R
Rob
- Jan 1, 1970
- 0
Hi to all.
I am trying to make a shielded enclosure to test 403 and 433Mhz
transmitters and receivers.Low power stuff(few mW) .Garage door openers
etc.
I have put a xmtr in a die case aluminuim box( 12 * 6 * 3 cm) , With no
openings. I got
pretty good attenuation of the signal. I am using the Micrel MICrf011
receiver chips , and using the AGC as a basic signal strength meter.
Seems to work ok. With the box closed tight I could only just detect the
signal.
I now needed to bring some wires into the box to supply sepperate power ,
turn on buttons etc. I have brought the wires into the box via a DB9
connector (male) mounted in the side of the box. The box has been machined
to only just fit the connector.(tight fit).
With this arrangement quite a lot of RF got out.
The wires are obviously acting as antennas and bringing the signal out of
the box.
I then put(soldered) 100pF surface mount caps from each used pin to the
chassis of the connector , which is in contact with the metal box.I did
this on both the male(machined into the box) and the female ( used to
attach wires).
The signal was attenuated quite a lot , but not enough for my liking.
I tried earthing the box , no difference. I get the feeling that would not
make a difference anyway , as a long wire (1M) to earth is a fat inductor
at 433Mhz. Tried taking the negative of the xmitter cct in the box to the
chassis , made thing worse I think :0(
Is there much more I can do , or am I barking up the wrong tree entirely!!
Any help would be appreciated.
Cheers
Rob
I am trying to make a shielded enclosure to test 403 and 433Mhz
transmitters and receivers.Low power stuff(few mW) .Garage door openers
etc.
I have put a xmtr in a die case aluminuim box( 12 * 6 * 3 cm) , With no
openings. I got
pretty good attenuation of the signal. I am using the Micrel MICrf011
receiver chips , and using the AGC as a basic signal strength meter.
Seems to work ok. With the box closed tight I could only just detect the
signal.
I now needed to bring some wires into the box to supply sepperate power ,
turn on buttons etc. I have brought the wires into the box via a DB9
connector (male) mounted in the side of the box. The box has been machined
to only just fit the connector.(tight fit).
With this arrangement quite a lot of RF got out.
The wires are obviously acting as antennas and bringing the signal out of
the box.
I then put(soldered) 100pF surface mount caps from each used pin to the
chassis of the connector , which is in contact with the metal box.I did
this on both the male(machined into the box) and the female ( used to
attach wires).
The signal was attenuated quite a lot , but not enough for my liking.
I tried earthing the box , no difference. I get the feeling that would not
make a difference anyway , as a long wire (1M) to earth is a fat inductor
at 433Mhz. Tried taking the negative of the xmitter cct in the box to the
chassis , made thing worse I think :0(
Is there much more I can do , or am I barking up the wrong tree entirely!!
Any help would be appreciated.
Cheers
Rob