Thursday, January 30, 2014

The QRP Diaries #4 - AGC for the X1M

Anyone thinking of purchasing an X1M QRP radio needs to join the YahooGroup. This is by far the most active YahooGroup / email reflector that I've ever been a member of.

The group started in March of 2013, and less than 1 year later there are 750 members, and 500-700 messages per month of activity.

AGC for the X1M

Dale Parfitt , W4OP was an early adopter of the X1M radio and took it upon himself to remedy the radios lack of automatic gain control.  For the newbies, that is the radio feature that tries to balance the volume levels of different signals. In Amateur radio imagine two guys talking on the same frequency. One is operating at 100 watts and the other at 1000 watts. Your roughly in the middle and listening to both. This experience is like standing between two people talking to each other, one is whispering, and the other is yelling.

From Wikipedia...Automatic gain control (AGC) is a technique found in many electronic devices. The average or peak output signal level is used to adjust the gain to a suitable level, enabling the circuit to work satisfactorily with a greater range of input signal levels. For example, without AGC the sound emitted from an AM radio receiver would vary to an extreme extent from a weak to a strong signal; the AGC effectively reduces the volume if the signal is strong and raises it when it is weaker.

The AGC SMD kit for the X1M was originally created by Dale and was designed to be extremely small and fit inside of the X1M , Dale designed and sold the kit in it's first iteration, and then moved onto working on a crystal CW filter KIT, also intended to be an internal board upgrade for the X1M.

Charlie , W5COV then picked up the reigns of the AGC kit and starting in Dec of 2013 was taking orders for it online. For this $12 little kit he used the same boards and parts as what Dale included in his kit. You can check it out in the Photos and Files section of the YahooGroup for more information.

I personally ordered the AGC kit before my X1M had even landed on my door step. Conversations on the YahooGroup gave me enough of a warning that is was a 'must have' mod if you could do it.

Earlier this week a tiny little package arrived in the mail, at first I wasn't sure what it was. When I opened it up, I was a little surprised at the size. A tiny circuit board the size of a nickel, and some small components. At closer inspection most of these parts were the size of a sesame seed, they had some plastic packaging around them since they were cut right off a reel of SMD parts.

I work for an electronics manufacturer, we have our own SMT line so I'm familiar with the tiny parts that the pick and place robots pull off the reels and place on the boards. In our line we move the circuit boards through in this order.

  1. A screen printer puts the solder paste on the pads throughout the circuit board. All the tiny pads get solder, the rest of the board is left clean. When completed a conveyor moves the board to the next machine.
  2. The next SMT machine places all the small SMD parts on the pads. This machine has lots of reels of parts. The multiple hands, and fingers in the machine (those are my terms, not official SMT speak) can place about 100,000 parts per hour. When completed a conveyor moves the board to the next machine.
  3. The next pick and place machine has less reels, but specializes in larger parts. The type of products we build require some larger components, it's not all tiny SMD sized parts. When completed a conveyor moves the board to the next machine.
  4. The final machine is an oven. In our case it's a 4 zone convection oven. A 'recipe' is made for each type of product to bring it up to temperature, just enough to properly melt the solder paste and fix the SMD parts to the circuit board. But not too much to damage the parts large or small. When completed a conveyor moves the board to a quality control station.
  5. Our SMT staff check the board, inspect the parts, and in some cases use a special cutter to split larger circuit boards into the small ones we would fit into our products. It's more efficient to make larger boards that consist of many smaller ones, that way more product moves through the line with less adjustments to the equipment.

So why all that level of detail?

  1. I think it's pretty cool and not everybody get's to see how stuff is made.
  2. To put into perspective the size of the parts that came in this kit.

SMD sized Capacitor - The actual part is smaller than a grain of rice, more like the size of a sesame seed.

So when I opened the kit and saw the parts I must admit I panicked a little. I built my first thru hole electronics kit only one month ago and I thought that was a size of part at the edge of my eyesight and dexterity.

So for this kit I cheated.  I know my soldering skills are C+ or B at their best. But when you work for an electronics manufacturer and your best friend works on the hardware side of R&D, you can cheat and take it to Dave.

So after hours I gave it to Dave and in less than 15 minutes he scanned the diagram, put it under his microscope and soldered it all together, I was reading the instructions and skipping ahead just to keep up with him.

His comment when it was all done "I wish we still used these sized parts in our SMT line, they're so big and easy to work on".

Dave's Work - Nice job Dave!
So knowing that the rights tools make a big deal I brought the X1M into work and over the lunch hour snuck into the lab and installed it. I was feeling a bit guilty for using Dave and I figured with the right tools I should be able to complete the job myself. Four precise solders later I was done.

AGC Kit wired into the radio and tested. Fixed into place with double sided tape
Now I sitting back at home in the shack, tuning around on 80m and WOW what a difference, all the audio so far has been very balanced, a very nice improvement!

Thanks to Dale W4OP for the great design, 
and Charlie W5COV for keeping the kit alive.

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