Tiny Fm Crystal Receiver

[johntrk]

Hello to all.
I made an rx unit for TA31136 frontend.
Attached you can find the PCB.
Take a look pls and write your comments.
Filters(CF,CD) and crystal(35mhz) are top side.
Everything else bottom side.
Values Can be taken from TA31136 PDF(google for it)
Thank you

[quax]

Hi johntrk,

I think, that the rc crystals are made for overtone oscillation. Therefore I expect, that a LC has to be added as it is suggested in Figure 3 on page 4/16 of the PDF.

But I'm not very sure :confused:

quax

[thanhTran]

How good is this RX? what's the range that it can use?
Thanks
Thanh

I like the fact that I don't need coils. I'm afraid of those :)

[johntrk]

I didn't test it yet . I am waiting for my new oscilloscope to start testing.
based in my gws receiver the crystal with 2 caps is ok as local oscillator.
Any suggestions would be great.
New pcb with one error corection.
Eagle Pcb also included.

[thanhTran]

any chance you can post a schematic? I see several different schematic when searching for TA31136. I can't see the schematic from the PCB

Thanks

Thanh

[chaitanya]

Usually the crystals above 45MHz are operated in 3rd overtone thats because the Quartz wafer becomes very thin at higher frequency and is hard to manufacture so for this ckt at 35MHz fundamental mode should be okay, and no coils should be required in the oscillator ckt.

[jeffs555]

In general, most crystals above about 25mhz are overtone crystals, and require an LC circuit for proper operation. It is difficult to find fundamental crystals above 30mhz. Here is a good article about crystals, which says that 35mhz rc receivers use 3rd overtone crystals. http://www.favonius.com/soaring/crystals/crystals.htm

Jeff

[plane_spotter]

Have a look at Bruce Abbott's web page. He has a drawing of a GWS rx.

http://homepages.paradise.net.nz/bhabbott/circuits/GWS_4P.gif


Should be good to cross reference.

[thanhTran]

thanks very much plane spotter :).
Maybe I can just buy a dual conversion rx and add the PIC smart decoding to it :)
Thanh