The AR2N6 is a dual conversion narrow band FM receiver kit for two amateur bands, 6 meters and 2 meters. The kit is by Elenco Electronics, Inc. and is available from several venders. The tuning is done by controlling the voltage on a varactor diode built into the main IC with a potentiometer. The manual guides you through construction in stages with tests and calibration of each stage as you go. The manual also has a good amount of theory as to how the various stages work and even how some of the component values are calculated. All in all, it is a very educational kit.
The kit does not come with hand tools or solder, which must be supplied by the kit builder. It does come with a tuning wand for adjusting the various coils in the kit. There are procedures for testing and aligning without test equipment, but the job goes much better with some simple test equipment.
We (the local ham radio club and I) have built three of these kits so far. In all cases the parts were all present and well packaged. The PC board is solder masked and silk screened to ease construction. There are some extra holes and some missing holes that show that the kit has gone through engineering changes since the PC board was initially laid out. There are also a few minor changes to the manual in mounting of mechanical parts. It is not unusual for a kit to under go several small changes of this nature during its lifetime.
The audio stage is the stage that shows the most engineering changes to the PC board. There are three components that have to be soldered to the back side of the PC board. The first component soldered to the back side of the PC board is C2, a .005uf RF bypass capacitor that keeps the IF frequency from getting into the LM386 audio amplifier. Here is a photograph of the correct way to install C2. AR2N6 C2 picture
The next two components soldered to the back side of the board are used to suppress a high frequency oscillation that can develop in the LM386. C22, a .047uf capacitor provides a path for high frequency signals to R15, a 10 ohm resistor. By having a non-inductive load for these signals, you prevent the LM386 from oscillating at 200 KHz. This photo shows the installation of R15. AR2N6 R15 picture This picture shows the installation of C22. AR2N6 C22 picture
This is a photo of the top side of the board with the audio stage built up and ready for
check out.
AR2N6 Audio Stage Top picture
This picture shows the bottom of the board with the audio stage ready for check out.
AR2N6 Audio Stage Bottom picture
The manual has an extensive check out procedure for the audio stage. As long as you have access to an audio signal generator there is really nothing to add to what is in the manual.
Block 2 is really the 455KHz sections of the radio. The IF stage and the detector. The manual goes into fairly good detail on the quadrature detector. The DC test verifies the operation of the 5 volt regulator and makes sure you don't have any shorts in your board. The AC test uses a 455KHz signal to set L5 for the center of its operational range. I have found that a fixed frequency oscillator comes in very handy here and I have thrown one together using a 16.384 MHz crystal and a small program in a 12F629 PIC processor (an 8 pin microcontroller) to toggle an output pin at 455KHz. With a little filtering, it makes a dandy 455KHz test source. While the manual suggests lowering the signal level for testing the squelch control, I have found the squelch range wide enough that I can leave the generator at 100mv and still test the squelch.
This is a photo of the top side of the board with block 2 built up and ready for
check out.
AR2N6 Block 2 Top picture
This picture shows the bottom of the board with block 2 ready for check out.
AR2N6 Block 2 Bottom picture
The final electrical assembly is done in one marathon session without testing as you go. These sections finish the 10.7MHz IF stages, second conversion stages and local oscillator sections. The manual has you do mechanical assembly of the kit before doing local oscillator alignment, but I prefer to align the local oscillators before doing mechanical assembly because it is harder to get at the components to do alignment after the front panel is attached.
As to the local oscillator alignment, I have found that these kits tune well beyond the ham bands of 6 and 2 meters, so I try to center the middle of the ham band in the center of the tuning control range, giving a little tuning above and below the ham bands.
I have found the quickest, and easiest way to tune the local oscillators is to use a frequency counter. The 2 meter band has not really required any adjustments of the coil which is a good thing because spreading and compressing the tiny coil by hand would be a pain. On the other hand, I have had to do significant tuning on 6 meters to center the tuning, but the tuning wand is included with the kit, so adjustment is fairly easy.
This is a photo of the top side of the board with all electrical components installed and
ready for alignment.
AR2N6 All Componenets Top picture
This picture shows the bottom of the board with all electrical components installed and
ready for alignment.
AR2N6 All Components Bottom picture
You will note that not all holes are filled in. This is likely due to the board being used for various different bands in the past, some of which required differnt configurations. You will also have a 39pf capactitor left over. This capacitor is included in case the tuning on the 2 meter band is too high. If it is, you remove the 33pf capacitor and solder the 39pf capacitor in its place. I have never had to do this, but it is nice to know that it is there is case you need it.