4 Band Bandpass Filter Board

The relays are double pole double throw in a standard 18x9mm package size. The transistors are anything you have in CBE footprint, I used 2n3904 and the resistor is there for current limiting, just pick a typical value, i think i used 4.8K. The trimmer caps I use are 3 leg 100pf max value to tune and align each filter.

SMA edge connectors bring RF in on the left side of the board. By default all relays are in the OFF position and no RF can pass through. The 6 pin header brings control signals and power to the board. To turn a relay on, a 5v control control signal is placed on one of the first 4 pins to turn 1 pair of relays on. The last 2 pins are ground and VCC of the relays you used.

Aligning each filter can be a bit tricky, it is best to use a spectrum analyzer and tracking generator if you have one, or a noise source and spectrum analyzer or even in a pinch if you slow down the seconds/division on the oscilloscope so you can see the filter shape. The reason being, if your filters are not quite tuned right, you will end up with 2 peaks and some attenuation in the bandpass you just do not want.

The filters themselves are Double Tuned circuits. To design the values needed for each band I used some software called DTC.exe which can be found on a CD in the book Experimental Methods In RF Design. I have linked it here for download, but I am not sure if I am allowed to and i will pull it down if asked by the authors: DTC DOWNLOAD

The gerber files for the board can be downloaded from here: Bandpass Filters

Here is a schematic of the filters with values for 80, 40, 20 and 15m.


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4 Band Lowpass Filter Board

Board Design 

Ok, in the spirit of sharing and making things easy for people, I am going to start releasing some gerbers for the various boards I have designed for my various projects, that work HAHAHA, because, yes, not everything i do works.

I am not into this for making money, I do everything that i do simply for the love of it and for the learning experience. So selling boards and things is not high on my agenda. And besides, you can get 10 boards made and send to you from JLCpcb in China for not much more than it would cost me to send you one from Australia.


First cab off the ranks 7th order low pass filter boards. So you will notice there are no part values on the boards. Why? Well because i do not know what bands you might like to build for. The relays are double pole double throw in a standard 18x9mm package size. The transistors are anything you have in CBE footprint, I used 2n3904 and the resistor is there for current limiting, just pick a typical value, i think i used 4.8K.

SMA edge connectors bring RF in on the left side of the board. By default all relays are in the OFF position and no RF can pass through. The 6 pin header brings control signals and power to the board. To turn a relay on, a 5v control control signal is placed on one of the first 4 pins to turn 1 pair of relays on. The last 2 pins are ground and VCC of the relays you used.

For designing the filters I use an online calculator like this one at Calculators Edge: http://www.calculatoredge.com/electronics/bw%20pi%20low%20pass.htm Or a software tool like Elsie.

Lowpass Filter Board

Gerber Files can be downloaded from HERE:  http://vk4ffab.info/Files/LowPass_Filter.zip


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Control Board

This is the 2nd time that i have rolled my own control board using the SI5351A. The first one was much simpler than this and had a few other bits on the board. This time around I have gone to town on features that i will incorporate into the firmware. This is why i have used the Mega, i am using just about all the IO pins on offer. 38 pins are being used for the TFT LCD display. I would have preferred to use an I2C or SPI display, or perhaps even a nextion, but they are either 2 times the price or in the case of the nextion, i would have to learn how to program it first.

I have a total of 8 push buttons or switch control lines, 5 are currently going to be used for things like band change, mode change, tx/rx switching etc. The bandpass and lowpass filters take up another 4 lines each. Yes, this is a 4 band receiver/transceiver. The IF filters will also be switchable between 2 filters, one for SSB and the other a narrow CW filter.

7 of the analog pins will be used to control an attenuator that will give the radio between 0 and -31db of attenuation and finally, we have a rotary encoder for the VFO a keyboard and real time clock. I plan to incorporate my arduino logging software into the radio to have everything in the one box.

The plan at the moment is to have 80, 40, 20 and 15m SSB and CW receiver with a CW transmitter for the same bands, with the option of using the same boards to make a SSB/CW version at a latter date.

Boards were designed and laid out by me and manufactured in China at JLCPCB This is the 2nd time i have used them for prototype boards. The first order was great, nothing wrong with the boards at all. This last lot have a lot of pads with solder mask covering parts of the pads. Nothing that cannot be fixed with a little sandpaper, but very annoying. I think the issue was due to them being rushed because of a public holiday in China. I will give them another go and if the same thing happens I will go back to using PCBWay.

I have been planing ahead for this project for sometime. I had ordered these 40pin ribbon cables on the understanding that it was row compatible for use on LCD displays. Its not, it reverses inside row to outside somehow. Anyway I got Ebay China’d on that part LOL. So I had to make one using using a bit of superglue and some female to female dupont jumpers. Its rather stiff, but will work till a new part arrives.

