mcHF V06 TX-RX relay antenna switching as implemented by Wolfram PY2BND

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When I had to make the modification of my mcHF V06, due to the breakage of a pin diode in the antenna switching circuit, I forgot to document with photographs -step by step- the modifications that had to be made on the RF board. At the time I thought my explanations were enough. Although I was able to personally comment with Chris M0NKA on the modification I had to make as I did not have a replacement for the PIN diode quickly, I had no response from any other radio amateurs who would have carried out the modification.

Until Wolfram Perrey, PY2BND, contacted me from Brazil asking for details of the implementation. In his case he wanted to carry it out to improve the transmission signal. Before continuing, I must add that Wolfram is a very qualified engineer who would not have needed my additional explanations to carry out the modification, but Wolfram had the idea of doing what I did not do: doc…

My third mcHF will no longer be QRP

A 120 watt mcHF variant is born. Even so, its size will be small compared to the much more expensive. Stay tuned

Inside a Retex SOLBOX there is still room for a 120 Watt linear amplifier, four 7-pole low-pass Chebysehv filters, forced ventilation ... and even a 12-volt 20-amp switching power supply, but only if I can shield it for avoid interference from 40 kHz. In any case, a conventional 12-volt 2-amp source would facilitate QRP operation. A dial for CNC tool, instead of a simple button, I hope it gives a touch of distinction. 
Entertainment for my summer vacations.

mcHF TCXO error: MCP9801 not present

Since December 2018 the MCP9801 chip is an option in the mcHF. However, the printed circuit is still routed, only missing the component MCP9801 that is not mounted in factory.

If you want to avoid the delay at startup with the M0NKA software or the "SENSOR!" error message on the display with the USHDR Software, soldering the MCP9801 chip is easy

The TCXO field value show an abnormally high temperature because MCP9801 has just been soldered to the printed circuit and remains hot.

The MCP9801-M chip in SOP-8 format can be purchased for € 0.72 on Aliexpress.

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 first separate the supports of the transformers T1 and T2 (cut them from the printed circuit) and then solder the components of small size. Leave the fan and PTT connector for the end. These connectors prevent solder 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 the half turn of the primary. Use a 100 Watt flat tipped soldering iron to build T1 and T2 and solde their brackets to the printed circuit board. Contrary to what i…

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

See also related post. mcHF V06 TX-RX relay antenna switching as implemented by Wolfram PY2BND

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.Unlike df8oe, I used an NPN transistor to pilot the relay. Now switching transition between RX and TX is done the way that the RX band-pass is completely disconnected and grounded before …