tunable RF transmitter using AD9851+Arduino

[Mozee]

Hello guys (and girls if any) !!

I am trying to build a tunable RF transmitter using the AD9851 module which frequency is controlled by an Arduino. Sorry for the hand drawing in the attachment but this is what I tried building and It worked, well, sort of, but It transmitted a 12MHz wave (SW band) and I was able to hear the channel using a normal handheld radio set on receiving SW bands where the antenna is so long(In meters).

Problem is
1- Much noise is in the transmission, how to remove it?
2- Low power, how to increase it?
3- I used the toroid and a LAN wire (the single core wires which have many colors found in any LAN cable) forming 12 turns on one side and 3 turns on the antenna side, what would be better to use?

What I actually want is to build a frequency controlled transmitter which is able to transmit a clear audio for about  1Km on any wave band that might suit me but let us focus on FM and SW wave bands (Mhz range)

Any Ideas are so much welcomed

[Bandit327]

hello ,

experments are great , but your end game is not.   there is no band out there legaly that want or lets you TX music for your liking in the range your talking about. at home for around the house GREAT ! low power small range, these are great projects to learn about the fundemtals of RF, but please be aware that just because your generator says EX. 14Mhz does that mean your not throwing multiple harmonics possibly interfering with important frequencies. now that that's out of the way , there are a lot of great reads out there . as far as noise goes , you need to . have antenna tuned to the freq. you want to . your circuit has to have bypass for signal return to ground.  playing with a tunable type output (inductor or capacitor) not over driving the transistor ect.  picking the correct transistor for these frequencies. anyways keep playing around  , but the best sources are books. ebays a great place to find them cheap. radio reference books by rca , arrl , or any arrl books related .  also alot of online pdf stuff out there as well.
tip. ebay is a great place to find great scores of related parts for your builds, or junk radios to scrap for parts.

www.talkingelectronics.com     great site that has alot of projects for small transmitters , and 100s of others you can learn from .
best regards

[Richard Crowley]

In the United States, "Part 15" of federal law Title 47 regulates "unlicensed broadcasting".   Here is the Wikipedia summary...

Unlicensed broadcasting
On the standard AM broadcast band, transmission power is limited by 100 milliwatts of DC input power to the final RF stage (with restrictions on size, height and type of antenna), or, alternatively, under 15.221, if the AM transmission originates on the campus of an educational institution, the transmission can theoretically be any power so long as it does not exceed the field strength limits stated in 15.209 at the perimeter of the campus, 24000/fkHz µV/m.

Unlicensed broadcasts on the FM broadcast band (88 to 108 MHz) are limited to a field strength of 250 µV/m at a distance of 3 meters from the antenna. This is roughly equivalent to 0.01 microwatts.[2] Emissions must be kept within the 88.0 to 108.0 MHz band under Part 15 rules.

Unlicensed broadcasts on the TV broadcast bands are prohibited, except for certain medical telemetry devices, wireless microphones, and other "low power auxiliary" stations with an output of 50 mW or less. 87.5 to 88.0 MHz is considered part of the VHF TV low band (channel 6 analog audio is on 87.75), though it shows up on most FM tuners. For TV, 15.241 and 15.242 deal with high VHF (channels 7 to 13), 15.242 also deals with UHF (band IV and band V).
Ref: https://en.wikipedia.org/wiki/Title_47_CFR_Part_15#Unlicensed_broadcasting

And, just for clarity, unlicensed transmitting in ANY OTHER radio band is completely prohibited.  You may get away with it, but it is no more legal than breaking the speed limit, etc.

[ogden]

Any Ideas are so much welcomed

You possibly can use this: https://www.tindie.com/products/spaelectronics/dsp-pll-fm-transmitter-module-usbaux-in-100mw/

It's your responsibility to ensure that what you do is legal in your area. Note that 1km range cannot be achieved legally on ANY radio band:

https://www.youtube.com/watch?v=Lgu89x98PEY&feature=youtu.be&t=45

[ericj]

Experiments that defy norms are good. Experiments that are ignorant of norms are not. Generally, the best parody singers are accomplished singers in their own right. They understand the norms and understand how to convincingly portray failure.

You need to do some reading. Invest a little money in a copy of Experimental Methods in RF Design now published by ARRL and available from them directly or from Amazon. Virtually ALL your questions will be answered in very down-to-earth language with relevant circuits of interest to RF experimenters.

I've always called EMRFD and LTSpice an EE in a Box.