Updated 30th April 2003
Addendum and Errata to the LF Experimenter's Handbook
G3LNP Loop
Anyone building the pre-amp for the G3LNP loop should carefully look at the circuit diagram, which correctly shows TR3 and TR4 as NPN types. Unfortunately there is an error in the text, which describes them as PNP types. If you fit PNP types it may appear to work after a fashion, but you will probably be puzzled as to why it seems so bad!
I have built another copy of the G3LNP pre-amp for my basket weave litz loop (now finished - measured inductance 3.55mH). The reason for the LNP pre-amp is that it works well, is balanced so cancelling common-mode and thirdly allows me to do some direct comparisons with the LNP loop. It now works a treat, at least 6dB better than the LNP loop, even lying on its side amongst the filing cabinets and computers in the shack, but it is overloading the 7030, even with the 40dB attenuator
The LNP loop was designed to have a Q appropriate to the 136kHz band, whereas the litz loop has a Q well over 500 (not measured properly yet), consequently the tuning is very sharp.
John, G4CNN
That error gave me some grief when I built the loop pre amp. Incidentally, I had to remove the earth connection from the loop centre. Unknown to me , the loop support rod was near an underground power cable and caused a high level of induced noise. My loop is inside a garden shed about 25m from the operating position and I find no need for the rejection winding at this QTH. Mostly it gives better results than the main transmitter antenna.
Mike GW4HXO I have made some experimenting with the loop preamplifier described on page 29-30 in the Low Frequency Experimenters Handbook and below I share my results. In the evenings I have had severe cross modulation in the following way: Radio Sweden on 1179khz mixes with a station in Norway on 1314 and sometimes also with a station in Germany on 1044. Both giving a difference frequency of 135,0khz. The sidebands can be heard in the lower part of the lf-band and can be very strong in the evening with me, sometimes with the Swedish, Norwegian and German languages to be heard at the same time ! A wonderful experience ! How the MW signals come in to the preamp is a mystery as the amplifier is connected close to the loop and the loop Q is about 110. I have tried to suppress 1179 with a resonant circuit in various configurations however no change was noted. Anyway, I have changed the preamplifier circuit somewhat and the cross modulation now seems to have decreased a lot (not bothersome anymore) while the gain seems to be about the same (I have no means of measuring the gain). At least DCF has the same strength. Besides the mains noise seems to have decreased very much, possibly due to the much higher standing current in the FET:s.SM5EUF / Urban Date: 01 November 2002
G4GVC Receiver Converter
The source of the round can MC1496IC (MC1496 G) is specified. However this part seems to be difficult to find.
G0MRF has constructed this converter using a plastic packaged MC1496 and it works well once the pin connections have been sorted out. Details to follow when available.
PA0SE transmitter, page 3.6
The diagram of the PA0SE transmitter was not the one submitted by Dick for publication but an earlier diagram from Technical Topics in RadCom of January 1999.
The diagram on page 3.6 has a couple of errors. In addition modifications and improvements were introduced mainly to give protection to the power HEXFETs. The correct diagram is shown below.
Correct diagram of the PA0SE Transmitter
Dick, PA0SE
G0MRF
Transmitter, Fig 3.13, page 38:
1) The circuit published has two
resistors labelled R3. The resistor
connecting the 12V power supply to C9
and IC1 should be R5 (10R)
2) The circuit published has two
resistors labeled R30. The correct R30
connects from Pin 3 of IC7 to ground
(2k7). The other 'R30' located near S2
should be R39 (10k)
3) The polarity of capacitor C17 is
incorrect. The positive end should be
connected to the emitter of TR1.
4) "External VTO" should read
External VFO.
The Scopematch Tuning Aid', page 82 - 83.
