Archive for February, 2009

 This article is a reprint from my original article published in 2004. I don't use the antenna anymore (collecting dust in the basement) but the article will stay here for informational purposes. I live in an appartment and don't have the space to put up a large antenna for my Kenwood R1000 receiver. I knew the excistance of magnetic loops, but I never spent time to take a look at it. Why ? Who knows. For the main loop I used a soft copper tube, diameter is 10 mm, length about 3 meter. Try to make a circle (not always easy). A friend of me, Carl ON7NH, has drilled and tapped M3 tread into it. This makes it possible to use solder lips. The entire loop is constructed on a sunday afternoon. The smaller loop is about 60 cm in length (diameter 1/5 of the main loop), material is 1,5 square mm copperwire. With the capacitor found in my junkbox, I can tune the loop from 2,9 Mhz till 10 Mhz. Other capacitors will give other tuning ranges, have to experiment here.
This post is taken from my old website. I'm still dismantling that site. What is PMR446 anyway ? PMR446 stands for Personal Mobile Radio and is a license free radio in the 446 MHz UHF band. That is about 6 Mhz above the 70cm amateur radio band. There are 8 channels starting at 446.00625 MHz and ending at 446.09375, spaced 12.5 kHz apart. (more…)
Ham radio operators interested digital modes will often use these computer interfaces to automate CW contacts (send morse code from the PC), use the PC soundcard for RTTY and control push-to-talk functions among other things. Many of the PTT interface drawings  found on the net suffer the same problem. Well it is not really a problem.
Let's have a look at a typical interface :interface_before.jpg You have the RTS and DTR line tied together with diode, then comes a transistor that operates as a switch. And finally the ptt line from you transceiver. So when the RTS or DTR signal goes high, you are on the air. So what is the catch ? Ever booted your computer or used other software besides your regular hamradio soft ? Of course you did 🙂 and what happened ? My transceiver went in to TX on the wrong antenna / receive converter / mistuned antenna. Luckely the radio was set in SSB and no harm done without modulation. But it could be worse. interface_after.jpgSo what have I done ? A simple modification that costs almost nothing : add a simple switch in the PTT line. See the red switch in the interface drawing. That's it. When the computer has booted and ready to use, I toggle the switch and can operate the digital modes.
I just noticed in Google Analytics that I passed the 10,000 visitors benchmark. My blog started in March 2008 and I installed Analytics around March 22. So from March 22 2008 till now (Feb 3 2009) I had 10,381 visitors. About 75% comes from search engines and merely 18% via other sites. This is a figure that can be better. Work todo !