Rf receiver, transmistter 30.875Mhz

[smitchel]

Hi everyone,

I'm trying to find a diagram for a RF receiver and transmitter on the 30.875Mhz frequency, I have found the diagram of a 433Mhz transmitter here **broken link removed** and I was wondering if this schematic would work if I replaced the 433 crystal by a 30.875, or if there's some sort of mathematic behind that needs all the components to be recalculated.
As for the receiver diagram, I don't know where to find one, but if anyone has an idea, please tell me.

Thank you in advance for your help.

 

[cowboybob]

If I may ask, why 30.875MHz. specifically?

That aside, yes, you would have to change the vaules of other components, most notably the inductors (other components have no value listed in the schematic you posted).

You might consider a simple "transceiver" instead, since elements of such a device serve both transmit and receive functions.

 

[4pyros]

If I may ask, why 30.875MHz. specifically?

That is the same as some garage door openers.

 

[smitchel]

Yes indeed it is for a garage opener.
Thank you for your answer but I still don't know how to get the diagram I need to make the device.

 

[4pyros]

Yes indeed it is for a garage opener.
Thank you for your answer but I still don't know how to get the diagram I need to make the device.

What do you want your device to do?
Turn something on and off or transmit data or voice???

 

[cowboybob]

What do you want your device to do?
Turn something on and off or transmit data or voice???

As 4pyros points out, the particular schematic you posted is for sending some manner of data (if used as a door opener) in that the "data" line is for turning on/off the oscillator in a digital pattern (an opening or security code). Of course, the data line could also be a simple on/off signal as well.

To modify the transmitter circuit, as it is, you might want to use this site (for starters, anyway) to determine the changes you need to make to accommodate the 30.875MHz frequency change:

https://electronics-diy.com/calculators.php

Play with this a bit until you get what you're looking for, then move on to the receiver.

Without knowing your level of understanding or your access to alternate parts, this seems to me to be a decent starting point.

You might also consider downloading one of the many Simulator software options to experiment with the design/modifications of oscillators (receivers as well).

 

[smitchel]

So it's not for transmitting voice, only data, a few bytes, address, data and checksum.
I understand what you said cowboybob to calculate de component, but what diagram should I use for my pair receiver and transmitter? Is the diagram I found any good for my goal?
Also, you've talked about Simulator software, do you know any good freeware that I could use to do my tests?

 

[cowboybob]

So it's not for transmitting voice, only data, a few bytes, address, data and checksum.
I understand what you said cowboybob to calculate de component, but what diagram should I use for my pair receiver and transmitter? Is the diagram I found any good for my goal?
Also, you've talked about Simulator software, do you know any good freeware that I could use to do my tests?

The circuit you've chosen will perform (as a transmitter) as you wish, once configured for the frequency you've chosen.

The receiver I'll leave to you to find, at which point its configuration can be discussed.

The members of this forum generally prefer Spice types for SIM work, available here: https://www.linear.com/designtools/software/?gclid=CJLZpL2z8rMCFQWnnQodbUMANw#LTspice' or here: https://pspice.en.malavida.com/.

There are others as well.

Take your pick.

 

[4pyros]

So it's not for transmitting voice, only data, a few bytes, address, data and checksum.

If this is the case then why dont you use an off the shelf product opperating in the right band?
It maybe illegal to use that frequency for data and you may get interference every time someone opens their garage door.

 

[MikeMl]

Building a receiver is three-orders of magnitude more complicated than building a transmitter. You can buy ready-to-go 433MHz data link transmitters/receivers for a few bucks.

 

[cowboybob]

Building a receiver is three-orders of magnitude more complicated than building a transmitter. You can buy ready-to-go 433MHz data link transmitters/receivers for a few bucks.

I'm with Mike on this one.

Admittedly, an attractive project for a "seasoned" tech-head with a roomful of parts (and an adequate retirement arrangement) crying out to be used, but, in this case...