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

[Mike Noone]

Hi - I have a wireless modem type of device that gets about 1KM range
at 9600 baud. It uses a single antenna for both receiving and
transmitting. I'm hoping to add an amplifier to this module to increase
range. Ideally I could just add both an rx and tx amplifier on one end
(as I have no power constraints on one end, but pretty serious power
constraints on the other end) - but either way.

So - I'm a senior year EE and we have done alot of work on making
amplifier circuits. But everything we've done has just been having an
input signal and an output signal - I'm not exactly sure how things
would need to be different with having signals coming in from the same
antenna as they're going out. Maybe is there some sort of switching
device on the module that switches the antenna between sending and
receiving? Or something else? Can anybody give me some guidance on
this?

Thanks!

-Mike

 

[John Popelish]

Hi - I have a wireless modem type of device that gets about 1KM range
at 9600 baud. It uses a single antenna for both receiving and
transmitting. I'm hoping to add an amplifier to this module to increase
range. Ideally I could just add both an rx and tx amplifier on one end
(as I have no power constraints on one end, but pretty serious power
constraints on the other end) - but either way.

So - I'm a senior year EE and we have done alot of work on making
amplifier circuits. But everything we've done has just been having an
input signal and an output signal - I'm not exactly sure how things
would need to be different with having signals coming in from the same
antenna as they're going out. Maybe is there some sort of switching
device on the module that switches the antenna between sending and
receiving? Or something else? Can anybody give me some guidance on
this?

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.

 

[PeteS]

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

 

[Baron]

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 ! 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 !

 

[Mike Noone]

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.

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

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).

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?

Shaping the RF radiation pattern is much simpler to do.

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

-Mike

 

[Mike Noone]

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'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

 

[Mike Noone]

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 !

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

-Mike

 

[Michael A. Terrell]

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

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


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

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

-Mike

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


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Mike Noone]

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.

 

[Michael A. Terrell]

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.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Baron]

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

-Mike

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 !

 

[Baron]

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.

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.

 

[Mike Noone]

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.

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

 

[Michael A. Terrell]

The modules 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

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.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Dr. Anton T. Squeegee]

Hi - I have a wireless modem type of device that gets about 1KM range
at 9600 baud. It uses a single antenna for both receiving and
transmitting. I'm hoping to add an amplifier to this module to increase
range. Ideally I could just add both an rx and tx amplifier on one end
(as I have no power constraints on one end, but pretty serious power
constraints on the other end) - but either way.

<snippety>

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.

 

[PeteS]

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

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

 

[Gareth]

Hi - I have a wireless modem type of device that gets about 1KM range
at 9600 baud. It uses a single antenna for both receiving and
transmitting. I'm hoping to add an amplifier to this module to increase
range. Ideally I could just add both an rx and tx amplifier on one end
(as I have no power constraints on one end, but pretty serious power
constraints on the other end) - but either way.

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.

--

 

[Michael A. Terrell]

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.

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.)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[jasen]

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

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

Bye.
Jasen