The new desoldering vacuum made light work of removing the female headers off the Mega, being replaced with pin headers.

 

Board layout is a skill in and of itself. Its nothing easy and something that i struggle with. But i am getting better everytime i do a board. Above you can see i added parts to the other side of the board. LOL this is a first for me and I did not stuff it up. The 5v regulator is orientated the right way. 🙂

The fun part is about to start. And that is developing the firmware to make this thing do what it is meant to do. And no, i will not be sharing my firmware. The main reason is because I do not want to have the issue of supporting it or helping people who cannot get it to work. Most of the code is already on the net. There are a dozen VFO codes already on the web, the Arduino Logger code is on my site, things like push buttons etc are easy enough to do, so anyone who is keen enough can very easily integrate these things together and make a functioning vfo, logging and rig control board.

Here is the PCB layout as it currently stands. All the connectors are 2.54mm JST-XH connectors. The SI5351A is from QRP LABS   I know you can get these also off ebay and simular places and the footprint is probably a little more friendly, but I choose to support QRP LABS when ever i can. They are a good grass roots company that has never let me down.

Gerber Files: Control_Board Use these at your own risk. At the time of posting the board was not 100% checked to see if all functions worked as designed or the layout to be suitable for any particular task. By downloading these files, you agree that you will only use them for your own personal projects and not to sell bare boards, kits or to make a commercial product with them. I call this, the don’t be an arsehole license. If you cannot agree to not be an arsehole, do not download my files.Facebooktwittergoogle_plusredditpinterestlinkedin

Rob’s Receiver Part 3: IF Amp and Xtal Filter

First IF amp and the Xtal filter is build. IF amp is perfect and works exactly as designed. The Xtal filter is a bit rough as you can see from the plots below. It needs to be a bit narrower, closer to 500hz would be nice. Its a bit ripply which is probably due to imperfect terminations and because the xtals are not very well matched, being more like + or – 300hz not 50hz. I have a better frequency counter and a couple hundred more xtals coming slow boat from China, so I should be able to improve things quite a lot when I can measure down to 10’s of hz.

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Rob’s Receiver Part 2: Band Pass Filter

Bandpass filter as designed in Elsie. In practice was a little low in frequency when built. I changed the end caps to to make them a little lower to bring the frequency up. The bandpass is rather ripply and if i remember latter I will Bode Plot it on the red pitaya.

Here is the schematic. It works but does not have the smoothest bandpass. I will see how it goes for now and if its not good enough, redesign it.

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Robs Receiver Build: RF Amp

So i have started to build the actual project now rather than build and test different blocks. Its about time that I actually built something from beginning to end. So lets start with the schematic.

A blank canvas all ready to go.

The first stage built, but not working in this photo. The J310’s i have, have a different pinout to the data sheet and i put a cap where a resistor should be 🙂

Got things fixed and working in this photo.

Maximum gain from the dual gate rf amp.

Minimum gain from the RF Amp.

So far things are going swimmingly and next job is to wind an output transformer for this stage and then start on the bandpass filter.Facebooktwittergoogle_plusredditpinterestlinkedin

IF Filter

So after building the IF Filter haphazard looking like a spastic, I connected up the test gear to run a Bode Plot to see the shape of the filter. I then proceeded to sit here wondering what i did wrong for the next hour as my 500hz CW Filter is almost 4K wide and probably ok as an AM Filter. LOL. Well, slow as slow can be it dawned on me, I grabbed 470 capacitors out of the box, thinking they were 470pf not 471 capacitors which are 470 pf. So in my haste and not thinking i have 47pf capacitors in my filter not what i originally planned.

 

On a positive note, the shape is not all that bad and not to much ripple even though the input to the filter is not correctly terminated. That is another headache, trying to get accurate measurements of in and output impedances and matching right when you have not built the preceeding stages. So I am going to switch to Termination Insensitive Amps for the IF and make my life easier.Facebooktwittergoogle_plusredditpinterestlinkedin

MPSH10 IF AMP

So i had another swing at the MPSH10 in LT Spice and what it says should happen and what actually is happening are 2 very different things. I got it sorted and it is working fine. But I am not sure if i run with this or revert back to the 2n3904. For now I will run with this and see how it goes, I just have to measure the input and output impedances. Which as of next week or so, will be easier when i have a vna. The circuit is a little different to what was in the schematic in the previous post. I will update the schematic if I end up running with these.

I build this a little different, I had these squares sitting there i made so I used them.

Oscilloscope output, green trace is the signal in, yellow signal out.

 

Output from the spectrum analyzer.Facebooktwittergoogle_plusredditpinterestlinkedin