Monday, 20 March 2017

Lessons Learned

I spent Sunday afternoon making and installing a replacement 40/20 inverted V for the flimsy one I had put up in the fall.  Here is one lesson I learned...QRP low power with lightweight wires is all well and good for temporary use but it is not robust enough to last through a windy winter.  The work was going pretty well and the weather was just above freezing and sunny.  Great for antenna work.  I had to raise and lower the antenna 4 or 5 times for trimming before I got it to resonance on both bands but I'm not quite sure if it's there just yet because as I was raising it the final time, a knot I had tied in the string I was using as a hoist came untied leaving 2 feet of string hanging from the pulley 40' up.   I had now been fiddling with this antenna for few hours.  I should have quit for the day and addressed this at a later date.  I didn't.  All I needed to do was climb the tower and detach the "yardarm" which keeps the antenna away from the tower.  The pulley is on the end of it.  Not too challenging.  Climbed up and realized that I had the wrong socket in my pocket for the U-bolts.  Back down and back up.  I ran a fresh piece of string through the small pulley and tossed the spool down to the ground keeping the loose end with me.  This was very challenging as the sun was directly behind the pulley.  I was clinging to the tower and struggling with the string.  I was cursing but eventually I got it after a few minutes.  I climbed down with the loose end and attached it to the antenna and started raising it up.  Half way up it got stuck.  The string (which is Mason's string) is very thin and quite durable however it jumped off the wheel and got stuck between the wheel and the side plate. I always knew this was a risk but figured the chances were slim of it ever happening.  No such luck.  My blood pressure and frustration level was maxed out at this point.  Luckily I did not have the right rope on hand to finish the job properly.  This gave me a good excuse to leave the task for another day.  This is a hobby and is supposed to be enjoyable.  We learn in many ways...from reading or watching videos or being taught by someone but the lessons learned through trial and error (mixed with frustration and possibly pain) are the ones we will never forget.

Saturday, 18 March 2017

Battle of The Beams

No, I am not talking about Amateur Radio HF Beams but a more clever system used by the German Luftwaffe during WWII.  Let me step back for a moment.  About 10 years ago I listened to a fantastic presentation at the Kemptville Amateur Radio Group from Al Penney (VO1NO) on this topic and it intrigued me immensely.  I got some references from him and got a couple of books from the library.  I read them from cover to cover as it was so interesting.  I wanted to touch on the Battle of The Beams and more specifically the Knickebein here in case anyone else would be interested.

Back in the 1930s the Germans were using something called the Lorenz beam as a Navigational Aid at landing strips.  Simplified, this consisted of 2 antennas on either side of the runway with one transmitting "dits" and the other transmitting "dahs".  Each aircraft had a receiver for these transmissions.  An approaching aircraft would line up on the runway and he drifted too far left or right he would only hear the dits or only the dahs.  If he were centered on the runway he would hear both dits and dahs.  This worked well.  Here is an image from the Wikipedia Lorenz Beam page.

Jump ahead to WWII.  Bombers were slow large aircraft and were easy targets for anti-aircraft weapons so bombing raids were generally held under the cover of darkness.  The problem with this is that it made it very difficult for the bomber pilots to see their targets below.  The British had blackouts in place so that the town showed no light should bombers be overhead.  The bombing raids tended to take place during the full moon so there would be a lot better vision however this made the raids more predictable.  Nighttime flying was generally difficult with minimal navigational aids at their disposal.

What the Germans did was use the technology of the Lorenz beam and beef it up.  Very large directional antennas were built and high power was used to provide the German pilots with a secret navigational aid.  The antennas were aimed at a specific target and the pilots would fly so that they were on course by listening for the dits and the dahs.  The receivers had to be hidden very cleverly in the aircraft so that if a bomber were shot down their secret would not be discovered.  This method of flying at night and finding their targets was extremely clever and quite successful.  There were different versions and names of this system as well as different antennas as the system was improved.

Wartime generates a lot of technological advancements and the German/English air battle really spurred on the development of Radio and RADAR technologies including countermeasures such as jamming.  If this interests you as much as it did me you should look up the history of the Knickebein, Freya, and the Battle of the Beams.
Here are some links of interest on the subject:
Radar Recollections
PA0PD's page

Cheers for now,
Scott ve3vvf

Thursday, 9 March 2017

The Radio Room Clock

Along with maps I think Hams are particularly intrigued by a nice clock.  Of course we always want a clock to put UTC time on and what better way to do that than with a clock that is both a time keeper and a conversation piece.  For those who are not familiar with the radio room clock or have seen it but were unaware of its significance.  The clock is easily recognisable with its green and red colour wedges at the quarter-hour points of the clock face.

The origin of the radio room clock goes back to the early 20th century.  Following the sinking of the Titanic, it was decided that coastal and marine traffic all use 500 kHz as the communications frequency for Morse code traffic.  The problem with this is that it made it a very busy frequency.  If a ship were to send a distress call on 500 kHz it could be lost in the congestion.  To remedy this problem, the Service Regulation stated that "Coastal stations engaged in the transmission of long radiograms shall suspend the transmission at the end of each period of 15 minutes, and remain silent for a period of three minutes before resuming the transmission."  This would allow distress calls to be heard.  As an aid to radio room operators, clocks were designed with a red wedge at 15 minutes past the hour and 45 minutes past the hour.  You can see this in old photographs but in Black & White, of course.  In later years a second set of wedges was added to the clocks at the top and bottom of the hour but these wedges were green in colour.  These represented silent periods twice per hour on the 2182 kHz for voice distress calls.

In the 1990s, with the decrease of the commercial use of Morse code traffic on 500 kHz, it was being monitored less and less until 1999 when it was discontinued.  Today there are many companies that sell replicas of the Radio Room clock and I got one for myself from Amazon.  It is a fine addition to any shack and will often be a conversation piece.

Cheers es 72/73 de Scott