Switching antenna between a TX and RX UHF module

[LBNote]

Hi,

I'm using a TWS433 and RWS433 low power UHF modules (I think less then .08
watt) , and want to switch a single antenna between the two using a Pic
micro. The antenna is a small rubber whip type.

I was thinking of just using a small 5v coil dil relay to do the job.

Was wondering if someone could explain to me if this was a good or bad idea
and the reasons ?

Thanks

 

[Phil Allison]

Hi,

I'm using a TWS433 and RWS433 low power UHF modules (I think less then .08
watt) , and want to switch a single antenna between the two using a Pic
micro. The antenna is a small rubber whip type.

** If you leave the Tx running it will inject like crazy into the antenna
and prevent the Rx from working.




........... Phil

 

[LBNote]

Yep,
Have got that covered. as it seems to be working fine at the moment,
I could always power it down though (if needed) at the same time I switch
the antenna over to the RX module.

Lorne...

 

[LBNote]

Umm not sure about top posting... just hit reply group.

Yeah the TX and RX are both on 433.292 MHz I think.

Ok thanks I can power down the TX, But is it ok to use a relay to switch
over the antenna ?

Lorne...

 

[Phil Allison]

Umm not sure about top posting... just hit reply group.

** Are you incapable of scrolling down ????????????

switch the antenna over to the RX module. so
a relay will couple Tx power into the input of the Rx making powering down
the Tx essential.

Yeah the TX and RX are both on 433.292 MHz I think.

Ok thanks I can power down the TX, But is it ok to use a relay to switch
over the antenna ?

** What is "a relay" ??

It helps to be precise.



............. Phil

 

[LBNote]

** Are you incapable of scrolling down ????????????





** What is "a relay" ??

It helps to be precise.



............ Phil

Is that better ?

The relay is a Omron Small Dual inline 10 pin type with a 5v 23ma coil ,
DPDT have not got the exact part number on hand sorry..

Lorne...

 

[Phil Allison]

Is that better ?

** YES !!!!!!!!!!!!!!!

The relay is a Omron Small Dual inline 10 pin type with a 5v 23ma coil ,
DPDT have not got the exact part number on hand sorry..

** The Farnell catalogue lists several high frequency relays - from Omron
and Nais.

Go have a look.



................. Phil

 

[LBNote]

** YES !!!!!!!!!!!!!!!





** The Farnell catalogue lists several high frequency relays - from Omron
and Nais.

Go have a look.



................ Phil

Thanks I think,
Look I'm no electrical engineer, Why do I need a high frequency relay ? What
happends if I use the one I've got ?

I'm just after an explanation so I know for future reference

Lorne...

 

[Phil Allison]

Thanks I think,

Look I'm no electrical engineer, Why do I need a high frequency relay ? What
happends if I use the one I've got ?

I'm just after an explanation so I know for future reference

** Can you please hold that one up close to the screen so I can see it ??




............ Phil

 

[LBNote]

** Can you please hold that one up close to the screen so I can see it ??




........... Phil

Phil,

If you could just stop being a smart arse for 1 second, I'm asking for
help and information here on this news group and all you seem to be
providing are half arsed, smart arsed comments. Maybe you don't ask many
questions on this news group, but I need to and if I don't provide enough
detail then maybe you could use your wisdom and assume or take a guess at
what I mean by a standard relay.

I'm usually a very polite person and don't mind helping others with a query
so long as they don't ask the same question a second time. I don't believe
I've done that here...

So can you help me with an answer or shall I just wait for someone with a
better more friendly attitude.

Lorne...

 

[Phil Allison]

"Phil Allison" <[email protected]> wrote in message

If you could just stop being a smart arse for 1 second,

** Listen fuckhead - you CANNOT tell me WHAT type of relay you have.

So HOW THE HELL can anyone answer your stupid question ?????????



I'm asking for

help and information here on this news group and all you seem to be
providing are half arsed, smart arsed comments.

** That is a stinking lie - you pig.



Maybe you don't ask many

questions on this news group, but I need to and if I don't provide enough
detail then maybe you could use your wisdom and assume or take a guess at
what I mean by a standard relay.

** Fools assume things , even biger fools make guesses.

Do not expect me to do either.

I'm usually a very polite person and don't mind helping others with a query
so long as they don't ask the same question a second time. I don't believe
I've done that here...

** Huh ???????????????????????????????????????????

So can you help me with an answer or shall I just wait for someone with a
better more friendly attitude.

** Why can you not simply GO GET that stinking relay and post the type
number ?????????


STREWTH !!!!!!!!



