by Jim Pollock, KW2R

[Editor's note: You can view the document (below) or download the original Word v6 document to your system.]

Introduction

We had a lot for fun putting this little rig together! It is a very forgiving design that invites experimentation. If ever there was a project that could be recommended as a club activity, this is it!!! This design has the potential to proliferate by the hundreds across the country .

The assembly notes for this project offer a perspective on the transceiver’s flexibility of design and functionality. The notes were written to provide continuity for repairs and/or changes to address the 20, 40, and 80 meter bands in future projects.

The band of choice for this rig was the 30 meter Band; 10.100 - 10.150 kHz. There were changes made to the NN1G VFO design to allow for complete band coverage.

Our notes offer parts lists, construction hints, and assembly aid sketches.

One of the surprise features is that the rig has sidetone!! The carrier mixer oscillator of the transmitter and the product detector oscillator of the receiver beat against one another to produce a nice beat note in the headset when the transmitter is keyed!! Sidetone frequency can be adjusted by changing capacitor C16 at the product detector. The amplitude of the sidetone can be increased by decreasing the 4.7MW resistor next to FET transistor Q1.

Jim Pollock, KW2R
216 Kingsley Court
Mount Laurel, New Jersey 08054
kw2r@juno.com (qth)
pollo@erinc.com (salt mine)

Joe Silvasi, KC2J
12 North Pemberton Road
Pemberton, New Jersey 08068
jsilvasi@db2-idms.com

Test Equipment List.

Use this probe for DC voltages under 25 volts; RF voltages under 25 volts P-P.

Use with a VOM with a high impedance FET input. Connect the ground lead as close as possible to the ground of the circuit under test.

Parts List for the NN1G CW XCVR

30 Meter Version Components

 = See Components substitution chart on the next page.

‚ = Quantity adjusted. Quantity understated in the original parts list.

ƒ = Ten turn potentiometer for the main tuning.

„ = Quantity adjustment due to the process of component substitution.

Component Substitutions

The impetus to become creative with this project was driven by several factors:

1. Stock of resistors, capacitors, quartz crystals, and ferrite materials on hand at KW2R and KC2J.
2. The desire to cover the entire 30 meter band; including ¼ Kilowatt Alley.

NOTES and HINTS

Assembly Sequence

Assemble the PC board by installing the passive components first: the active components last.

Passive Components

• Resistors.
• Capacitors. (fixed and variable)
• Transformers and Inductors.
• Diodes, (Zener, Varactor, and Small Signal Diodes.
• Quartz Crystals.

Installation of all passive components will allow you the clean up the work area, and also keep better track of the few remaining active parts to be installed later.

Active Components

VFO

• Q2

Receiver Section

• U1,U3,Q1,U4

Transmitter

• U5,Q3,Q4,Q5,Q6

Save Q6 as the very last part to be installed on the board. The driver transistor Q5 is already terminated with 100W . Once you have the rest of the rig working and have verified that there is drive from Q5, it is safe to install Q6 for dummy load testing.

VFO Alignment

The best place to start with this project is with the VFO, since it is common to transmitter and receiver operation.

The VFO was tested with the original component values given by NN1G. The approximate frequency recorded on a frequency counter at pin 2 of U5 was in the neighborhood of 2.1 mHz.

The receiver mixer injection point (U5 pin 2 ) was used for tuning range measurements because the test probe of the frequency counter approximates the loading factor presented by U5.

The original tuning range of the VFO as designed by NN1G was very interesting.

The tuning range was barely 20 kHz. Perhaps NN1G had intended operation within a small band segment that included the QRP calling frequency. The QST article mentions that one of the operating techniques is to stay away from "Kiliwatt Alley". However, on 30 meters, the maximum power is 250 watts.

Also, the frequency of the VFO was too high for the 8.192 mHz IF chosen for this project. NN1G had designed the project for an IF frequency of 8.000 mHz. Thus, the VFO had to be shifted down about 200 kHz to make "the numbers" come out correctly.

Redesigning the VFO

VFO Frequency Range.

To make the project operate within the 30 meter band, the VFO tuning range had to include frequencies from 1.908 kHz through 1.958 mHz.

The alignment of the VFO can be checked on a receiver that is capable of covering the 160 meter amateur band.

The VFO is quite stable. The high "C" to "L" ratio, and its relatively low frequency of operation contribute to its stability. The relative large values of net capacitance of the VFO tank circuit make it less sensitive to proximity effects. Of course, when the completed project is housed in a metal enclosure, stray capacitance is a moot point.

Dope your coils with polyurethane (fingernail polish) and glue ‘em down to prevent vibration induced frequency modulation!

