Summer brings all sorts of wonderful opportunities. Some involve ham radio and some focus on the food consumed in the summer months. Things like watermelon and corn on the cobb or the tons of burnt burgers cooked on a charcoal grill.
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I mention foodie stuff because non-contest ham radio this weekend will be a bust with Field Day. So, if you just want some friendly QSO's forget it until next Monday.
This might be a good time, if not participating in Field Day to think about station accessories. I am often surprised that many stations do not have an in line SWR bridge. If you were smart enough to ditch EMRFD and acquire SSDRA, you can find some nice designs for homebrewing a SWR bridge.
For those who do not fear the Arduino you can do some code modification to include a Tune Up functionality built into the code. Typically, all of the code I develop has a Tune capability.
So why would you need a Tune function in your homebrew rig? One of the primary reasons is to provide a bit of RF to the antenna to assure you have the lowest SWR. Another is to determine if the rig is operating properly. Still another reason is that you are one of the cool guys who has this capability.
[For those forever welded to the Bitx design, I have always been surprised that a Tune Tone was not in the original design. In a Bitx40 I modified so that it does both LSB and USB (for FT-8), it also has the Tune Function.]
The theory of operation is simple. The Arduino is capable of generating tones using the Tone library. One of those tones is 988 Hz. So, firstly we generate a tone at that frequency, and next we set the code so that it is on for a certain time period and the off for a certain time period.
We ask the code to do this for so many cycles using a loop counter. We now have essentially created a pulse train of so many cycles, typically about 10 seconds. This pulse train is then introduced into the microphone circuit. Unless you add some isolation, you unplug the microphone and use the MOX switch as you don't want to back feed audio tones into the microphone.
Now a bit of a sewer backup. The Arduino output is like a square wave, so we need to set its level (trim pot for just a few watts) and add an RC Filter to turn those square waves into a sinewave. I think there might be some issues with harmonics of the generated sound wave if they are left as pure square waves.
Essentially an engagement of a momentary push button starts the tune sequence. Now in several of my rigs this also trips the PTT switch while in others I simply engage a MOX (manual switching of PTT in addition to the PTT on the microphone) and then hit the Tune button. The MOX approach also offers a way to have the transmitter on without having to use the Mic like for troubleshooting.
Once the 10 second sequence is over the rig goes back to receive. Now to be totally Kosher you need to station identify your station once the test is complete. OR as I did in a couple of rigs simply extended the code after the 10 seconds to send my call in CW. This also opens up the possibility of an automated station identifier as in a CW beacon.
OK wasted enough of your time so I will end this. If you want the code snippet for a Tune Tone, email me at my QRZ.com email address.
Happy Summer and Happy Burger cooking.
73's
Pete N6QW
