OK1RR DX & Contesting Page

Ham Radio web site dedicated to CW DX operating and contesting
Differential current sensor

A differential RF current sensor

A small dual loop antenna, in other words a differential RF current sensor is shown on the picture below. (Credits go to Chavdar Levkov, LZ1AQ) Another image shows my implementation – a compact version, made from PCB with conductors on both sides ’embroidered’ with vias. Gerber data available (download here). (as output connector use an

Audio transformers 600:600 ohms on eBay

Small, cheap and widely available chinese transformers are frequently used in digimode interfaces, however the documentation is very poor. Both primary and secondary consists of 800 turns of enameled 0.06 mm copper wire wound with double wire. It has DC resistance of 135 ohms +/- 20% and inductance of 290 mH +/- 20%, wound on

The TinyKeyer

The TinyKeyer

the (possibly) World's Smallest Fully-Featured CW Keyer with Computer Support



This keyer, based on Arduino design, employs the famous K3NG code. It can be used with any Windows/Linux/Mac logging or contesting software with Winkeyer USB (K1EL) support. The credit & big kudos goes to Anthony Good (Goody), K3NG, who did the tremendous work. It is a very small unit (outer dimensions 45 x 45 x 18.6 mm, appx. 1.8 x 1.8 x 0.73 in) which does not have any fancy options (a zillion of buttons, psychedelic flashing LED lights or cockatoo colored displays). It is intended for regular CW work and contesting with computer support, most of functions should be adjusted and operated via the computer. For standalone work an acoustic menu in command mode is used. Otherwise, only speed control knob and a mini LED indicating the command mode is on the front panel, nothing more.

Coaxial Cables

Coaxial Cable Power Ratings Maximum input power rating – Watts at (MHz) RG/U CABLE 1.0 10 50 100 200 400 900 1000 3000 5000 55, 6A, 212 4000 1500 800 550 360 250   150 65 50 8 MINI, 8X 4000 1500 800 550 360 250   150 65 50 8, 8A, 10A, 213 11000
Collins Mechanical Filter

Farewell Collins Mechanical Filters

FILTERED OUT FOREVER For many radio amateurs, it’s the end of an era: Rockwell Collins, which designed and manufactured mechanical filters for more than two generations of hams, has discontinued the filters’ production. The company posted on its website: “Over the past several years, we have seen a dramatic reduction in demand for narrowband analog
Debouncer in WX7G style

A Debouncer for Semiautomatic Speed Keys in WX7G style

Like many others, I have noticed an ugly, scratchy sound while using my Vibroplex Presentation bug. The unwanted artifact is affected by the contact setting but it is impossible to remove this completely. This problem is noticeable mostly with new “fast” transceivers like K3. My idea that this sound is caused by contact bouncing was

Coaxial Cable attenuation

10 mm dia Coaxial Cable attenuation   Aircom Plus RG 213 U H 2000  Flex Ecoflex 10 Ecoflex 10+ H 2010  MHz  dB/100 m  dB/100 m  dB/100 m  dB/100 m  dB/100 m  dB/100 m 5    0,9        0,8    0,9      7        1,0        0,97  10    1,2    1,8      1,2    1,3    1,20 
1 turn

How to sort unknown ferrite cores

Do a single loop through the core windows and measure the impedance with some sort of analyzer. Even an MFJ259B with a short connection to the jack will work well for this. If X=R someplace much higher, you can be sure it is a different mix. The Q=1 frequency, where X=R or where loss tangent