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I need to build a 311.2 MHz ASK transmitter to interface with a 311.2 MHz remote device. Presumably, given that this is a cheap consumer device, the modulation frequency is not too precise.

  1. Could I just use a cheap standard 315 MHz transmitter module which is off by only about 1.2%? (e.g., 315-Mhz transmitter)

  2. Alternatively, is there a simple way to "detune" the above stock module to be closer to 311.2 MHz?

  3. Alternatively, if I can't use a cheap stock transmitter, what circuit would you recommend to build one from scratch? (again this is a consumer-grade device so presumably it doesn't need to be precisely 311.2 MHz)

I am using ASK encoding to transmit the output of an MC145026 encoder. Note that this a hobbyist/consumer application -- so it can be low transmit power and the modulation frequency doesn't need to be precise or rock stable. I plan to power it from 5V USB.

I am attaching a copy of a portion of the receiver circuit that I found on the FCC website (though the quality is marginal) enter image description here

Hopefully, that can help guide on how accurate the transmitter frequency needs to be.

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    \$\begingroup\$ You need to specify many more items, including frequency stability, power level, type of modulation, environmental conditions, power sources, human interfaces, etc. etc. \$\endgroup\$ Commented Jan 27, 2025 at 21:42
  • \$\begingroup\$ Modulation is ASK as noted in the ORIGINAL post . The modulated digital signal has an underlying clock signal of about 2kHz. The frequency stability and power level is presumably equivalent to the standard cheap 315MHz consumer remotes. Power source can be 5V or 3.3V. Basically, I am just looking for a 311.2 MHz equivalent of the ubiquitous 315 MHz remote transmitters. \$\endgroup\$ Commented Jan 27, 2025 at 22:38
  • \$\begingroup\$ The ubiquitous 315 MHz remove receivers come in two varieties: crystal locked, which will not receive 311.2, (but you may be able to change the crystal) and hetrodyne, which will recive 311.2 (and may be adjustable). What is your remote device? \$\endgroup\$ Commented Jan 28, 2025 at 0:54
  • \$\begingroup\$ In what country is 311MHz a license-free band? What exactly are the band requirements in regards of channel width, power etc? Also, there is no such thing as "standard radio for xxx MHz". There's plenty of illegal, low-quality trash radio modules at Amazon and Aliexpress however... \$\endgroup\$ Commented Jan 28, 2025 at 9:58
  • \$\begingroup\$ It appears that these modules are mainly bought by scammed & confused American hobbyists but I find nothing in FCC 47 C.F.R. § 2.106 or FCC part 15 naming this a license-free band - just "fixed/mobile". So how exactly would it be possible to use in "cheap consumer electronics"? Everything I see suggests that these would be very much illegal to use in USA, which goes for anything without FCC approval no matter band. What am I missing here? \$\endgroup\$ Commented Jan 28, 2025 at 10:10

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