Created on December 31, 2012 7:06 PM Local time Australia.

Last updated on December 31, 2012 info on PA/LPF connections and also LED's in Matrix added

QC tab and tinplate info added

These notes are to clarify some areas of the PCB assembly.

If there is anything you are unsure of, email me and I will add to or modify this page.


DC input supply

The DC input is via two 6.3mm Quick Connect (QC) tabs. (eg Farnell 4215618 perhaps) The mating part is commonly found in automotive stores and it is suggested that two be used to reduce voltage drop. The tabs may be mounted on the top or the bottom of the PCB; to suit whatever DC input connector you elect to use. { consider how you will fit the input connector and PA's when deciding on which side to fit the quick connects} A relay is used to provide reverse polarity protection. The relay used need only be a DPST type but the PCB will also take DPDT types. I used a similar relay to that used on Picatune. Most relays of this type will be rated at about 10-16amps per contact and the contacts are paralleled. Since the relay is not hot switching the PA DC supply, it should be able to carry the supply to the 140w PA also. Again, the output quick connects may be mounted on either side of the PCB, as may the relay. There is provision on the PCB tracks to solder a wire to beef up the track also. Check your relay is not polarized though. ie voltage applied to the coil either way round, should operate the relay.

The "power on switch" is tracked to the very front of the PCB at the left side, adjacent to 5 volt regulator, IC303. If you don't want to use a front panel on/off switch, simply bridge this connection. The pins are also available at the rear, near the relay, for a rear mounted switch.

NOTE: For most builds using Trxavrb, regulator IC303 is not used so need not be fitted.

< added 15th Jan, 2009 > There is also provision for a fan connection with a series resistor to set the 'speed' if required. Adjacent to the relay also. The resistor is fed from the 12v supply and terminates with 2 holes for the fan. This is shown on the schematics. Value to suit relay used (12v) NOTE: Fans may cause interference to the receiver or transmitter and may require filtering.

Line output transformer.

This is totally optional; to provide a balanced (mono) line output and in truth, rarely needed. You need to select the resistors R912A or R913A to fit to provide either Right or Left output or fit both as a crude mixer of both Left/Right signals. The value shown is nominal. You may need to alter it. There is a trim pot to set the level. This is obviously also dependant on the normal audio level setting. The transformer I used is a 1:1 audio type, commonly available in Australia but an exact equivalent may be difficult to find.

For a simple unbalanced output to feed, say, the PC sound card, simply fit R912, R913 and the "ground" return, R950 (0R). The value for R912/913 is not shown but 100R is suggested as a starting point. The transformer is not required.

Opto Isolators

Caution, one device is fitted on the BOTTOM of the PCB.

Alternate Parts

Note, in some areas there are dual footprints for parts to allow the use of alternate types. This also applies to some of the regulators so that LM317's can be used instead of harder to get parts. See the IF area and also the DSP/Codec area's. Both parts will be shown on the BOM. One will be shown with an "A" or "Alt" (alternate) suffix.


The PCB has clear resist areas around the various blocks of the radio, to fit shields. It is best NOT to fit the shielding intially as the radio will function without them and you may need to work on the PCB for some reason. When you are happy after testing the radio for operation, the shields can then be fitted. I used 0.4mm tin-plate (#682-450 from RS-Components) in my original build but the clear areas should also allow PCB material to be cut and soldered down. Whatever you use, the walls must be cut to clear all of the components fitted to the PCB. { RS also list 0.5, 0.6 and 1mm but as "call RS". On the RS-C web pages, search for "tinplate" }

NOTE: there are some areas where the bottom edge of the shield partition must be slightly filed to ensure that tracks passing underneath will not be compromised (ie shorted) This will be obvious on inspection. I suggest that you only tack solder the shields in place initially.

On the bottom of the PCB, the same areas have been cleared of resist also. Again, you need to shield these areas also although the overall height of the shielding will be very low. It may be simpler to use tin-plate on the bottom, formed into a cover with its own edges. Tin-plate from large coffee cans etc could be pressed into use for this. I suggest that a coat of protective PCB lacquer be sprayed over tinplate as it has a tendency to rust eventually. (Unless tin-plated brass can be found) Indeed, brass or copper sheet could also be used. One way to form a cover is to use hi density wood like "MDF" cut to size. Trim the tim-plate to size, including the folds (with the corners cut out) then clamp the tin-plate over the MDF former and fold the edges over using a piece of wood or a rubber mallet.

Shielded Wiring

The shielded wires carrying RF signals, indicated under the PCB should be good quality RG174 or similar. Other wires use audio shielded cables.

