ADDITIONS AND CORRECTIONS TO
DQ RECEIVER AND BEACON NOTES
Note that this page is updated frequently
the actual printed and posted notes, schematics, and layouts are always
a bit out of date!
- I have just completed 4 receivers (7/20/08), all of which
work. I used 5 Volt powered DVM's (the only ones available when I
ordered), which required some minor circuit changes. See the Notes on the
2008 DQ Receiver Boards for the changes and also for info on using
CR123A lithium cells for power.
- The parts list has been updated (4/14/08) after I actually placed
- These notes apply to boards with dates prior to 2008, as well as
to the DQ receiver portion of the new 2008 boards. They do not
apply to the new 2008 Class-E beacon.
- The new 2008 boards have only one change. U12 (and C42)
have been added to provide 9VDC for DVMs in the complete receiver that
cannot work on 12VDC. U12 is not shown on the schematic or the
front panel layout.
- Note that on the RF Amp board R20 (2M) has become R20A (1M) plus
in series. This is shown in the parts list and color layout, but not on
the schematic or on the actual circuit board.
- A good test of proper receiver operation is to disconnect the
the audio tone with RF gain at minimum, then increase RF gain in 32Hz
You should hear random noise from the RF amp as the RF gain is
- A simple way to test for proper shielding of the RF amplifier is
do the above test, then change to 1 Hz mode. With the receiver
nulled at minimum RF gain, slowly increase the RF gain while
The receiver should remain exactly nulled (check by rotating the null
up to the point where random noise masks it. For the complete
check with the gain switch in Hi and Lo positions. My receivers pass
test with the cover installed (and grounded), but fail with the cover
- Even in a properly shielded receiver, there is a small amount of
field radiation that can be detected by a nearby receive loop. To see
effect, audio null the receiver without the loop connected, then
the loop, set the receiver to high RF gain, and move the receiver near
the loop. Note that maximim coupling occurs when the receiver is near
flat side of the loop, ie near its axis. This coupling makes
difference when searching, but could cause a small "offset" in Ground
location. When doing the final, precise, locating, it is best to
squat down while holding the vertical receive loop at arms length ahead
of you, with the plane of the loop passing thru both you and the
- Another source for a varactor diode (with leads) that should work
Small Parts and kits. The part
no. is MV-209. It is listed as 32pF. Its spec
says 30pF at 3V reverse.
- I am told that Electronics Plus
a couple of leaded NTE-614 varactors. Dan's Small Parts has
leaded varactors that I haven't tried.
- NEW! If a 3 MHz crystal is used for
operation in countries with 50 Hz
power grids (to operate between harmonics), the operating freq will be
2929.69 Hz and the audio output will be 366 Hz instead of 437 Hz.
You must change the freq of the two audio bandpass filters to 366 Hz by
changing R15 and R45 (on the newer boards with two bandpass filters)
Ohms to 2.87k Ohms 1%.
- Once the loop is tuned for minimum DC current, the MOSFET will
without the added heat sink. Use very short ON periods (<5 seconds)
when doing initial tuning if the aluminum heatsink is not added.
Notes for Complete Receiver Only
Notes for Simplified Receiver Only
- On the schematic of the Complete Receiver, R19 is the 5.6k
for the Power-on LED.
- C31 and C32 (0.1uF B+ bypasses) were left off the Simplified
by mistake. They are shown correctly on the layout diagram.
- In the Simplified Receiver the Vcc power to the RF amp can be
directly to the on/off switch.
- The Simplified Receiver uses one 9V alkaline or can use a 12V
- Many items can be deleted from the "complete receiver" parts
list. Delete on detector board: the DVM, U2, U12, C42, V1, U11 &
SOCKET, R47, R48, R49, R50, R53, R54, U8 & SOCKET, R27, R28, R29,
R30, R31, R32, R33, R37, C21 (A & B), C22, C38, R37, R39, R40, R41,
R42, R43, D5, D7, S4, S6, PIEZO ALARM, R9 can be a 1-turn linear
pot. Delete on RF amp board: R55, R21, S3, R22 can be a 1-turn
audio taper pot. Also delete one 9 Volt battery socket.
This list may not be complete.