20dB or 40dB RF Attenuator

I have found that I need an RF Attenuator for my bench. My bench tools are primarily suited to QRP work and so whenever I have to mess with a 35W FM rig I find that my meters and sensors are inadequate. I've killed quite a few bits of test equipment by stuffing 50W of RF into a 5W power meter.

As part of a larger project to create a 0-500MHZ power meter I started with the attenuator. There's nothing special about this one other than perhaps the compact design. It can be either a 20dB or a 40dB device dictated by the resistors you populate it with. Indeed, if you buy the boards from oshpark.com you can make both variations for less than $5.

See how simple it is?

The attenuator will present a 50Ω load to the connected radio and with its 1/4W resistors should be good for small bursts of around 50W of RF. Adding 1/2W resistors should increase the power capability to 100W and allow for longer key-up times at lower powers.

The files are listed below in both Eagle and PDF formats.

20-40dB_RF_Attenuator.pdf
20-40dB_RF_Attenuator.brd
20-40dB_RF_Attenuator.sch

Credit card sized Arduino with Ethernet

I dunno about you but I find the whole Arduino board format very cumbersome. It can also get very expensive too. Frustrated with boards stacked on top of each other I decided it was time to create a smaller board format that housed my most common components: ethernet, I2C, 12v PSU and of course the micro processor itself. 

One can find anything on Al Gore's Interweb if one looks hard enough. It was not long before I discovered something that could be fashioned into use. It had a few minor issues but as I would have to design a board anyway it was a good jumping off point.

The completed board

My version differs from drj113's in that I have removed the DIP switches and replaced them with a dual header so that one can use the header for either analog inputs or as a DIP selector. I returned all the components back to normal size (some were SMD). I've also brought out all the unused digital pins to a header on the edge of the board and added a FTDI interface so that one may connect a serial programmer.

Well, it almost worked first time. I stuffed the PCB, uploaded a sample sketch that would connect to the Internet and .... nothing. Crap! I hate diagnosing circuits. But for some odd reason rather than get the meter out and poke on about the board I decided that the problem MUST be with the software. I get like that after a beer or 3.

I was kinda sorta right too! It would seem that there are in fact 2 different libraries for the ENC28j60 Ethernet chip I'm using and of course, I had the other one. Easily fixed. I edited the library source code to reflect the moving of one of the signal pins used by the Arduino to talk to the Ethernet. It appears that the 2 libraries exist because of the addition of an SD card reader. The SD card would share some of the same pins as the Ethernet. To allow for both, the Ethernet pins get moved around a bit. Great! I fixed it. Upload the sketch and ..... nothing. 

Well, not nothing but not anything useful. I had established communication with the Ethernet chip but no further. This was proved by the reading of the Ethernet chip's version number and then the failing of any DHCP. CRAP!!!!

It turned out to be a trivial fix in the end but it took me over an hour to diagnose; I had neglected to add a pull down resistor onto one of the Ethernet controllers pins. 2K7 later and bingo! It did not take long to correct the PCB files and re-upload them to oshpark for others to use.

The final board with all the bugs ironed out

I've already pressed this board into service with my NTP shack clock. It works great!!

The design files in Eagle format . . .

Ethernet controller 1.1.1.brd

Ethernet controller 1.1.1.sch

Bitx DDS and frequency display

I built a Bitx20. I'm not happy with it. The VFO leaves much to be desired and whilst many folks find it acceptable I find it cumbersome and inexact. I never know what frequency its on. It appears that many users find this to be the case as is evidenced by the handful of digital VFO addons for the Bitx. Time to build my own.

So what do I want mine to do? Well, let's see . . .

• Arduino based (because it's easy)
• LCD readout
• Use cheap Ebay 9850 DDS module 
• CW keyer with paddle input
• FT-817 style computer control
• Channel buttons
• S Meter and battery voltage etc.
• Probably other things too

And here it is! It did not take too long to create. I borrowed much of the Arduino code from  other projects and hacked it all together.

The finished board

Observant bastards will have noticed the MIC and PTT inputs on the upper right of the board. This allows the PTT from the Mic to be wired through the board. The board will then compare the current frequency against it's internal band plan and then key the rig (or not). It will also display a TX or RX symbol on the readout.

The LCD readout showing the current frequency (upper line), battery volts (lower left), step rate (lower middle) and S-meter reading (lower right) 

The board under test

The IF + VFO combined output

The files ...

avr_dds_homebrew_i2clcd.pdf
avr_dds_homebrew_i2clcd.sch
avr_dds_homebrew_i2clcd.brd
BITX30_LCD_UI.ino
BITX60_LCD_UI.ino

The packet racket

I'm working with a small group of other hams trying to get some Packet Radio links operational again. You would think that after 30 years of this mode there would be an easy, turn key method with which to get it all going. Think again.

One of Packet's problems is that it was more-or-less abandoned in the mid 90's when the World Wide Web came along. So the only stuff that one can get for this mode is of that vintage.

APRS on the other hand uses Packet Radio and is very successful. But still there are few to none turn key kits available for this variation of Packet.

It would seem that I'm not the only one thinking that this should be easier. I went looking for a TNC (Terminal Node Controller) that I could attach to the USB port of my computer. This was a mammoth task in itself. With newer machines leaving "legacy" connections behind, Ethernet and USB are the order of the day now. No more serial ports.