Be careful when soldering the top co-ax cable shield to GND from "xfmr601" as the 10v track adjacent, has no resist over it.

Internal Speakers

There is provision on the PCB (as marked underneath) to fit internal speakers in your PICaSTAR build if you have the room in the case. Plugging in external speakers to the rear 3.5mm jack will switch off the internal speakers.


The microphone and PTT line should be wired from your chosen Mic. Socket to the points marked on the bottom of the PCB. Note the PTT wire is some distance from the Mic. Input. Shielded wire should be used for the Mic. It may be prudent to also fit a ferrite bead over the wire also.

CW key

A rear 3.5mm socket allows a straight key or other, to be plugged in at the rear. These points are also available under the PCB for direct wiring elsewhere, if the rear socket is not to be used.

DDS Control

I have had no difficulty with the DDS control lines in the 20-way ribbon cable, controlling the DDS. There is also provision though for a 4-pin connector "J4_PnM" to be used to wire the DDS to the controller. If you elect to use this connector, remove resistors R1, R2 & R3 under the DDS area to isolate the control lines form the IDC cable.

Opto Tuning encoder.

I suggest you wire your encoder directly to the Trxavrb PCB and not use the connector "J304" on the left side of the PCB. J304 is connected through the IDC cable.

Low Pass Filter wiring

The low pass filter is connected using a 10 way IDC cable to the PCB. At the LPF itself, the cable must be separated and connected as required. The pin out of the IDC connector is shown on the PCB.

PA control (PA Bias) < this section was changed on 29th Dec, 2009 >

"PA Control" from the Timer, connects via a PCB track to J701 on the Diode Matrix LPF connector. A 10 way ribbon cable from the Matrix then connects to the Low Pass Filter per the designations shown on the PCB and schematic. eg 12v, Atten. and the various LPF band selects. The PA Control runs to the 20W and 140W PA's. For preference, all wires into the (shielded) LPF section should run via feedthrough capacitors.

PA (T/R relay changeover) < this section added on 29th Dec 2009 >

"PA" must be connected from the Timer, J702, pin 2 to the LPF "T/R" switch pin. The wire can pass through the adjacent hole in the PCB, to the LPF board.

LED's in the matrix area: < added 31-12-09 >

Not a problem in the PCB but might catch you out:

The wide band LED mounts on the pcb the reverse direction of all of the other band LED's - Caught me out - might catch others. (Thanks Paul Craven)



Fit a small heatsink or scrap of aluminium to the 5volt regulator adjacent to the Butler oscillator. Ensure you leave plenty of clearance to the Butler enclosure to avoid any heat transfer.

Trxavrb PCB

This PCB is the 'controller' to replace PICnMIX. It is slightly different to that supplied in the previous TrxAVRB interface panel. Due to lack of space, the additional connectors for the various optional display types are not provided. If you have already built the interface panel version, it may be used also. On the PCB supplied with this panel, only one connector, 20-way IDC "J6" is fitted. I will provide more info on using this connector later as I get time to do the drawings. In the meantime you can refer to the Trxavrb schematics.

No PCB is provided for any keypads either, but a standard 4x4 keypad can be used for the main keypad. Other keys and encoders are optional and need to be directly wired by the builder.

If you are only going to fit a colour display, then connector "Jx1" will be used for that. At the moment, only the "Electronics Assembly" display can be used, until the TFT group complete the required additional TFT PCB needed for the low cost version. This is progressing very well with several prototype PCB's working. Some changes need to be made to the TFT PCB to suit parts available etc.


I have some drawings to make a suitable case if you have reasonable facilities. I have made one myself following this information and so far it seems to be working out nicely. You do need bending facilities though but a fabricated version using flat sheet and right angle extrusions could also be made. Indeed, PCB material could also be used as the Combo PCB has provision to solder around the edges in most places.

I did submit the drawings to a local sheet metal vendor and estimated cost was about AU$95 with top and bottom covers powder coated for 10 pieces. (no postage included !) Front and rear panels unpunched and not finished as it would be difficult to accomodate all the variations available for displays etc.

If there is interest, I will post the drawings also.

In my own build, I have now decided to use an old instrument case similar to the one I built my original STAR in. To make a matching pair so to speak. Combo PCB will be mounted underneath, and the PA's and LPF on top. I will post a few pictures of progress later.< see builders pages >


DSP Loading

For the initial loading of the DSP, place the rear mounted switch in the left position when viewed from the front of the PCB. Follow the official documents on the "picaproject" Yahoo site.

The switch used is a PCB mount horizontal action type. NOT the usual up/down style.

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Combo AA (proto "Combo")





last updated on December 31, 2012
Created 14th Dec, 2009