.................... Phil

 

[Phil Allison]

Wooh Up, Cool down man.

** Screw you.

Was just wanting you to be a little more polite in your answers.

** Bulshit - you wanted me to lick your backside.


I didn't know that you didn't have enough information on the

type of relay I was talking about.

** So why did you imagine I asked you to hold it up to the screen?

ARE YOU COMPLETELY THICK ??????????

For that matter I didn't know that there were that many types.

** That is what fools always assume.


BTW You do not seem to have the slightest idea about dealing with
RF circuits.


DO LOTS OF GOOGLING.




........... Phil

 

[Bruw]

Most ordinary relays have too much capacitance between their contacts for
use at UHF frequencies. This means that there will be a lot of leakage of
the signal and there will not be enough isolation even when the contacts are
open. There are special relays that are used for antenna switching that have
low capacitance AND shielding between the contacts.
However if you can put up with some loss of signal then try a reed relay as
they tend to have lower RF losses.
For low power units UHF switching transistors are often used.

In any case it is best to switch off the TX output when the antenna is
switched to the receiver. For fastest response try switching the oscillator
stage of the TX. Also when the TX is operating it will tend to leak signal
into the RX and often overloads the front end of the RX. It could take from
mS to seconds to recover. SO better to short the RX input during transmit.

 

[LBNote]

** Screw you.




** Bulshit - you wanted me to lick your backside.


I didn't know that you didn't have enough information on the


** So why did you imagine I asked you to hold it up to the screen?

ARE YOU COMPLETELY THICK ??????????





** That is what fools always assume.


BTW You do not seem to have the slightest idea about dealing with
RF circuits.


DO LOTS OF GOOGLING.




........... Phil

You know what your right Phil, I am a complete novice on RF circuits and
electronics for that matter, I'm a hobbyist and I'm not trying to hide it.
Perhaps that is the reason for the miss understanding.

Lorne...

 

[LBNote]

Most ordinary relays have too much capacitance between their contacts for
use at UHF frequencies. This means that there will be a lot of leakage of
the signal and there will not be enough isolation even when the contacts are
open. There are special relays that are used for antenna switching that have
low capacitance AND shielding between the contacts.
However if you can put up with some loss of signal then try a reed relay as
they tend to have lower RF losses.
For low power units UHF switching transistors are often used.

In any case it is best to switch off the TX output when the antenna is
switched to the receiver. For fastest response try switching the oscillator
stage of the TX. Also when the TX is operating it will tend to leak signal
into the RX and often overloads the front end of the RX. It could take from
mS to seconds to recover. SO better to short the RX input during transmit.

Arrh ok, now I know what to look for.

So I need to check the specs of my particular relay to see what the leakage
and isolation specs are for the
433 MHz band.

Thanks every so much for your answer.

Regards

Lorne...

 

[LBNote]

DID YOU NOT SEE THIS !!!!!!!!!!!

"
** The Farnell catalogue lists several high frequency relays - from Omron
and Nais.

Go have a look. "



YOU CERTAINLY DID NOT HEED IT





....... Phil

Yeah I saw it, I even went and had a look at the farnell site. But it was
the laymens reason for needing the HF relay I was after.
Thanks for your input, I'll try and be more specific next time,

Lorne...

 

[Mike Harding]

Arrh ok, now I know what to look for.

Yep, agree with what Bruw said.

Don't worry about Phil - he's our resident loonly and he doesn't
know much about RF anyway. He's probably torn his new frock
or something and is in an even worse mood than usual

Mike Harding

 

[Phil Allison]

Yeah I saw it, I even went and had a look at the farnell site. But it was
the laymens reason for needing the HF relay I was after.

** He says - moving the goalposts again and again....



............. Phil

 

[onestone]

There's no misunderstanding, Phil's the resident foul mouthed lunatic.
ignore most things he says when he gets off technical issues (most of
the time). He doesn't make the rules here regarding top posting either.

As Bruw noted conventional relays exhibit high losses at UHF, you can
use an antenna switch, specifically designed for this task. Clarke and
Severn stock them, Honeywell amongst others make them. If you can live
with the losses through a standard relay keep using it.

Al

 

[Brian Goldsmith]

As Bruw noted conventional relays exhibit high losses at UHF, you can
use an antenna switch, specifically designed for this task. Clarke and
Severn stock them, Honeywell amongst others make them. If you can live
with the losses through a standard relay keep using it.



**By his own admission (Look I'm no electrical engineer, Why do I need a high frequency relay ?) the OP has
indicated that he wouldn't understand anything about the losses you are referring to.

Brian Goldsmith.