#Qucs low pass filter tutorial full#
#Qucs low pass filter tutorial software#
#Qucs low pass filter tutorial series#

RS, Mouser, Digikey, Farnell et al exist to save me from such pits of electronic doom, why on earth would I do anything else but buy ready-made? My revised filter circuit with off-the-shelf component values. I can wind my own inductors, but therein lies a whole world of pain of its own and I’d rather not go there. It’s an extremely idealised graph, and experience has taught me that real-world filters using these designs have a lower-frequency cut-off point, but for our purposes here it’s a good enough start.Īs previously mentioned, the component values are not preferred ones from a commercially available series, so I can’t buy them off the shelf. Plug in the required figures and it spits out a circuit diagram, which we can then simulate to show a nice curve with a 3dB point right on 30MHz.

#Qucs low pass filter tutorial software#

The filter we’re designing is simple enough, a 5th-order Bessel filter, and the software is the easy-to-use QUCS package on an Ubuntu Linux machine. The idealised graph produced by QUCS for our filter. So it’s worth taking a look at the process here, and examining the effect of tweaking component values in this way. The software calculates ideal inductances and capacitances for the desired cut-off and impedance, and in selecting the closest preferred values we modify the characteristics of the result and possibly even ruin our final filter. The results are good, and anyone can become a filter designer, but as is so often the case there remains a snag. Happily as with so many other fields, in recent decades the advent of affordable high-power computing has brought with it the ability to take the hard work out of filter design, Simply tell some software what the characteristics of your desired filter are, and it will do the rest. The 30MHz low-pass filter, as QUCS delivered it. There are tables and formulae, but even after impressive feats of calculation the result can often not match the expectation. It’s a network of capacitors and inductors usually referred to as a pi-network after the rough resemblance of the schematic to a capital Greek letter Pi, and getting them right has traditionally been something of a Black Art. Yellow usually has bad contrast to the silkscreen and you just can’t see the traces on black boards), so the boards will likely be blue.If you are in any way connected with radio, you will have encountered the low pass filter as a means to remove unwanted harmonics from the output of your transmitters. I think should take that off again, before generating the gerbers.Īlso I’m a fan of blue soldermask (green is boring, red to aggressive, white only gets dirty, On the other hand it makes the board look somehow official,which might cause some confusion, at least if I start handing out the spares to people. The idea for logo on the back since is that I’ll have to pay for the silkscreen anyway, so I might as well do something cool. Here is how a final version might look like. So as a rule of thumb I prefer to sacrifice some selectivity for more practical component values.īy the way: I made the board a few mm smaller, it’s now 76mm x 47mm so it should fit the enclosure perfectly.

#Qucs low pass filter tutorial full#

I’ve build filters using air coils for the weird inductors I got using the design tool and well … let’s just say tuning it is a full afternoon of fun for the entire family.

#Qucs low pass filter tutorial series#

Given the large amount of free space on the board it should be trivial to add some The tricky bit is finding a combination of values that work well while also being of the E series so that you can buy the components.

My plan was to leave the inductor unpopulated, but being able to enable and disable the power without soldering sound better to me. Having the diplexer/filter as separate module just provides some flexibility to pick what ever works best for given The jumper are probably a good idea. So when I’m experimenting here it is better to have the filter in front of the LNA. In that case the strong signals simply saturate you amplifier and the filter after it is basically useless. I’m currently in an urban area with strong American military transmitters nearby, On the other hand if you are in an urban area, or even worse an area with strong transmitters nearby, you’ll run into problems with this approach. Surrounded by mountains on all sides which shield it it even from the local HAM radio relays. That would probably work fine for my ground station as it is located in small village, The conventional wisdom seem to be that the LNA should ideally be placed as close to the antenna as possible and preferably before filters so it can make up for cable and insertion losses. Having the LNA on the same board is something I’ve been pondering for a while now. I’ve already using the calculator in KiCAD to get the initial parameters for the traces.