sergio

Procurei nos meus e-mails e encontrei vários links que o Carlos Carneiro da Abramulti forneceu sobre stub. Inclusive abaixo a descrição de como montar o stub:

Postado originalmente por Carlos Carneiro

Build a co-ax filter.

You can build a simple coax stub notch filter.
These are the rules.

• Coax resonance rules.
• From the T connecting point, a 1/4 wave transmission line shorted at the far end is, viewed as open.
• From the T connecting point, a 1/4 wave transmission line open at the far end is, viewed as shorted.
• The speed of light in free space is about 300,000 km/sec.
• To find wave length divide frequency in MHz/300.
• The speed of light in solid polyethylene coax is 66%, a value known a velocity factor.
• The speed of light in foamed polyethylene coax is 78%.
• Find the wavelength in coax take the velocity factor % of free space wavelength.
• Use 1/4 of this length for an open 1/4 stub notch.

For example, If we want to filter an FM station at 100 MHz = 3 meters.
We are using polyethylene, so 66% =1.98 meters.
1/4 of that is .495 meter.
I cut a length of coax .495 meter long, and leave it open at the far end.
I make a T connection, with the stub dangeling and I now have a notch at 100 MHz.
Since the notch repeats at 3/4 wave length, I also have a notch at 300 MHz, 500 MHz, and so on.

http://www.k1ttt.net/technote/K2TR_M...tter_Stubs.jpg

Links:

http://www.k1ttt.net/technote/k2trstub.html

http://theskywaves.demon.co.uk/techn...Coax_Bulan.pdf

http://www.standpipe.com/w2bri/assemblecoaxialcap.htm

http://www.standpipe.com/w2bri/build.htm

http://lists.contesting.com/pipermai...er/004317.html

http://www.ifwtech.co.uk/g3sek/swxfiltr/swxfiltr.htm