Low Pass Filter Board: Part 3

So its been a busy day here in the workshop. Caps arrived today and we set about to making low pass filters for the transmitter. I started by sticking in the caps and then in turn winding the inductors for each of the 3 filters, 80, 40 and 20m bands and giving them a test by feeding in a square wave from my it makes nice distortion signal generator.

80m Low Pass Filter Under Test

The output was fed into the spectrum analyzer on the Red Potato. The spurs either side of the fundamental are crud from my signal gen, it does that when you start to turn up the output. This was a 10 volt peak 3.6mhz square wave being fed into filter and I through up a few cursors to get some levels, first harmonic is -60dBm down on the fundamental. That should be more than good enough.

I did the same for the 40m and 20m filter, again -60db down on the first harmonic, the above image being for the 40m band.

Something I was worried about was isolation on the relays. These are no uber doober premium rf relays, no no no, they are 10 for $1 Chinesium Grade floor sweepings and seconds off Ebay. So we stick the signal in the in port and connected the 100meg Hantek scope up to the other end and turned the volts per division down to the noise floor and looked for signal leakage. Nothing, maybe a couple of microvolts but that might have been an aberration. Either way, good enough for the kinds of girls i go out with.

Final board all together and soldered up.


A bit of an idea of how its all going to go together as a stack. I think things might actually work ok after all. Touch wood.  Tomorrows job is to program an ATMEGA IC to work as an iambic keyer, add in some switching and buffering to get the transmitter up and working. Not sure if i am going to have an external PA yet, or just use a couple of BD139’s and get 3 or 4 watts out. Will see how we go.


Need A Tool-Make A Tool

I watch a bit of blacksmithing on youtube and something these guys often say when they are building something is Need A Tool, Make A Tool. Its a good way to think about life, why run to the store when you can make something now and do the job you are trying to do now.

So, with my breadboard setup, I am wanting to monitor the current demands of everything I am hanging off the one micro as it will eventually be running off solar and batteries and I need to make sure i have a few days of battery supply and enough solar to charge everything up within a days daylight. Don’t want my things turning off and losing precious data.

So i grabbed an Oled display i could not get working out of the box and got it chooching, a voltage and current sensor that i had doing nothing and made them all talk together with some software and she is skookum as frig. So all i gotta do now is wire it up with a nano stick it in a tiny box with some banana sockets and put it in between my power supply and my breadboard and I will always know how much current we are drawing.