmission is a continuous tone in AM mode. The Mark II transmitter uses a modified 27MHz R/C controller transmitter. Antenna is a dipole roughly directional to NE/SW.
Testing with Mark I on 27.500 with 80mW on the dipole has produced a range of around 1 mile in an urban area during the daytime (band open and noisy). 27.500 is the unofficial "beacon" frequency for the 11-meter freeband. Mark I is currently not on the air.
Frequency choice is likely to be 26.540/26.995/27.545 due to heavy use of 27.185 (CB channel 19 - the trucker/road channel), 27.090 being right next to CB channel 11 (27.085) which is another very active frequency during band openings. 26.540 is likely to be clear, as is 27.545. 26.995 has an advantage of being within the legal CB band, however there is risk of QRM from Part 15 and Part 95 users (remote control, other low-power data usage, etc). I feel that 26.995 would attract the least amount of attention from the authorities.
Transmitter is not under continuous operation at this time, however I am creating this thread to create awareness of this project - which is still on-going. Version III will likely support a CW ID keyer instead of a continuous tone like Mark I and II.
Testing will begin on 27.545 01/09/2016, alternating between 1w and 50w power levels as I test the antenna system. Signal is heard in AM mode but can be easily tuned in SSB/CW mode.
As of 1950 UTC 03/20/2016 the beacon is on 27255 (CB channel 23) at 1w. Antenna is attic-mounted, facing NE-SW. Turning on the amplifier causes all sorts of issues - SWR on antenna system jumps from a 1.3:1 to 3:1! The antenna is cut for 27000 but I'm seeing a SWR of 1.3:1 on the lowest (26540) and highest (27545) frequencies available to me at 1w power levels. I'm guessing this could be due to the whole setup (transmitter + amplifier + tuner) all being right next to the antenna and RF getting into all or some of those components. More testing is needed (or I need to get an amplifier that isn't as powerful).
As this is a work in progress, I will eventually be looking at the signal on a spectrograph display and seeing how wide this signal really is.
EDIT 01/11/2016 2200ish UTC:
Mark II is back on the air. 1w into a 1/2 wave dipole. Tone-modulated signal roughly 10-15 kHz wide centered on 27540 kHz +/- 5 kHz for drift.
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