[FoxHunt] Report 7/12/2000

Neil Pickford neilp@goldweb.com.au
Sun, 10 Dec 2000 16:21:29 +1000


Fox Hunt Report for Thursday 7th December 2000.

This Hunt took place in Weston Park Yarralumla starting at the Maze
carpark.
  
The Fox went on air at 6:45 pm and only one hound was at the 
meeting point.  John VK1ET set off on foot followed by Neil 
VK1KNP who decided to test an antenna and sniffer that was part 
of Tom VK1BUDs deceased estate.  Although Neil knew the location 
of the fox, normal techniques with TOM's antenna and the hand held 
did not work until we figured out it was a null type antenna.  

Two equal length folded dipoles connected antiphase with same 
length matching sections.  Even having figured out the principle 
did not help greatly as there is no front to back discrimination 
of the signal.

The fox had been placed on the far side of Yarralumla Nursery and
we encountered the chain mail fence which appeared to be radiating
the fox signal.  This further confused the readings out of the 
Null antenna.  As murphy's law would have it, we picked the long 
way around the fence ending up 1/2 way back to the starting 
location before clearing the obstacle at the lakes edge.  

After about 1/2 an hour the fox was located in a heap of garden 
mulch by John.  Neil was still trying to figure out the operation 
of Toms sniffer at this time.  

Tom's sniffer is an amplified tuned diode detector circuit with a 
large 1 ma analog meter.  The meter works well at showing the nulls 
but it takes a bit more practice to interpret the peaks.

John took the fox and hid it nearby, while Neil retuned and looked 
at the calibration of the sniffer.  Then Neil used Tom's equipment
to find the Fox.  All was going well with Neil following a strong 
null until he realised that he was DFing Black Mountain Tower, not
the Fox.  A quick retune of the sniffer yielded multiple null
directions, some towards Black Mt and others slightly divergent.
The divergent signals were followed and after a big spiral in on 
the fox location a mysterious heap of cut grass below a tree was
investigated, No Fox!  
Further Dfing showed the fox to be up the tree.  
Neil had been fooled by the obvious red herring John had placed.

It was found that pointing the folded ends of the the dipoles of 
the null type antenna directly at the source causes the null to 
disappear.  This can be used in the near field to determine if 
the fox is up or down.

Finally John had a try of Tom's equipment after Neil re-hid the fox. 
Similar problems with Black Mt were experienced drawing John well
off course.  Once John was within 40 m of the fox he began to get
better readings leading him to the base of a tree.  After searching
the grass, John found it hard to decide if the Fox was indeed up the
tree, however after some careful Null replotting he determined it
had to be in the grass, and this time found the Fox.

Neil and John retired for a BBQ after the 3rd Hunt.

This was probably the last Hunt for this year, although if there
is serious interest on the reflector I may schedule another one
before January 2001

All the best for Christmas
Neil VK1KNP