Then I happened upon SP9UOB's dsTNC. It is a dsPIC (a PIC that does DSP). It has all the makings of a low cost, easily constructed TNC. It can do 1200bd (the current data speed) and has aspirations on 9600bd with a firmware change.

SP8UOB's original drawing

Looks simple right? Problem is that it has a "proper" serial port. No USB.  That I can fix. I've been doing lots of stuff with the FT232 USB-Serial converter chip lately so I added on to this design.

My version of the TNC

So I then designed a circuit board. 2 in fact. One using "normal" sized components and the other using SMD parts. There were a few things wrong with it but nothing that a few "green wire links" couldn't fix.

The PCB I designed

The test board

Then came time to plug it in. The firmware has a terminal interface to aid in setting up things like your call sign and the PTT delay etc. It also has a KISS mode. I connected it to a radio and tuned to the local APRS channel. Lots of lovely APRS positions came spooling in to my computer. It works!!

But I don't want to use it for APRS. I want to use it for normal Packet operations. In support of this the device supports the KISS mode. This mode allows the user to operate the device in a manner not unlike a normal modem; the attached computer will do all the work.

It does NOT work! Well, that's not quite true. It does support KISS and works just fine if all you want is an APRS modem. But a TNC is more than a modem. It has a CPU, RAM,Modems etc. What I found was that if the passing data packets were of a certain length they would be decoded. If they were shorter or longer they would not be decoded. This is flat no use with normal Packet operations.

After much gnashing of teeth and questioning of known working equipment I tracked down the problem. The firmware was not correct. The "TNC" part was not there. 

I advised SP9UOB of my findings and he in turn sent me a patched version of his firmware. Indeed this worked - sort of. I could now decode passing data of any size but if the data was too long it would arrive garbled or even be missed altogether. SP9UOB has not selected the correct micro processor part and so it did not have enough RAM to store/decode the passing data. So it still doesn't work as I'd hoped it would. 

Back to the drawing board!

Design files are in Eagle format in case you want to have a go yourself.
dsdigi_v124.hex
dsTNC.brd
dsTNC.sch
dsTNC-smd.sch
dsTNC-smd.brd

APT weather satellite pictures

Back in the late 90's I realised a long term goal. I bought and built a weather satellite receiver. The kit was developed by a group called RIG (Remote Imaging Group) and sold for around £100. A good few thousand of these kits were sold worldwide. I even bought more of them to give away to local schools.

Its now 2014 and this kit has run its course but look closely on Ebay and you'll see that they are still available. RIG has been selling them for a closeout price of £50 plus shipping. As I had given away my last one to UACNJ I grabbed me another kit.

The finished kit in its new housing

I also made a few modifications. The kit would normally have a single 7 segment LED to indicate what channel it was tuned to. You could also add a signal strength meter to give you some idea as to how well you were hearing the satellite. I decided that I wanted a LCD rather than an LED. It would make the project look a little more modern. To that end I designed a LCD interface around an Arduino. I drew heavily from the work of Grant Zehr, WA9TFB. Grant had earlier designed a similar LCD display based on a PIC16F84 but it was limited to displaying only a few channels because the chosen PIC was lacking input and so could not read the entire state of the LED. The Arduino doesn't have that problem.

The Arduino LCD expansion board

In addition to the LCD expansion board I created a breakout board to better handle the large wiring loom that connects all the controls to the actual receiver. This board also manages the master power switch as well as supplying power to the LCD board.

The breakout board

To my surprise it all works! I've not finished putting holes in the enclosure yet but the receiver and display work very well. I have populated the channel table in the Arduino with some information about the satellite that is on a given channel so that one can see more than just "4" or "9". The Smeter is also displayed as a bar graph on the lower left of the display when receiving a satellite.

The whole project undergoing testing

Looking for satellites

The next step is to connect it up to a spare PC so that I can display the actual pictures the receiver gets. I'll make these available on my website too.

Design files in Eagle format.
AVR_LCD-I2C.sch
AVR_LCD-I2C.brd
AVR_LCD-I2C.ino
RX2 Breakout Board.sch
RX2 Breakout Board.brd

A new clock for the shack

Segal's Law states :

"A man with a clock knows what time it is. A man with 2 clocks is never sure."

It speaks to having too much information when making a decision.

I have that problem. I have a thing for building electronic clocks. Nixie's, LED, LCD, Binary, VFD. I have them all. I have never built one of my own design however. They have always been found on the Internet and built from a diagram or around a PIC etc.

This clock is different. I can honestly say that I designed it from scratch. I wanted an NTP based clock so that it would always be correct without me having to set it every time the power went out. I also wanted to learn how to use an Arduino. This clock was born out of a combination of those two needs.

In addition to displaying the current UTC time the clock also displays the current cycle of the HF Beacon Project.

I love this picture ....

I'm a member of UACNJ, an astronomy club in Hope, NJ. We are open to the public every Saturday night from April until the end of October. It was one such night last year when I took the below picture. I was standing with my back to the 'scope when I heard a child screaming. I turned around and saw this Praying Mantis on the finderscope. He was very obliging and waited for me to find my cell phone so that I could take his picture.