2m Receiver Idea

Perfect Ivan. I might test it with a diode ring mixer. 60MHz is the perfect IF as 12MHz XTAL phase modulated with reactance modulator > 74HC04 / 14 squarer + BPF > 60MHz NBFM output to mixer for up conversion to 2m band. I ordered Si5351 board for $8 online. Got a few spare arduino nano. No 2m activity is my city. I'm designing it for US hams. RDA5807 greatly simplifies the receiver section. It's maximum RF input is +10dBm. Nice dynamic range!

dare4444 wrote:Thanks for your reply Ivan.
Mixer would take in 144 - 148 MHz , mixed with Si5351 VFO of 84 - 88 MHz for 60MHz fixed frequency output to RX module. A NE612 should be sufficient for mixing. I think the performance would be good... and even if RX channel spacing is 25KHz, there shouldn't be a problem as the chances are very small of another transmission just 12.5KHz away from our RX frequency. Correct me if I'm wrong

Hi,
the channel spacing 12,5KHz is in the NBFM part of the band. CW and SSB segments IMHO use continuous tuning. The problem of a more coarse raster is not QRM from adjacent channels, but the impossibility to tune a station in a channel not contained in the raster. If you use a VFO in the converter and a fixed frequency of the RX chip, you will override this problem. You will set your own "channels" by control of the VFO.
The mirror frequency is far enough to be filtered off.
A mixer with higher IP3 than NE612 may be better.
Try it and you will see.

BR fron Ivan

Thanks for your reply Ivan.
Mixer would take in 144 - 148 MHz , mixed with Si5351 VFO of 84 - 88 MHz for 60MHz fixed frequency output to RX module. A NE612 should be sufficient for mixing. I think the performance would be good... and even if RX channel spacing is 25KHz, there shouldn't be a problem as the chances are very small of another transmission just 12.5KHz away from our RX frequency. Correct me if I'm wrong

Hi Dare,
the 2m band uses 12,5 KHz channel spacing. It may be a problem. The downconverter should be designed the way that mirror reception is avoided. The VFO can have a fixed frequency, so an XCO about 50MHz should do.

VBR from Ivan

I googled but I could not find any circuit.
RDA5807 is the latest FM tuner chip with 50 - 115 MHz receive capability
and different channel spacing to choose from. The lowest channel spacing is 25KHz. Can it be used to listen to NBFM transmissions on the 2m ham band? A downconverter is needed, a Schottky diode based double balanced mixer should do, and a low phase noise VFO based on si5351 chip. RDA5807 has a sensitivity of about 1.5uV .
A low noise Jfet LNA RF preamp would be needed to feed the mixer in order to overcome 5dB DBM loss.

Two Arduino Nano should take care of the programming.

RDA5807 needs very few external parts and it's dirt cheap. I'm surprised no one has used this module to build a 2m (144 - 148 MHz) receiver. Audio should sound okay with 25KHz channel setting, maybe a little low in volume. RDA5807 contains digital audio processor and noise cancellation features for high signal to noise ratio. Price in India is just $1.5 a piece.