MiniPA-70 and MINIPA-100 step by step

The difference between transmitting with 5 or 12 watts of power in practice will not reach half a unit "s" in a remote receiver, however, that can be the difference in critical conditions to achieve a QSO. But the mcHF behaves much better emitting with its nominal power of 5 Watts, that's why a "help" in the form of linear amplifier is a better option when necessary. MINIPA-70 or MINIPA100 is a good  and unexpensive "help".

My recommendation is to first separate the supports of the transformers T1 and T2 (cut them from the printed circuit) and then weld the components of small size. Leave the fan and PTT connectors for the end. These connectors prevent the welding of other nearby components and can easily melt due to excess heat.

In this way the transformer T2 is built. The two small metal tubes are actually the half turn of the primary. Use a large 100 Watt flat tipped soldering iron to build T1 and T2 and to weld their brackets to the printed circui…

Improvised dummy load.

I had to adjust the PA of my mcHF and did not have a phantom charge at hand. I looked in "the trunk of the junk memories" and found an old instrument of 50 μA DC full scale that was never used. I only had to buy 29 carbon resistors of 1,500 Ω, 2 Watts, which were connected in parallel to obtain a value of 51.72 Ω. Everything was put in an ad hoc box. A PL259 female connector was located on the rear and another female BNC connector on the front. The idea was to obtain in the BNC connector a sample of the attenuated input signal ten or one hundred times, to analyze it in an oscilloscope.

Since the original idea was to use it up to 30 Mhz, no precautions were taken to arrange the resistances around a radial conductor, it was enough to connect them in parallel as close together as possible and keep short terminals. With copper ribbon, all terminals were joined on each side. The signal present in the load resistor is rectified with a diode bridge 1N4148, then filtered with a 100 …

A cheap extension connector for mcHF V06

With a pair of 2.54 mm in-line male/female connectors and a piece of printed circuit board for prototypes, you can easily made an extension for mcHF V06 boards.

I used a 40-pin connector and carefully cut the remaining 10 pins. In this way you can have an mcHF running at the same time that you can access both sides of each board.
To avoid accidents, when mounting the mcHF, the female connector must be installed on the mchf_rf board. The reason is that this board supplies the supply voltages to the mchf_ui board. A male connector with power supply pins is always a potential risk.


It is possible to take +8 V (track 28), +5 V (track 27) and +3.3 V (track 26) in the connector/extension, as well as the connections to ground to use measuring instruments. You can also proceed in reverse way and apply power to mcHF_ui board by injecting the +5 volts into pin 28 of the connector, in this way you can update the firmware ( I use the bootloader 4.0 of df8oe) without having to connect the mc…

mcHF V06 TX-RX antenna switching: Pin diodes vs Relay

This is the modification that I just made in my mcHF V06, inspired in df8oe RF-04/05/06-H-029  upgrade. In my case, I had to make the modification due to failure of pin diode D3.

Clic here to see the df8oe modification
Click here to see "The pin diode circuit designer' Handbook"
The variant has been to connect a G6S-2 signal relay as a switch of the antenna signal, but taking care that capacitor C81 is earthed in TX mode. Else, in RX mode, the antenna is isolated from PA out. In this way, the shunt function of D4 pin diode is emulated. Protection by diodes 1N4148 -or similar- has always been discussed because the intermodulation effect that would cause an incoming strong signal exceeding 500 mV.

I have not been able to check if the sensitivity of the receiver increase, as indicates Andreas, df8oe, since I do not have another pin diode MA4P7102F in good condition to do the check. In any way, in the original versión, when RX mode, the incoming signal has to cross diodes D3

Modification in mcHF V06 to make accessible the jumper P6 on UI-board

The P6 jumper, located near the MCU, allows you to write the bootloader for the first time (in a new MCU) or also to replace the bootloader when necessary. The problem is that jumper P6 is located on the inside face of the UI board. It is highly recommended to "extend" the jumper towards the edge of the UI board. In this case, I stuck a waste of a female connector with glue and made the male jumper by joining two pins of a male connector.

In this way you can rewrite the bootloader without having to disarm almost completely the transceiver.