Miscellaneous Pictures and Schematics

This web page is for pictures and schematics which may be of interest, but did not make it onto the main topic pages. Some have nothing to do with amateur radio. Others may be boring or silly.

73 de VE7BPO!



Mouse over the images on the left to view full size version.



The Electroluminescent Receiver of David White, WN5Y looks gorgeous in a transparent Plexiglas case. A link to David's web site may be found on the Site Info and Links web page.

A product detector much improved by W7ZOI that I fed with a center tapped output coil on the VFO amplifier. My original design had serious biasing problems which Wes resolved.

A pair of trifilar inductors used in the tuned circuit of an RF amp. I had trouble with spurious oscillations unless a shunt resistor was placed across the coil.

Details of a JFET biasing experiment suggested by W7ZOI. For me experimentation has greatly improved my knowledge and project quality.

In EMRFD, Wes has a cool receiver called the SC7 which has feedback IF amps that use a -6dB pad as the collector resistance to help set the input Z and define the output impedance. They use no inductors. I wanted one for 225 ohms Zin/out and W7ZOI helped me with the design. The FBA program is from EMRFD. The programs on the CD that comes with this book are very helpful for the experimenter. An experiment with the IF amp is shown in the third picture. Further experimentation is warranted with this concept.

In EMRFD, Wes has a cool receiver called the SC7 which has feedback IF amps that use a -6dB pad as the collector resistance to help set the input Z and define the output impedance. They use no inductors. I wanted one for 225 ohms Zin/out and W7ZOI helped me with the design. The FBA program is from EMRFD. The programs on the CD that comes with this book are very helpful for the experimenter. An experiment with the IF amp is shown in the third picture. Further experimentation is warranted with this concept.

In EMRFD, Wes has a cool receiver called the SC7 which has feedback IF amps that use a -6dB pad as the collector resistance to help set the input Z and define the output impedance. They use no inductors. I wanted one for 225 ohms Zin/out and W7ZOI helped me with the design. The FBA program is from EMRFD. The programs on the CD that comes with this book are very helpful for the experimenter. An experiment with the IF amp is shown in the third picture. Further experimentation is warranted with this concept.

A VPA on the bench after measuring the DC voltages with a homebrew high impedance volt meter.

Scope adventures at VE7BPO. This is a 12 MHz BFO output.

Our kitty. She is the background model in the filter sweep graph on the tuned Q2 input VPA page. She sleeps 16 hours per day and eats like a horse.

My thirsty cat. Why do they so love toilet water?

An 80 meter version of Rick Campbell, KK7B's R2 direct conversion receiver. This rig sounds fabulous. On the top left is the VFO compartment. The right sided chassis (minus screws) is a special preamp that connects and amplifies a 75 ohm coaxial snake antenna that is placed on the ground.

One of the 2 commercial kits I have built. This is the 30 meter kit version of the W7EL Optimized Transceiver sold by Oak Hills Research in the mid 90s. This kit design added a bandpass filter before the diode ring product detector which helped a lot. I have built an ugly version of Roy's famous receiver as well, except I used a lowpass audio filter instead of the bandpass filter of the original design.

Three views of an old TTL keyer I built which drove a reed relay, I originally built it for my Drake Twins but also used it for an Icom and various home built QRP transmitters.

Light Emitting Diode Flasher

An astable multivibrator is used to alternately flash 2 LEDs. Collector resistors are used in series with the LEDs to limit the current to ~ 20 mA. Read the web page on Astable Multivibrators on this site for information on how to set the flashing frequency to a desired value. The emitter diodes maybe omitted if you like. Simply connect the emitters directly to ground. The diodes prevent emitter-base breakdown.





Popcorn IF Amplifier

This low cost IF amp stage was developed by Wes Hayward, W7ZOI and is used by permission. It is a common-emitter feedback amp biased for around 5 mA IC and is suitable for low-cost popcorn receivers as an IF amplifier following a crystal filter. It can also be used as a temporary IF amp in a receiver you are developing. Q1 is a 2N3904 and T1 is 10 bifilar turns of # 28 AWG enamel covered wire on a ferrite FT37-43 toroid. Input and output impedance is ~50 ohms. Noise Figure is 5 - 6 dB. IP3 Out is ~ 15 dBm. Stand more current if you require better IMD Shunt feedback and a broadband ferrite transformer at the collector provide good stability. At 10 MHz, the stage can have up to 18 dB gain which falls to around 14 dB at 40 MHz. Use hotter transistors such as the 2N5109 at higher frequencies. It is important to feed and terminate this amplifier with a 50 ohm impedance as each can effect the other. Several stages can be cascaded for practical use in a receiver.

VE7GC Continuity Tester


Here is another fun schematic from Dick Pattinson, VE7GC. This audio frequency oscillator is used as a continuity tester. The current drain using a 1.5 v. cell is 4 ma when probes are shorted. At that time the current through them is 0.005 milliamperes which should not hurt any circuit! With the probes not shorted the drain on the cell is zero. The D cell in the circuit will last many years and in Dick's version, is a D cell that is over 20 years old. The 50K trim pot is used as a tone control and may be replaced with a 47K fixed resistor. The choice of transistors for Q1 and Q2 would be almost any bench-sweepings transistors you have around. A continuity tester is a great first test-equipment project for your electronics work bench.


75 Meter Band Marine Tuner



Here is a 75 M tuner schematic from VE7GC. Dick uses this aboard his fiberglass sailboat Gwaihir. It is for useage on a vessel with ungrounded rigging. This allows the rigging to be loaded up for an easy antenna. Signal reports with the rigging were better than a scientifically designed antenna for 75 Meters so Dick stuck with the rigging antenna. The coax from the transceiver has the braid going to ground via the Keel bolt. The center conductor connects to the tuner as shown. A 12 position switch is used to vary the L2 inductance, although only a 6 position switch is shown in the schematic for brevity. The L2 inductor is an air wound coil consisting of 26 turns of wire with a total length of 1 and 1/16th inches. The coil diameter is 1.5 inches. Dick actually used is Airdux 10273A and tapped every other loop starting at #3 from the input. I have wound similar coils using #20 AWG wire on a wooden dowel form of the the correct diameter.

The L1 coil is simply two turns of fine wire around a cylindrical ferrite bead such as a FB-43-2401. The antenna wire passes through the center of the ferrite bead. This is then rectified and powers a salvaged tape recorder meter for a relative RF power meter. I have seen Dick use a similar technique in his QRP transmitters , where he connected the L1 wires directly to an LED for a transmitting monitor

Coilguy