[OFARC] band pass filters - a little theory

[Ralph (home)]

The team that planned on doing JOTA for the scout camp at Navasota has
experienced some problems.  Some members need to attend a funeral on
Saturday.

So, I have to be at the scout camp on Saturday instead of the club meeting.

 

I thought it appropriate to provide some notes for the band pass filters.

1.        I have bagged up capacitors and antenna connectors for 20m and 40m
filters.  (4 of each band)

2.       One of the 40m stays at my house for me

3.       One of the 20m bags does not have antenna connectors …. It is for
Lee.  He has a 20m filter that just needs capacitors.  The rest of the
filter is there.

4.       The selection of capacitors changed and new HF versions at low
price are available.  $5 per filter

5.       Antenna connectors were $5 for each filter

6.       Rusty has the box with capacitors and some wire if you need wire
for the coils. 

7.       I have included a print out of the schematic and parts list for
each type of filter (4 copies for each band)

8.       The printout tells you how much wire you need

 

 

A little theory on RF filters…….

High pass filters use a capacitor and inductor (or resistor) selected so the
circuit is “tuned” to have high resistance to low frequency waves and low
resistance to high frequency waves

Low pass filters do the same, only have high resistance to high frequency
signals

Band pass filters use a combination of high and low pass filters calculated
so their envelopes overlap in the range of frequencies you want to pass

 

The frequency at which the resistance goes high is called the “cut off
frequency”

 

Our project uses capacitors and inductors (coils)… not resistors

 

 

High pass filter

 



 

Low pass filter

 



 

Passive Band Pass Filter

The cut-off frequency or ƒc point in a simple RC passive filter can be
accurately controlled using just a single resistor in series with a
non-polarized capacitor, and depending upon which way around they are
connected, we have seen that either a Low Pass or a High Pass filter is
obtained.



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/ofarc/attachments/20171019/83d8a2e9/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.gif
Type: image/gif
Size: 4214 bytes
Desc: not available
URL: <http://mailman.qth.net/pipermail/ofarc/attachments/20171019/83d8a2e9/attachment-0003.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.gif
Type: image/gif
Size: 4379 bytes
Desc: not available
URL: <http://mailman.qth.net/pipermail/ofarc/attachments/20171019/83d8a2e9/attachment-0004.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image003.gif
Type: image/gif
Size: 4595 bytes
Desc: not available
URL: <http://mailman.qth.net/pipermail/ofarc/attachments/20171019/83d8a2e9/attachment-0005.gif>