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Filters

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M0BSW:
I've been building a bandpass filter for my amateur radio, is there a way I can check the roll off, with a frequency counter and oscilloscope, I want to use it for 5MHz band weve been allowed to use with permission, from Ofcom & MOD, and I want to make sure anything pass the upper frequency is stopped dead in it's tracks. And really not sure how to do this.

fbs:
What you want to do is measure the ratio between the input and output voltage at each frequency(step). The scope can measure the input & output voltage, but you need something to generate the input signal with.  If you dont have a signal generator a dds synthesizer might be an option. AD9850 boards are quite cheap on ebay and good for 20MHz or so.

PA0PBZ:
The filter works both ways, so you can use your receiver to check the attenuation. If your S-meter is reasonable correct you can even see how many dB's it is attenuating on the frequencies of interest.

M0BSW:

--- Quote from: fbs on March 30, 2013, 03:37:17 pm ---What you want to do is measure the ratio between the input and output voltage at each frequency(step). The scope can measure the input & output voltage, but you need something to generate the input signal with.  If you dont have a signal generator a dds synthesizer might be an option. AD9850 boards are quite cheap on ebay and good for 20MHz or so.

--- End quote ---
Hi Yes I do have a signal generator which goes up to 10mhz,so I'll use that.

M0BSW:

--- Quote from: PA0PBZ on March 30, 2013, 03:41:53 pm ---The filter works both ways, so you can use your receiver to check the attenuation. If your S-meter is reasonable correct you can even see how many dB's it is attenuating on the frequencies of interest.

--- End quote ---
,
Yes it is correct , never thought of that staring right at me, thank you, isn't it funny you look for a technical way , when the most simply and effective way is right there. :phew: Thank you fellow radio amateur :-+

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