how can add antenna be used for both rx and tx, and how can rx and tx be amplified?

It would be much simpler to improve the beam shape of the antennas, to confine more of the energy to the path between the two antennas.

I agree.

Increasing the transmitted power won't gain you much unless you _significantly_ increase it (inverse square law) which is why we have made most improvement in receiver sensitivity in the RF world for the last few decades. That ignores using DSP techniques which are a different subject.

Unless you have the transmit/receive signal coming out of the unit you won't be able to run your amplifier anyway, and even then you would need a good T/R switch (Macom makes excellent PIN diode switches, of which I use some).

Shaping the RF radiation pattern is much simpler to do.

Cheers

PeteS

I agree ! To add an amplifier for transmit or receive you have to get behind the antenna switching circuits. At 2.4Ghz it probably uses a circulator and that is going to be power limited !

The thing is - I have unlimited (ok within reason of course) power available - so I figure why not use it?

So the way tx/rx antenna sharing works is by using a T/R switch? I expect I'd be able to crack open the module and hijack that signal from the other T/R switch, don't you think?

Not when you have no idea of where one module is with respect to the other!

-Mike

I'm sure that's true - but I don't have any idea where one device is with respect to the other. So I don't think I can do too much to improve the beam shape, can I? I'm working on putting GPS devices on both ends (currently one end already has GPS) so that I can actually aim directional antennas - but that's still in the future.

-Mike

Hi Baron - if it matters, it's operating at 433MHz.

-Mike

Not always. Some items use a diplexer to separate the signals.

A pair of Yagi antennas pointed at each other will do more that hacking the equipment.

Of course - but that would require me to know where the two modules are with respect to each other - and I do not know that as one of them is mobile.

So? That only makes it slightly more difficult. A fixed antenna, along with the Yagi, a small rotor and use the signal level to track the other antenna. Or break down and spend the money for a pair of sat terminals so that you can talk to each other anywhere in the bird's footprint.

Ahh ! Inside the amateur 70cms band. In which case you may be lucky if it uses a relay to switch the antenna. You will need to break out the TX line to feed a linear amp. Just watch the power rating of the relay. As far as the receiver is concerned, you need to improve the noise margin without adding too much gain. 5 or 6 Db should be more than enough. Noise figures for a front end should be around 1.5Db or better. A Yagi antenna will provide both gain and directivity more cheaply than either of the other solutions though !

I didn't know that when I wrote the previous post. In that caseyou are going to have to use co-linear antenna. You will get 6 to 7.5 Db of gain with those.

The module's I'm using don't give any sort of feedback about signal strength. The only way I know I have a signal is if valid data is coming through.

How difficult would it be to figure out signal strength? Methinks probably fairly difficult.

-Mike

Not really. Its only as hard as you want to make it, like every other thing in life. If you want to do the job, you find a way. Locate the IF amp and tap into it. If you can't find the AGC circuit you can feed a small sample of the IF signal into one of the chips made for cell phones with a RSS output. Amplify it if needed, and use it to control the motor drive. Tube car radios tuned for maximum signal strength in the late '50s, with just a handful of extra parts. Look up "Wonder bar". You should be able to do better than a 50 year old design without breaking a sweat.

In article , snipped-for-privacy@gmail.com (known to some as Mike Noone) scribed...

Just an FYI -- The ARRL Antenna Book will probably have lots of useful info on duplexers and antenna design overall. Should be readily available from your school's library or arrl.org.

Happy reading.

Well, a diplexer combines (or splits) two signals but in the same 'direction'. I've used waveguide duplexers in the past.

Most consumer type equipment now uses T/R switches as they're smaller and cheaper.

As to the original question, there's no way to know how it was done without having the module; and even then the switch may be embedded within a custom mixed signal device.

Cheers

PeteS

I can see a couple of problems here:

If you can only increase the transmit power at one end, then you will only improve the situation in one direction. Adding a receive amplifier probably wont help you much unless the existing rx amp has a very poor noise figure.

I don't know what country you are in but here, and in most other countries, there are some quite specific regulations on what frequency and power you can transmit, and for what purpose. If you increase the transmit power you may be breaking the law, and the penalties can be quite harsh.

Yes, seeing the device makes it easier to reverse engineer. I have a pile of 433 MHz diplexers from cordless phones, and have worked with UHF TV diplexers at commercial TV stations, rated up to 200 KW input. (Over a half ton of brass and copper. Copper pipe on the inputs and rectangular waveguide on the output.) :)

Just plug a yagi (or other high gain antenna) into where the existing one attaches.

Bye. Jasen