Left Coast Political Scene

Transceiver Architecture 2.10 How to Build a 11.5 MHz Crystal Filter Method #1: Simply Purchase four 11.5 MHz Crystals at the cheapest price you can. Next build a Ladder Filter using five coupling caps of the same value. For a SSB Filter use 68PF and for a CW Filter use 470 PF. A guess at the in/out impedance would be in the neighborhood of 150 to 200 Ohms. Use 200 Ohms, as a 50:200 match is just a 4:1 transformer.   With this method you rely mostly on luck. It will probably not work too well. However if it does then you should immediately go out a buy a single lottery ticket as you are on a path to striking it rich.   Here are the shortcomings of Method #1. With only four crystals and making no measurement of their actual frequency you will never know: 1) how well matched they are in frequency 2) what is the filter center frequency and 3) the actual Zin/out. Did I also mention that if you don't test the crystals in an oscillator circuit pri...

Transceiver Architecture 2.09   Dual Conversion Band Switching  In this posting I want to talk about some of the specifics of the band switching and how to cause the proper Band Pass Filter and Low Pass Filters to be put in line for the band in use. The Arduino Mega 2560 The first realization I had with the dual conversion multi-band approach was that you needed a lot more pins. There will be those who immediately jump up and say but you can add a pin expander to the standard UNO, Nano and/or Pro-Mini and no need to move up to the larger footprint and more costly microcontroller. There is another requirement that is answered by the Mega 2560 and that is the 10X increase in program size. That perhaps is the bigger driver for the Mega 2560. Undoubtedly there will be more things you want to add to your homebrew rig and then pins is not the issue but programming space will be. The Mega 2560 has 54 digital pins and 16 Analog pins and thus you have many more options availabl...

Transceiver Architecture Part 2.08 The "Math" of the Frequency Display! Don't you just hate it when you see information without detail and much like the guy at 1600 Pennsylvania Avenue you hear 'Folks You Will Love This". But it still leaves a lingering question --just how did we get here and how do you insure this is not Fake News!   In our last posting we advanced the idea that with dual conversion this presents some unique problems because of the frequencies involved and how to accurately display the true transmitted frequency. Essentially we have about five frequencies we must deal with in our display process --and that is just for SSB. By way of recap we have the incoming frequency, then the 1st mixer which is the tunable Local Oscillator (LO) followed by the fixed frequency 2nd mixer and then the two BFO frequencies that address either USB or LSB.   Mind you this is Pete's scheme -- there are obviously others and better ones. BUT I underst...

Transceiver Architecture 2.07 So How to Get the Display To Read Right! 4-26-2017 Update Thanks to Addi dc0dw , here is a link that explains about interrupts. This actually makes sense. LINK There is a caution here in that the 328 (internal structure and wiring) is different from the 2560 and that is why I was having problems. But a really good treatise on interrupts. 73's Pete N6QW 4-25-2017 Update Get Your Heart Racing! --Here are some screen shots of the DifX Dual Conversion display. When you shift from USB to LSB the Display changes by 3 kHz. The current processor is an Uno or Nano but because of the pin limitations I can only support 7 bands. I have loaded the code on a Mega 2560 and am able to have 15 bands. But I am asking for some help with the Mega 2560. While I can get the bands to change and USB/LSB to change and the TUNE function and S Meter to work. The Encoder is Dead In The Water. Evidently there is a different code set to make the Mega r...

4-13-2017 ~ A small Radio story. Last evening (4/12) my XYL and I went to our favorite Chinese restaurant. Great food and really reasonable prices. As we walked in the door we saw a large party of about 25 people who were celebrating a birthday. I noted an older gentleman seated at the head of the table and our booth must have been only about 5 feet away. I leaned over to another gentleman sitting closely to me and inquired if it was a birthday celebration. He responded back that it was his father-in-law who turned 97 that very day.   I wished the celebrant a Happy Birthday and then commented to the other gentleman that his father-in-law experienced the evolution of radio broadcasting, the stock market crash, the end of prohibition, the New Deal, completion of Hoover Dam and the SF Bay Bridge, WWII, TV, space travel and the computer revolution. With that there was a bit of a buzz at the table as the other well wishers suddenly grasped what this man had seen.   Then ...

Transceiver Architecture 2.06 So What Would You Do If You Were the Designer? OK! OK! Not everyone is a rig designer and there probably are far more hams who are fully capable of building rigs than  than those who can design a rig from the ground up. But as hams we are all users and we can certainly articulate what we would like to see in a rig.   Even more so today as the new technology available to us for literally pennies, can  bring a whole new dimension of features to home built rigs. While there are many builders who like analog VFO's and homebrew dial mechanisms, there are many of us who want digital VFO's with their high accuracy and amazing stability. Many of us also like the colorful displays where lot of information is readily displayed--with much of it being in real time. Thus designs must be flexible so all quarters can participate in the project.   So as users we can influence what we want to see in a rig and in effect become the...