Plenty of people have reviewed the 706. But they never take you on a tour of the inside! We'll, we're going to fix that. This is K9EQ's review of the Icom 706 from the inside out.
First, let me start by telling you what I like and what I don't like about the radio.
Pros:
A lot of features for the price! We're talking operation on all amateur bands from 160 through 2 meters plus 70 cm on SSB, CW, AM, RTTY, and FM. And it's not too bad a radio either. The speech processor is pretty good. The receiver is not bad. Audio from the built in speaker is quite adequate. The user interface is pretty good considering the limited number of buttons and knobs, but you'll need to sit down with the manual to figure it out. I installed the 350 Hz CW filter and it works well.
I use the 706 with an AH-4 tuner and it's great. I can operate anywhere from 80-6 meters with a push of the button and I'm able to hold my own in pileups and contests.
Cons:
Don't buy this radio because it has a DSP. The DSP is of little or no value. The only time I use it successfully is when there is a carrier on channel and I'm trying to listen to a SSB signal. The noise blanker is better than the Icom 735, but that's not saying much. My FT-990's noise blanker leaves the 706 in the dust. The fan kicks in from time to time while receiving. In a quiet room it is annoying. Don't plan on operating CW without adding a filter. There are no bandwidth filters options for the DSP (the one thing the DSP would probably be good at).
Operating Experience
I consider the FT-990 to be one of the finest radios ever produced. For 95% of my contacts the 706 works just as well as the 990. The 990 shines over the 706 when:
I have pulse type noise (see comments above about the noise blanker), there is a lot of QRM on the band, or when I need that last 0.5 dB to get through that pileup. The 990 is certainly a lot easier to operate and under contest conditions, I prefer the 990's simplicity of operation.
Would I recommend the 706? Yes, in a flash.
So, now that we're done with that, let's do what most reviews don't do - let's take a look at the inside. Click on any of the thumbnails on this page to view a larger image. Use your browser's back button to return to this page. Note that most of the pictures are on the order of 400 kilobytes. I chose to use high resolution digital photography so that you could see the details of the construction.
First let's take a look at the front of the radio. The radio is sitting on a Samlex SEC 1223 23 amp switching power supply.
The front panel is removable and allows the radio to be remotely controlled. The microphone can either be plugged into the bottom of the front panel or into the rear of the radio.
The RF connector on top is for 160-6 meters. The connector on the bottom is used for 144 and 440 MHz. The AH-4 automatic tuner plugs into the narrow rectangular connector at the bottom. Also shown is the accessory connector (you can access almost anything you need), the full size CW key connector, power input, microphone, and speaker. Note the heat sink. Air from the fan exits the radio here. Keep that in mind as we'll examine the airflow through the radio as we continue with the tour.
This is a view of the bottom of the radio.
Air enters the radio via the grill (located towards the control panel). Air enters here, is passed over the control and RF circuitry. One thing to note is that it while the radio is very solid with its construction, it doesn't take a lot of screws to remove the cover. In fact you can completely disassemble the radio in about 5 minutes after a little practice.
This is a view of the top of the radio with the cover removed.
The back side of the filter board is seen at the top of the image. You can see the fan in the center-right. The bottom board contains most of the RF circuitry. The optional 350 Hz filter is installed under the flex cable. The frame is cast aluminum. This reduces weight while providing better thermal conductivity. Note that there are not many interconnects between the boards. I really like this! It makes it easier to remove boards and increases reliability.
This view shows the top of the radio with the filter board removed and folded over on top of the RF board.
Note the thermal fins cast into the chassis. The RF amplifier board is on the back side of these heat fins. You can see how the fan takes in air (underneath and at the bottom of the image), blows it over the heat fins and exhausts it to the rear. The fan does an effective job of cooling the radio. The colder air cools the more sensitive RF and digital components first. It is then exhausts past the filter and RF stages and out the rear of the radio. While it's almost impossible to block the rear vents, be careful not to block the air intake holes on the bottom of the radio!
Let's now take a look at the bottom of the chassis.
The PA is located at the top of the image. There are three output transistors (all the same type). The one you can easily see is for 144 and 440 MHz. There are two more output transistors (under metal shields) for 160-6 meters.
The board at the bottom of the image contains additional RF circuitry.
Now let's pop the cover off of the back of the control panel. This radio is designed for manufacturability. It only takes two screws!
In this image you can see the display controller and CPU. The main tuning rotary encoder is under the metal shield on the left. Note that the interface connector on the rear panel does not take any assembly or wiring. This is an excellent example of one of the techniques that Icom used to reduce the cost of the radio while improving reliability.
Lastly, here's a side view that shows the serial label and the compression and beep/side tone adjustments. (Why they are not digital adjustments like the rest, I have no idea).
It is interesting to note that many of the calibration points of the radio are adjusted digitally via the front panel. Looking at the internal photos, you'll notice that there are not many adjustments for such a complex piece of equipment. Things sure have changed since the Collins S line!