300MHz RF module

[bananasiong]

The selectivity of the receiver is too poor? Oh no, this is the only type of RF module available here.

EDIT: The rfc is not being center tapped, but it center taps the coil on the PCB.

 

[audioguru]

The selectivity of the receiver is too poor?

The crappy receiver has only a single tuned circuit. It has only a single transistor which might be in a lousy regen circuit. It is a very cheap circuit.

A real radio has many tuned circuits and transistors or an IC.

 

[Hero999]

Who cares?

It's good enough for the job it was origionally designed for, to switch a relay on when it recieves a signal. Unfortunately it probably isn't good enough for what you want to do. Perhaps you should consider buying a module designed for data transmission.

 

[bananasiong]

I think this module can be modified for data transmission, but I've tried building a few PCB, they didn't work. I thought I can make it without any problem, because I don't want to use the RF module straight away.

This is the only RF module available here. I've found from Malaysia's website, there're good RF modules, work at 433 and 8xx MHz. Then I need to ask someone to order by credit card for me , and they are not cheap too.

 

[bananasiong]

Hi,
i found this, max7030, can I use this to transmit and receive digital signal? Is the value of the crystal oscilator critical? Or can I replace with some other value? How about the ceramic resonator? I thought the center pin connected to ground, then the rest can be connected either way, but there are 'in' and 'out' in the datasheet.
There is no trimmer capacitor, can this work well? I thought the stray capacitance on the PCB can affect the operating frequency?

https://www.electro-tech-online.com/custompdfs/2006/12/MAX7030.pdf

Thanks

 

[audioguru]

The MAX7030 looks like a nice modern tranceiver IC. It might be a nightmare to get a prototype to work. It would be best to buy a module that is manufactured to work well.

 

[bananasiong]

Hi,
Do you mean, it is too difficult to make one using max7030? Or this is impossible for me? Or I have chance to make one? Or it is a very very scary nightmare?

BTW, the external components determines the operating frequency right? But I see the inductors are not handmade, just wonder if it is working. Then why maxim manufacture this product?

Thanks

 

[audioguru]

An expert might make 5 prototypes before it works well, then goes into production and makes many all the same.

You aren't an expert with VHF and with surface-mount parts so maybe you must make 10 or more prototypes before it works. When it doesn't work then you don't have the skills and the test equipment to find out why not.

 

[bananasiong]

Make a number of prototypes? What is their different? Placing of components?

 

[audioguru]

Stray capacitance might cause the first ones to oscillate.
Stray inductance might cause the next few to have low gain.
You might have some prototypes that oscillate and have low gain.
Many parts might need their values changed to compensate for stray capacitance and stray inductance.

It would be a frustrating challenge to make one that works.

 

[bananasiong]

Wow, challenging, need to spend much time for this. Anyway, how far is the transmission?

Thanks

 

[audioguru]

It is designed for keyless entry for cars (and the car talks back?). The keyless entry RF system for my car has a range of about 20m but the transmitter's antenna is too small for better range.

There must be a ham radio operator around here who can calculate the range for you when the conditions are perfect.

 

[Hero999]

Build it as small as possible, use SMT parts for all of the componants, even the inductors.

 

[bananasiong]

I haven't involved in SMT before, maybe this is the time for me to try the first time.

 

[bananasiong]

Oh, I couldn't get surface mount component here. Only one shop has it, but only certain value of resistor only, they don't have capacitor....

 

[Hero999]

RS Components sell SMT resistors, capacitors and inductors.

 

[bananasiong]

Hi,
Sorry for pulling up this thread, but I have some question. The 'crappy' RF module that I mentioned before, is that FM or AM? I compared it with the mod4, the signal goes in to the base which the transistor is oscillating at its collector. So is it FM?

Thanks

 

[Hero999]

Like the mod4, it produces both AM and FM. The amplitude changes as the transistor's gain is altered be adjusting the base current as does its capictance which changes the resonant frequency.

 

[audioguru]

The 'crappy' RF module that I mentioned before, is that FM or AM? I compared it with the mod4, the signal goes in to the base which the transistor is oscillating at its collector. So is it FM?

The Cmos oscillator in the transmitter turns on and off the RF oscillator transistor at about 4kHz. So the carrier is amplitude modulated (AM). It is very over-modulated so it must create a lot of interference.

The receiver looks like a super-regenerative piece of junk that also is AM.

 

[bananasiong]

OIC, thanks.
How about this,CC1000 from Texas Instrument, is it very difficult to make one?
https://focus.ti.com/docs/prod/folders/print/cc1000.html

Or it is as difficult as MAX7030?