The IC-706Mk2G has two IF frequencies, I tapped the 1st IF at 69.0115MHz (the 2nd IF is around 9.0115MHz) and used a PAT (Panoramic Adaptor Tap) high impedance buffer amplifier designed by David G4HUP, G4HUP has different models of his PAT board and the one used for the IC-706Mk2G is the PAT-70M, the 70M means the output LPF (Low Pass Filter) is set to 70MHz, ideal for an IF around 69MHz.
IF Tap Location and Installation
I originally tried tapping the IF at L511/C512 which is before the 1st IF filter (FI511) but I found this had a number of problems;
- The RX sensitivity dropped a number of dBs, which it was not supposed to happen as this is a high impedance buffer amp and should not impact the RX sensitivity.
- There were lots of oscillator artefacts (harmonics) in the SDR display
I then tried a second IF tap point, this time it was after the 1st IF filter and so the SDR only displays a limited amount of spectrum. I tapped at L512/R513/D502 and at this point the issues from the original tap location went away, albeit with the limited bandwidth, I left the SDR PAT connected to the second IF tap location as it works for my use.
IF Tap PCB Location
The location of the IF Tap point is on the main board, which is located under the top panel (the one with the speaker in it), to the left side of the radio with the LCD facing you. Note you will need to remove the bottom panel also later on.
The Final IF tap point at L512/R513/D502 is on the front left of the main PCB as shown below;
Once I found where to connect the IF Tap to, I used some RG-178 coax to connect that point on the PCB to the PAT board. I good bit of soldering skills are needed, note the coax shield is soldered to the inductor can.
Close up of the IF Tap point showing the centre of the RG-178 coax connected to R513 (marked 331).
PAT Board Mounting
There are a few ways to mount the PAT board. Dave G4HUP can supply mounting kits for various radios for a small fee.
I simply used some back to back sticky tape which was attached to the underside of the PAT PCB and then the PAT PCB was stuck down on to the installed optional narrow filters I have fitted in my IC-706Mk2G.
If there are no optional filters then the PAT PCB could be mounted on the shielding can to the left of the current PAT mounting location shown in the images.
Rear Panel Connection
As this is just a buffered IF tap, I use phono connections for the IF output from the radio, this is used on all my IF tap modifications. I used to use SMAs in the past but SMAs became cumbersome for something where loss is not so important.
The IC-706Mk2G turned out to be very easy to fit a phono connector on the back panel of for the IF output. On the back panel is a small shiny blanking plate, which is easily removed with 2 screws, under which is an 8mm hole ideal for a phono connector, or SMA connector if required. This means no drilling was required.
The phono connector is seen fitted in the middle of the rear panel with the shiny plate on the desk. On the inside I tightened the phono mounting bolt and put some ‘screwlock’ on it to stop it coming loose at any point.
Another length of RG-178 was connected between the output of the PAT board and the phono connector the back panel, to do this the filter board needs to be removed to route the RG-178 under to make it all fit, this does require the bottom panel of the radio to be removed so that an RF cable connected between the filter and PA boards can be undone which is required to allow the filter board to be lifted sufficiently to be able to run the RG-178 under it.
DC Power to PAT Board
The PAT board requires 5v to 12v DC varying between 5mA and 10mA current draw respectfully. The IC-706Mk2G has very accessible 8v and GND (0v) points over C647 which is located next to the optional filters.
It might be useful to use the R8V line to power the PAT board when mounted in the IC-706Mk2G radio, the R8V line is “8v on RX” – this would mean that the PAT board only has power when in RX, C647 is a permanent 8v.
SDR Output – HDSDR
This is how the IC-706Mk2G IF output, using the PAT interface, looks like in HDSDR. Note the shape of the signal in the waterfall, the peak in the middle is down to the 1st IF filter bandwidth but signals +-60KHz are easily seen.