http://www.lazygranch.com/images/radio/lv_3.gif

I've been experimenting with some homebrew direction finding gear,
namely loops and a Wellbrook amp. I have two loops, which for this
discussion will be called large and small. The large loop is about 2ft
on a side, and the small loop is about 1 ft on a side. The loops have a
platform to hold a compass, plus a handle to hold the loop. The handles
and compass platform are plastic. I use a magnifier over the compass to
minimize error. The compass is your basic Silva (about $10 at REI).

The beacon is 374Khz, located in Livermore, Ca. It backs right up to
hills on its east, which I'm sure adds nasty reflections.

The first measurement, point "1", is 2.4 miles from the beacon. I only
had the large loop at the time I did that measurement. The null was
very sharp.

I removed point "2" from the digram as the error was huge. I could not
get a decent null. At the time, I wasn't sure if the loop was the
problem, or the location. That was when I thought building a smaller
loop for comparison would be a good idea.

I used both the large and small loops at point "3". The null was good
with both loops, but clearly the smaller loop had less error.

At point 4, the large loop had a poor null, so I skipped the reading.
The small loop had 1 degree error.

I found that using the radio in CW mode with a narrow CW filter made
finding the null a bit easier.

Any ideas on how to improve the technique would be appreciated. The
goal of this exercise is to locate a beacon that is in a location where
deadly force is authorized, so I'll need accuracy from at least 10
miles away and probably not line of sight in all locations.

Buy an aircraft ADF receiver. The Bendix/King KR87 is an excellent
unit. Don't forget to install the loop antenna on a suitably large
groundplane and be sure to correct for QE (Quadrantal Error).

Brad.

"bradvk2qq" wrote in message
oups.com...
Buy an aircraft ADF receiver. The Bendix/King KR87 is an excellent
unit. Don't forget to install the loop antenna on a suitably large
groundplane and be sure to correct for QE (Quadrantal Error).

Brad.

A loop will not require a ground pane- in fact a local ground plane
(aircraft's conductive body) is what causes quadrantal error.
As long as your loop is well balanced, showing deep nulls, there should not
be a problem.
With my 7' rotatable shielded loop ( shielding serving the purpose of
balance, no improvement in S/N) I can see over 20dB nulls on ground wave AM
stations during the day.

Dale W4OP

"A loop will not require a ground pane- in fact a local ground plane
(aircraft's conductive body) is what causes quadrantal error. "



True, but an aircraft unit, anticipating a QE, already has a certain
amount of error built in, so even without a groundplane, the antenna
would still need to be swung to check for correct bearings. The beauty
of the system is that it does not rely on the interpretation of nulls
or S meter readings. It simply points directly to the station.

I cannot but think a GPS might be more accurate somehow!

Brad.

Metal objects like your vehicle, metal fences and those RR tracks can
cause errors as well. I can hear LV down here in SoCal most nights.
Usually a good signal. How about a foto of LV if you have visited the site?

Don

wrote:

http://www.lazygranch.com/images/radio/lv_3.gif

I've been experimenting with some homebrew direction finding gear,
namely loops and a Wellbrook amp. I have two loops, which for this
discussion will be called large and small. The large loop is about 2ft
on a side, and the small loop is about 1 ft on a side. The loops have a
platform to hold a compass, plus a handle to hold the loop. The handles
and compass platform are plastic. I use a magnifier over the compass to
minimize error. The compass is your basic Silva (about $10 at REI).

The beacon is 374Khz, located in Livermore, Ca. It backs right up to
hills on its east, which I'm sure adds nasty reflections.

The first measurement, point "1", is 2.4 miles from the beacon. I only
had the large loop at the time I did that measurement. The null was
very sharp.

I removed point "2" from the digram as the error was huge. I could not
get a decent null. At the time, I wasn't sure if the loop was the
problem, or the location. That was when I thought building a smaller
loop for comparison would be a good idea.

I used both the large and small loops at point "3". The null was good
with both loops, but clearly the smaller loop had less error.

At point 4, the large loop had a poor null, so I skipped the reading.
The small loop had 1 degree error.

I found that using the radio in CW mode with a narrow CW filter made
finding the null a bit easier.

Any ideas on how to improve the technique would be appreciated. The
goal of this exercise is to locate a beacon that is in a location where
deadly force is authorized, so I'll need accuracy from at least 10
miles away and probably not line of sight in all locations.

Sorry I missed your post. I'll make it a point to drive by the beacon
the next time I have a frame or two left on a roll. I should try the
smaller loop that seems less interference prone on that beacon in the
nearfield.

Don wrote:
Metal objects like your vehicle, metal fences and those RR tracks can
cause errors as well. I can hear LV down here in SoCal most nights.
Usually a good signal. How about a foto of LV if you have visited the site?

Don

wrote:

http://www.lazygranch.com/images/radio/lv_3.gif

I've been experimenting with some homebrew direction finding gear,
namely loops and a Wellbrook amp. I have two loops, which for this
discussion will be called large and small. The large loop is about 2ft
on a side, and the small loop is about 1 ft on a side. The loops have a
platform to hold a compass, plus a handle to hold the loop. The handles
and compass platform are plastic. I use a magnifier over the compass to
minimize error. The compass is your basic Silva (about $10 at REI).

The beacon is 374Khz, located in Livermore, Ca. It backs right up to
hills on its east, which I'm sure adds nasty reflections.

The first measurement, point "1", is 2.4 miles from the beacon. I only
had the large loop at the time I did that measurement. The null was
very sharp.

I removed point "2" from the digram as the error was huge. I could not
get a decent null. At the time, I wasn't sure if the loop was the
problem, or the location. That was when I thought building a smaller
loop for comparison would be a good idea.

I used both the large and small loops at point "3". The null was good
with both loops, but clearly the smaller loop had less error.

At point 4, the large loop had a poor null, so I skipped the reading.
The small loop had 1 degree error.

I found that using the radio in CW mode with a narrow CW filter made
finding the null a bit easier.

Any ideas on how to improve the technique would be appreciated. The
goal of this exercise is to locate a beacon that is in a location where
deadly force is authorized, so I'll need accuracy from at least 10
miles away and probably not line of sight in all locations.

M... "I was thinking maybe I can find some coax that will
fit tightly in copper pipe so that I could use a shield.
- - - Do you think that would help the null?"

Spacing - Copper Pipe Shielded Coax Cable Loop Antenna
http://groups.yahoo.com/group/Shortw...a/message/9878

Take a chunk of the Coax Cable and the Copper Pipe
and go down to a Home Depot, Lowes, ACE or OSH.

Find one or may be two sizes of Clear Plastic Tubing or
Clear Hose used for Refrigerators and Air Conditioners
that will fit around the Coax Cable and inside the Cooper
Pipe. Note - Do Not Use the Black and Colored Hoses.

As-an-Alternative - Take some Masking Tape {Plain Paper
Tape} [Do Not Use Silver Duct Tape] and Tape it around
the Coax Cable every Six Inches (6") to act as a "Spacer"
between the Coax Cable and the Copper Pipe.

# 1 - Having a 'uniform' "Spacing" between the Coax
Cable and the Copper Pipe will improve the Peak-and-Null
performance of the Loop Antenna.

# 2 - Plus having a 'uniform' "Spacing" between the
Coax Cable and the Copper Pipe will make the day-to-day
results from the Loop Antenna more consistent since
the Coax Cable will not be moving about inside the
Copper Pipe as the Loop Antenna is moved about in
Travel.

IMHO - "In Theory" -This is... Just Plain Common Sense }


hope this helps - iane ~ RHF