Marconi Basic-7 Marconi Basic-7 is a 7MHz QRP CW Transceiver kit.

The first time I read about the Marconi Basic-7 was at the presentationGeorge G3RJV made in the winter edition of the QRP magazine SPRAT.Thereafter things got the way of e-mail communication and after I checkedwith myself where I would be next month, I orderd it. The designer is anexcellent Japanese gentleman called Hidefumi Seike, Hidy to his friends andwhen you know him well!

It comes with a pre-drilled box with dimensions H x W x D, 7 cm x 16 cm x16 cm x 18 cm and weighing 1.3kg. With anti slip rubber feet the totalheight is 8 cm. Photo 1

It comes supplied with a 20 page manual with diagrams and detaileddrawings for the hardware assembly and assembly of the kit itself. Photo 2

The package except for the necessary components includes accessories likecables to connect the board with potentiometers, switches and connectors.Photos3,4

There are included also components for the construction of an RF probe forthe necessary measurements during the alignment!

The components bag even contains a 51 ohm 1W resistor to be used as aDummy Load!

Features:

Output Power: 1.5W VXO 7.020 ~ 7.040 MHz Direct Conversion receiver RF att potentiometer at the antenna inputRIT Full break-in Sidetone Power requirement 12 VDC 250mA

A starting price set by the manufacturer is 100 USD, which of course sounds a bit expensive, but the final price is being underthought and negotiation, I understand. In a later e-mail, Hidy told me that he intends to have the kit without box.

This kit is his spiritual child, because from cradle to grave is the product of the his skills and knowledge! The stages of thistransceiver are derived from projects that describe each one separately.

The Direct Conversion receiver with the use of a very good oscillator is very stable and sensitive but is prone to large signals atits input. There can be no Automatic Gain Control (AGC) and that justifies the existence of a potentiometer at the antenna. The crystal oscillator, by adding a variable capacitor, becomes variable within a tight range and after a buffer stage, it drives thetransistor output. The T/R switch is a single transistor with very fast timing and the RIT tuning isachieved by applying varying voltage to a varicap. In a new e-mail from Hidy, Iwas informed of the addition of an LED as a visual tuning indicator, and also asan indication of output power!

After I lined up the components before me, I stuck them in a piece ofStyrofoam to have them at hand during construction. Photo 5

Hidy urges us to mount the potentiometers and other miscellaneous parts in the case. Note theholes for the lugs in photo 1 to stop the pot from turning.Unscrew the board to begin construction by placing the terminal pins. It is a little bit difficult to pressthem in and it is good to mind your fingertips! (Perhaps a pair of long-nosed pliers would help .. Ed.)Solder them to the board as a next step place the RF coils on the board. Photo 6, 7 & 8

Except for T1 and T7 which are different, the coils T2, T3, T4, T5 and T6 are the same. Duringsoldering do not bend the two legs of the coil case because if a mistake happens and you want toremove them, it would destroy the coil.

The first circuit in the assembly is the VXO oscillator. Take care as always not to over-heat thecomponents and with the placement of transistors. Take care, the single RF Coil looks like a bigresistor, but with color dots and not bands.

The next circuit is dependent on the oscillator, and it is the RIT. Pay attention to polarity of theVaricap when installing it! It is drawn on the schematic clearly by Hidy but still make a second check!

The buffer stage is next, with two parallel FET transistors (2SK241) in Darlington configuration.

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It is time to start doing the ferrite coils now. Maybe you don’t like it but I will try to guide you andencourage you all the way!

The wire contained in the materials bag is enough for 10 small turns in the L1 ferrite. Pass the wirethrough the ferrite, leave 5 cm wire and start winding! The first pass of the wire though the ferritecounts as the first turn. Another 9 and you're done!

It is harder to handle the ferrite than the winding itself! Tighten each turn and don't spread themevenly; you do that at the end and thus tighten them more! Photo 9

I have done my best taking the photos so to help you get an idea of the progress of construction.

Construction continues with the low-pass filter output. Solder the four 470 pF capacitors to getcourage. Carefully unfold the 0.4mm wire in order not to make kinks. The three pieces of wire thatyou will use are included in the kit miscellaneous bag and are carefully folded!

Pass 5 cm wire through the ferrite and start winding. Wrap the turns tightly side by side, being carefulnot to overlap the turns, into the hole where it is most evident. Spacing the turns at the end willtighten them further.

Every time the wire passes through the center of the ferrite it counts as a turn. If you countthem at the end they will be 18 plus one because of the wire passing through the centre. Photo10

Trust me, it is not difficult. I had more difficulty holding the tiny ferrite between my fingers,rather than the winding itself! Photo 11 shows the coils mounted on the board.

You finished with the transmitter and now you will start the receiver in accordance with thedesigner's instructions.

Resistors and capacitors this time only! Pay attention to C32, which is multilayer and not ceramic.It is one of the two tiny blue capacitors which are hard to read the value on their backs!

Take care also to the installation of two germanium diodes. The black lines on the glass show thecathode. Photo 12

There is a minor modification, which you should make to the PCB circuit, at the legs of LM 386(circled in photo 13). If you go back to look at the schematic of the project you will see that pinNr3 is grounded and pin Nr2 receives the audio frequency (AF) from the mixer and the soundside. You should carefully cut the PCB around the pin Nr3 and track at the PCB board just below3. It's the track that comes from the VR 2 and with the help of a small wire you will connect it topin Nr3. Photo 14

I think future kits will be corrected and you will not need to intervene. Nevertheless, click on theimage of the board and zoom in until you see it well!

Fortunately there is nothing else to worry about other than the capacitor C35 that is the secondmultilayer you have in your bag and also two small germanium diodes.

Last parts to complete the construction! The side tone circuit has four resistors, four capacitorsand one transistor with a small onboard potentiometer to adjust the volume. Last circuit is theT/R switch. Be careful as always, in polarity of the germanium diodes.

Congratulations! You finished with the construction and this is whatthe final product looks like.

73, Peter M/SV3AUW

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