Changes to the VFO Parts List

The follwing table is a list of athe component changes that were made to adapt the VFO to the new IF frequency of 8.192 mHz.

Tuning Range Factors.

One of the limiting factors was the D C tuning range of the varactor diode when compared to the baseline capacitance contributed by C5 and C8. The series equivalent capacitance of C5 and C8 had to be lowered in order to make the varactor more effective.

Tuning range is also dependent on the RF sinewave applied to the varactor.

Maximum tuning range is obtained when the bias voltage adjustment range is large when compared to the peak-to-peak amlitude of the RF sinewave that is applied to the varactor.

This is one of the critical factors in varactor tuned oscillator design. In circuits where the tank circuit handles a large RF sinewave, the sinewave modulates the varactor, and thus limits the effects of the tuning control voltage.

VFO Alignment Hints

. Proper operation can be checked with another receiver, or a frequency counter.

• Begin receiver construction by installing the transistor and associated circuitry for the VFO. This includes the voltage regulator.
• Once the VFO is confirmed as in working order, install the NE602’s and the Dual Op-amp to complete the receiver.
• Check the receiver for proper operation and tuning range. When the receiver is working, it will make the assembly and check out of the transmitter much easier.Receiver construction should begin with the VFO. The VFO is common to the receiver and the transmitter. VFO operation can be verified with another receiver that is capable of tuning the 1.8 to 4 mHz range. The target frequency range for the VFO is 1.75 to 1.9 mHz.
• Install the Tuning and RF Gain pots to check receiver operation with an antenna.

Typical MV1662 Varactor Diode Characteristics.

The test conditions for the following measurements:

• Test instrument: A.A.D.E. L/C meter II
• Test sinewave voltage = 0.5 volts P-P.
• Feed bias resistor = 1 Meg-ohm.
• Bias-to-L/C meter blocking capacitor=0.01 uf Polyester Film.
• V_T = Varactor Tuning Voltage.

VFO Range after Modification

The wider adjustment range of C8 results in a shift range of +/- 15 kHz.

Construction Notes

Printed Circuit Board

The Board does not have a silk screen overlay that marks location and orientation of the components. You will have to refer to the components placement drawing and the schematic to sort things out.

Diodes

Diodes are mounted as a radial lead components, with the cathode facing away from the board. All of the diodes, with the exception of the 1n5256 Zener, are mounted into the PC board by using the hairpin bend on the cathode lead.

6mm Trimmer Capacitors

The trimmer capacitors, C23 and C26, should be mounted with attention given to grounding the rotor plates. The outer shell and the rotor plates form a shield that prevents detuning due to proximity effects.

NE602-NE612 Operating Voltages

DC operating voltages on all pins of the NE602-NE612 Osc-Mixer chips were measured with a Radio Shack #22-216 analog FET VOM.

Measurements were made at U1 and U3 after the receiver was aligned and working.

Transformers

Transformer T2.

This transformer was made by winding 5 turns onto a #43 ferrite FB43-2401 Ferrite Bead Core. Wires with insulation of two different colors were used to make identification of the windings possible.

The windings are connected in series to form a 2:1 step-down auto transformer.

The site location on the PC board can be a little confusing.

Our suppliers:

• Dan’s Small Parts and Kits
• http//www.fix.net./dans.html (very nice internet catalog)
• Box 3634
• Missoula, Montana 59806-3634
• (Matched sets of Crystals, Transistors, Ferrite cores, trimmer caps, NE602,NE612 chips Ferrtie and Iron Powder Cores)

• Digi-Key
• 701 Brooks Avenue South
• Thief River Falls, Minnesota 56701-0677
• (Polyester and polypropolyene film capacitors, COG ceramic Capacitors,)
• (Sprague-Goodman trim caps., Trim pots.,)

• Hosfelt Electronics
• 2700 Sunset Blvd
• Steubenville, Ohio 43952-1158
• (10 Turn Pot., RF Gain Pot., Silver Mica caps, 6mm Trimmer caps, 12 volt wall warts,)
• (Zener diodes, MV1662 Varactors)

• FAR Circuits
• 18 N 640 Field Court
• Dundee, Illinois 60118
• (Printed Circuit Board, $6.00 each plus $1.50 for shipping for up to four boards Assembly and parts layout diagram included!!!).

• Amidon Asociates
• P.O. Box 25867
• Santa Ana, California 92799.
• (Ferrite Cores)

• Small Wonder Labs
• 80 East Robbins Ave
• Newington, Ct 06111
• (Board, and all on-board parts, $50.00 ppd)