The circuit diagram shows no 50ohm resistor connected across the 50t secondary of T1. The function of this resistor is to set the scale factor of the "I" output to 1V out = 1A in. The resistor is mentioned in the text, and is visible in the picture of Lech's unit (the three parallel R's), but is not shown in Fig 6.3. Not fitting this resistor will cause the voltage at the I output to be much higher than it should be - just how high depends on the ferrite core used for T1, but it could easily reach a few hundred volts. T2 does not require a load resistor.
Jim Moritz, M0BMU
Jim
has developed a new LF Tuning Meter that
uses two moving coil meters and does not
need an oscilloscope, see LFtunemeter.
NEW
Field
Strength Meter for the 137kHz Band, page
84. Fig
6.8. The values of both L1 and L2 should
be mH and not uH. Urban,
SM5EUF Appendix
1 "Earthing Resistance of
Antennae". page
89 The
former units to measure inductivity and
capacity were centimeters. For the
inductivity one Henry equals ten power
nine centimeters (not nineteen power
nine), a typo. The
equivalents may be expressed
alternatively as: Capacity:
one cm equals exactly ten by nine
picoFarad (ref. Fig 1a), or roughly one
picoFarad Inductivity:
one cm equals one nanoHenry page
90 Left
column, first paragraph should read
"T antenna with a capacity of 1050
centimeters" Right
column, second paragraph should read
"L antenna of mean height 142
m" which is the arithmetic mean
value of both tower heights (150m and
134m) as per Fig 2. "length 482
m" sum of lengths (352m and 130m)
as per Fig 2. "breadth at the end
500m" as per Fig 2. "and
capacity 15000 centimeters" as per
Fig 2. right
column, third paragraph the Fig 3
referred therein is not shown/printed
but is included below. Fig
3 from Appendix 1 Gamal
Soegiono RF
Current Meter Fig
6.1 shows a resistor of 12k in series
with the meter. This resistor should be
120k. The value is described correctly
in the text. Measurement
of Antenna System Impedance at LF A
method of extracting impedance data from
3-M data is described but the software
was not supplied. You
can now download a suitable program ZCALCB.EXE
from here. A description of its use is
contained within the text. For a full
set of programs (used to produce
the LF antenna impedance signature
shown in Fig 6.17) go to the home page
and select aegxtra. Calculations
of Coil Configuration for Maximum Q Value
of diameter to length ratio of a coil to
give maximum inductance (and supposedly
maximum Q) for a given length of wire -
derivation from classical formula for
single layer air-spaced coil M
= inductance of coil in microhenries D
= diameter of coil in inches N
= number of turns L
= length of coil in inches K
= turns per inch W
= length of wire used, in inches N
= W/p D
...............................................Equation
1 L
= N/K = W/p KD ......
..........................Equation 2 M
= D2N2/(18D + 40L)
............................Equation
3 (classical formula) From
Equations 1, 2 and 3: M
= (D2W2/p 2D2)
/(18D + 40W/ p KD) =
W2/(p 2(18D +
40W/p KD)) ..................Equation
4 dM/dD
= -W2p 2(18 - 40W/p KD2)/(18D
+ 40W/p KD)2) = 0 when M is a
maximum \
18 - 40W/p KD2 = 0 \
D2 = 40W/18p K
.....................................Equation
5 From
Equation 2 : D/L = D2Kp
/W ...........Equation 6 From
Equations 6 and 5: D/L
= 40WKp /18p KW = 40/18 = 2.22
for maximum inductance for any
length of wire of any number of turns
per inch, on a single layer, air-spaced
coil. A coil constructed in this most
efficient fashion, from a given length
of wire of given specification, should
therefore have the maximum attainable Q
for the system. (I could equally have
used metric units and the appropriate
classical formula.) This
result is not too far from the value of
2.5 deduced from Bill Bower’s
experiments shown on page 1.21 to 1.23) J.
A. Lowe, G3XZX,
C15 should be 220 pF not nF.
The LED is shown upside down.
The resistor feeding bias to the BB104:s
has no value. However 100k is a good
choice which I have used in some other
projects.
