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I am currently working on a direction finder project for rf signals. I am attempting to use a phase detector chip to compare phases and calculate the direction. The main problem I am experiencing atm is getting the signals into the chip. I was hoping to find a reciever chip for the 433.75Mhz range. However all the ones I found included a demodulator which would mean the loss of the carrier signal (needed to compare phases). Has anyone come across an IC that can recieve the signal, amplify and filter it without demodulating it?

My other thought was that a using two basic rf reciever (not sure if it is fm or am) with an audio would work as the phase detector chip can work at low frequencies. I am not sure this is correct though as would the rf reciever mix with crystal meaning that the two signals would end up being forced into the same phase?

Many Thanks

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  • \$\begingroup\$ It may be hard to find that in an IC, something like an RF front-end LNA may be available... If all you want to do is receive 433, make a basic 1 or 2 transistor receiver with passive filtering? \$\endgroup\$ – MadHatter Nov 10 '15 at 16:19
  • \$\begingroup\$ @MadHatter I actually have tried this, I found I was able to get the signal I wanted, unfortunately my PCB happens to pick up unwanted signals, I am looking into stopping that alongside possibly finding a suitable IC \$\endgroup\$ – Stuart Rayner Nov 10 '15 at 16:52
  • \$\begingroup\$ Is your PCB inside of a metal enclosure? That is needed for most RF circuits, even if you have an IC. \$\endgroup\$ – MadHatter Nov 10 '15 at 17:10
  • \$\begingroup\$ The great thing about demodulation is that the phase is retained and then you can sample with higher granularity \$\endgroup\$ – johnnymopo Nov 11 '15 at 5:01
  • \$\begingroup\$ @johnnymopo won't the demodulation put the data into digital form? or do most fm recievers demodulate to an audio signal? \$\endgroup\$ – Stuart Rayner Nov 11 '15 at 10:39
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There are few transceivers that can output the down converted and sampled I and Q signals. With those you can do phase detection.

[Edit] One such transceiver is the CC1200 from TI.

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  • \$\begingroup\$ Any ideas what these may be? \$\endgroup\$ – Stuart Rayner Nov 11 '15 at 9:46
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A straight down-converting mixer would do the job - a number of manufacturers have them:

Linear Tech

Texas Instruments

Analog Devices - This range even includes the LO in some parts

I know that Linear Technology and TI do demonstration boards at a reasonable price that could be used as the basis of a set-up.

Phase information is not lost in mixing, so this could solve your problem.

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