Here's the TenTec 1220 2-Meter Rig1220 PC Board
Why Build Your Own 2-Meter Rig?
Why would anybody build a radio from a kit when you can buy one with more features already assembled for less money? If your only desire is to get on the air and communicate then I don't think I can answer that question to your satisfaction. Many asked the same question back in  HeathKit's heyday. At one time it was actually less expensive to build a HeathKit than to buy a factory rig. But that was back when most of the rigs we used were made in the USA. Now most of the HF, VHF, and UHF rigs are made in Japan, Korea or another far east country. The prices for such equipment are more attractive than ever. However, let me tell you why I decided to build TenTec's 2-Meter rig.

Getting on the air with a rig you built yourself is a thrill you have to experience to understand.
Hams from the earliest days have taken pride in building their own equipment. Of course that was often due to necessity rather than by choice. However, even when hams could buy assembled receivers and transmitters they continued building. It was a great way to learn and it was a matter of pride. Not only that- it was fun! Every ham should build some of his own equipment even if it is only a small accessory. Building a kit is by no means the same as assembling a scratch built radio but for the average ham it is an acceptable option. When I was a teenager, I enjoyed listening to hams on my HeathKit GR-64 shortwave receiver. It was the first kit I ever built; cost $37.50 and represented a lot of sweat pushing a lawnmower. My soldering was pretty lousy looking but when I finished, it worked. At night I listened to 75 meters and that's where I first heard hams who looked disapprovingly upon any amateur who used store-bought equipment. I know this attitude continues in some circles. Well, I don't think the fact that a ham builds his own gear makes him some kind of "super-ham" who can look down his nose at the rest. But, if you've never built anything how about changing that today. Choose a small project and  begin honing your construction skills.

I want to understand how my radio works. An engineer's understanding is not necessary but on the other hand I don't like operating a "black box."  TenTec has done an excellent job explaining how their 1220 works. In some ways the TenTec manual does not measure up to their old HeathKit counterparts. However, it excels in several other ways. In the back of the manual it tells you the purpose of almost every component- even resistors and capacitors and also tells you in which construction step the component is installed. For instance:

Reference       Description      Step No.    Part No.   Circuit Notes
C95                  .001uF              5-22                             RF bypass on mic input
D4                    1N4148            1-23                             blocking diode for battery backup
L16                   1uH                   4-58           21112       DC return path for T/R pin diodes
U8                     LM358N          5-2             25117       Transmit audio
Q6                     2N5087            5-3             25001       Switches U4 TX line to low from Mic PTT

TenTec's description of how the VCO and PLL work is superb and runs three pages. Here's a little excerpt from that explanation to give you an idea. Hopefully this small sample will give you a sense of the writing style used.

"...Imagine for a moment that the transceiver is completely built except for the PLL circuitry (U5, Q10-13), microprocessor and display. Imagine a simple potentiometer as a tuning control, varying the voltage applied to the cathodes of varactor diodes D7 and D8. Could we receive and transmit on any frequency we want  in the 2 meter band? The answer is 'yes -- sort of!' We certainly could receive signals loud and clear, and we could transmit 4-5 watts or even the optional 35 watts RF output, though we'd have to rig a few switches to replace some T-R functions handled by the microprocessor. However, the odds of the VCO running at exactly 10.7 MHz lower in receive are virtually nil. So, actual communications, even in simplex mode, would be unlikely, even though both receiver and transmitter 'work.' In addition, the oscillator's frequency stability will be marginal without constantly touching up the tuning control.

'Constantly touching up the tuning control' is the job of the PLL frequency synthesizer! The Motorola MC14170 PLL IC is a very recent, innovative and sophisticated device with much more capability than we need to understand or discuss. In fact, its patented 'BitGrabber'TM  technology virtually assures trouble free operation of this crucial section of the transceiver...."

Okay, I hope you get the picture. This represents only a small part of the discussion and leaves out much of the "ground-work" information that was presented earlier. All of this information when combined helps me understand how the radio works and encourages me to think that just maybe I can repair it when it fails. This leads to my next point.

I enjoy repairing my own equipment. Sooner or later if you keep a rig long enough it will break. My experience says sooner rather than later. And most factory rigs are now full of surface mount components. Like it or not, construction using surface mount devices is a fact of electronic life. Many new components are only available in surface mount packages. Fortunately, the 1220 uses conventional components with the exception of one surface mount capacitor that was easy to install.. Repairing your factory job is more than just a little intimidating for the average ham. My experience with imported ham equipment has not been particularly good. You don't have to listen long on 2-meters or HF to hear a QSO describing problems with a new or existing rig and getting it repaired. Although I'm impressed with the engineering that goes into the modern rig I am less impressed with some of the materials used in their construction. A common gripe of mine is the lousy PC board material often used in imported rigs. Good quality PC board is just not that expensive. TenTec's boards are first-class!  The last two factory built 2-Meter rigs I purchased developed several problems. Some of those problems were experienced by other owners. One of the radios had an intermittent from the day I got it. It worked most of the time but every once in awhile it would just go off into limbo. Finally, it quit completely. The Kenwood TS-440S was one of the most popular HF rigs ever built but eventually, they all develop the same problem(s). The VCO goes wack-o and the PLL unlocks. That's because the rubbery gunk they used to mechanically stabilize components in the VCO becomes conductive. If you own one you have had or will have that problem. Did you repair it yourself or will you repair it yourself. When I look under the "hood" of one of these rigs my palms begin to sweat just thinking about the damage I could do. A metal box containing several PC boards covered in surface mount components and interconnected with a mass of hair-thin wires does not encourage repair by the average amateur. When you build a rig yourself, you become familiar with how it goes together and how it comes apart. You learn the alignment procedure and where the test points are located. You know where to go for parts and you know the part numbers. If all else fails you can talk to a technician who knows the engineer who designed it. Sometimes you can even talk to the engineer.

So there you have it. I enjoy operating a rig I have built myself. I like to understand how it works and I like being able to repair it when it breaks. Hmm, let's see, what can I build next?
 
 

So how does the 1220 stack up? I have not completed the final tweaking of the radio but I have made several contacts with it and audio reports have been excellent. I'll save the final report for later. Until then, thanks for stopping by!

73,
Don  WA4IML
 

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