In article <3ec42c37-59ca-4944-97e6-1c0937ac8330@i29g2000prf.googlegroups.com>, larwe <zwsdotcom@gmail.com> writes:
>
> Yes, RF R/T switches are readily available. NEC among many other
> vendors. Very simple to use. If you look on Digikey for RF switches
> you should find many in in the sub-$3 price range (one-off qty).
> Typically they are in a SOT23-6 package.
>
Thanks. These are the kinds of things that I am looking for, but I wasn't
sure what they were called when I was looking for them, or if there were
issues with them that I was not aware of.
The comment that was made about invalidating the type certification is also
of interest, as I'm in the UK and OFCOM appear to be rather uptight about
what exactly you can and cannot do with the licence free modules.
Thanks to everyone for their replies, both here and in email.
Simon.
--
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980's technology to a 21st century world
Reply by Paul E. Bennett●January 2, 20082008-01-02
Simon Clubley wrote:
> I'm currently doing some experiments with 433MHz license free RF modules.
>
> Is it practical to share one antenna between a Tx and Rx module in a
> half-duplex environment, and if so, what techniques are used ?
>
> I would need a microcontroller to be able to switch the antenna between
> the Tx and Rx modules as required.
>
> I know that the proper solution would be to use a transceiver with Tx and
> Rx enable pins, but I am wanting to reuse some modules that I have
> available.
>
> In case it matters, this is in a hobbyist environment.
>
> Thanks for any information,
>
> Simon.
The simplest switch is either a suitable RF relay or a 1/4 wave element and
a pair of fast switching diodes in the input of the receiver. The latter
arrangement protects the receiver from the transmitter output and allows
the weaker signals for the receiver input to be seen. If you need to
transmit and receive at the same time (on different frequencies of course)
then very sharp pass-band filters for the transmitter and a sharp pass-band
and notch filter for the receiver is required.
[diagram by email]
--
********************************************************************
Paul E. Bennett...............<email://Paul_E.Bennett@topmail.co.uk>
Forth based HIDECS Consultancy
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-811095
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************
Reply by ●January 2, 20082008-01-02
On Jan 2, 7:34 am, clubley@remove_me.eisner.decus.org-Earth.UFP (Simon
Clubley) wrote:
> I'm currently doing some experiments with 433MHz license free RF modules.
>
> Is it practical to share one antenna between a Tx and Rx module in a
> half-duplex environment, and if so, what techniques are used ?
If the transmitter power is low enough that it would not damage the
receiver input, you may be able to simply connect them and de-power
the transmitter in order to receive.
However, it is possible that element in the receiver front end (such
as rectifier diodes, intentional or parasitic) might distort or
attenuate the transmitted signal. Diodes for example would likely
produce spurious emissions at overtone frequencies, which could well
be illegal. Actually the type acceptance of the transmitter is
probably invalidated if you connect anything other than the specific
antenna.
RF switches as others have mentioned are a safer if more complicated
solution.
Reply by larwe●January 2, 20082008-01-02
On Jan 2, 11:21=A0am, "Moon Shine" <msh...@msn.biz> wrote:
> How do analog cordless phones work?
> Don't they transmit and receive simultaneously on different frequencies?
If you share the antenna like that, you just make sure the filter on
the Rx will keep the Tx out of your signal. Not difficult. But it's
not what the OP was asking about. For a half-duplex system on a single
frequency (the type of device I work with mostly), simple SPDT RF
switches are an uncomplicated answer.
Reply by Grant Edwards●January 2, 20082008-01-02
On 2008-01-02, Moon Shine <mshine@msn.biz> wrote:
> How do analog cordless phones work?
Back when I worked on cellular phone designs, they use a
duplexer (a directional RF antenna coupler).
> Don't they transmit and receive simultaneously on different
> frequencies?
Yes. As do digital cordless phones and mobile phones of all sorts
(cellular and pre-cellular).
--
Grant Edwards grante Yow! I'm wet! I'm wild!
at
visi.com
Reply by Moon Shine●January 2, 20082008-01-02
"larwe" <zwsdotcom@gmail.com> wrote in message
news:3ec42c37-59ca-4944-97e6-1c0937ac8330@i29g2000prf.googlegroups.com...
On Jan 2, 7:34 am, clubley@remove_me.eisner.decus.org-Earth.UFP (Simon
Clubley) wrote:
> Is it practical to share one antenna between a Tx and Rx module in a
> half-duplex environment, and if so, what techniques are used ?
Yes, RF R/T switches are readily available. NEC among many other
vendors. Very simple to use. If you look on Digikey for RF switches
you should find many in in the sub-$3 price range (one-off qty).
Typically they are in a SOT23-6 package.
How do analog cordless phones work?
Don't they transmit and receive simultaneously on different frequencies?
Reply by larwe●January 2, 20082008-01-02
On Jan 2, 7:34=A0am, clubley@remove_me.eisner.decus.org-Earth.UFP (Simon
Clubley) wrote:
> Is it practical to share one antenna between a Tx and Rx module in a
> half-duplex environment, and if so, what techniques are used ?
Yes, RF R/T switches are readily available. NEC among many other
vendors. Very simple to use. If you look on Digikey for RF switches
you should find many in in the sub-$3 price range (one-off qty).
Typically they are in a SOT23-6 package.
Reply by Martin Griffith●January 2, 20082008-01-02
On 2 Jan 2008 06:34:13 -0600, in comp.arch.embedded
clubley@remove_me.eisner.decus.org-Earth.UFP (Simon Clubley) wrote:
>I'm currently doing some experiments with 433MHz license free RF modules.
>
>Is it practical to share one antenna between a Tx and Rx module in a
>half-duplex environment, and if so, what techniques are used ?
>
>I would need a microcontroller to be able to switch the antenna between
>the Tx and Rx modules as required.
>
>I know that the proper solution would be to use a transceiver with Tx and Rx
>enable pins, but I am wanting to reuse some modules that I have available.
>
>In case it matters, this is in a hobbyist environment.
>
>Thanks for any information,
>
>Simon.
ISTR an antenna switching scheme on the nordic semi site, but it was
for 2.4G.The site is a bit difficult to navigate.
You really need to be able to switch each module on and off quickly
via a logic input. There may be a problem of the device taking, say
100mSeconds to stablise if you try to switch the power.
You could use external switches
http://www.macom.com/psc/jsp/ListParts.jsp?dataFile=switches.txt
martin
Reply by Simon Clubley●January 2, 20082008-01-02
I'm currently doing some experiments with 433MHz license free RF modules.
Is it practical to share one antenna between a Tx and Rx module in a
half-duplex environment, and if so, what techniques are used ?
I would need a microcontroller to be able to switch the antenna between
the Tx and Rx modules as required.
I know that the proper solution would be to use a transceiver with Tx and Rx
enable pins, but I am wanting to reuse some modules that I have available.
In case it matters, this is in a hobbyist environment.
Thanks for any information,
Simon.
--
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980's technology to a 21st century world