Odds and Ends

A Random Selection of Various Projects, Modifications and Experiments

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Tuna Tin II One of my first QRP kits. This one’s built in a pineapple tin.

Also built the TTII circuit manhattan style and added a keyer circuit and a simple VXO. The circuits found in the W1FB QRP books from ARRL.

The Tuna Tin II is presently being sold by the LobsterCon folks via Rex Harper, QRPme.com, to support their hamfest efforts.
Tuna Tin II

MRX-30 An Altoids tin is used as the enclosure for this neat little radio. The circuit is a modified version of that used for the original MRX-40. The schematic for this receiver is shown below. MRX-30 Receiver
MRX-30 Inside The PCB for this project was obtained from Far Circuits. Makes a neat little package to carry in a pocket


External 9V Mod
Built this excellent meter from a kit. A 9V battery is the supplied power source. My inclination to leave it turned on after use depleted too many batteries. So I added a 9 Volt regulator circuit and external power jack. Worked out fine. For portable operation away from the shack, I can still use the 9 V battery. A description of the installation was included in the ARCI QRP Quarterly. LCIIB 9V Regulator

25 Watt Dummy Load This dummy load is built in an Eagle cast aluminum enclosure.

A PCB was cut-to-fit and used to mount the resistance element.

An Ohmite thick film resistor (Nom 51 Ohm) with ceramic substrate is used for the resistor. (Ohmite TA025W51R0J)
K12 Front
K12 Back

K12 Inside

Using equipment at W5YR's shack, the dummy load checked out quite flat for frequency response from 1.8 to 60 MHz. The resistance varied from 48 to 52 Ohms. Stray capacitance and inductance were negligible. Using my MFJ-259B, it looked good to about 175 MHz. Since this picture was taken, a 1N34 diode and .01 pF filter cap was added at the BNC connector.

RF Probes Probes for 3 different meter input Z, 10 and 1 meg for DVMs and for a VOM with a 12 VFS DC scale (Triplett). Diodes are 1N34a or 1N295. The respective values are .01F input caps, scaling resistors are 4.1 Meg, 410 kOhms and 92 kOhms.
For audio sniffing, a probe with a .47 F input cap works quite well.
Calibration of an RF Probe using the Accuprobe is shown in a PDF file: RF Probe Calibration
NorCal Front

DC40 VXO Modification Odds and Ends A simple VXO consisting of a trimmer capacitor in series was added to the DC40 Transceiver from KD1JV and Hendricks QRP Kits. A PDF describing the details is located here:DC40 VXO PDF

Click here for a larger view. DC40 VXO Mod

DC40 Built in a CR-425 Enclosure Built this DC40 in a Crown Royal CR-425 for someone. Includes a switch to select the 7030 and 7040 crystals. Also includes my mini audio amplifier. Some folks find the DC40 audio a little weak and the amp provides a boost for earphones and a small speaker.

Click here for an inside view of the DC40 in the CR-425 enclosure DC40 in CR-425
DC40 in CR-425

Built in a
NEScaf in CR-425 Adjustable in center frequency and filter bandwidth, the NEScaf now has a permanent place in my shack's headphone circuit. The filter is a great addition to kit rigs that are without filters and adds capability even to those that do.

Click here for a larger view. NEScaf in CR-425


MRX-30 (MRX-40) Schematic

MRX-30 Schematic