MFJ VEC-820K User manual

IMPORTANT WARRANTY INFORMATION! PLEASE READ
Return Policy on kits When Not Purchased Directly From Vectronics: Before continuing any
further with your VEC kit check with your Dealer about their return policy. If your Dealer
allows returns, your kit must be returned be
f
ore
y
ou begin construction.
Return Policy on kits VVhen Purchased Directly From Vectronics: Your VEC kit may be
returned to the factory in its pre-assembled condition only. The reason for this stipulation is,
once you begin installing and soldering parts, you essentially take over the role of the device's
manufacturer. From this point on, neither Vectronics nor its dealers can reasonably be held
accountable for the quality or the outcome of your work. Because of this, Vectronics cannot
accept return of any kit-in-progress or completed work as a warranty item for any reason
whatsoever. If you are a new or inexperienced kit builder, we urge you to read the manual
carefully and determine whether or not you're ready to take on the job. If you wish to change
your mind and return your kit, you may--but you must do it before you begin construction, and
within ten (10) working days of the time it arrives.
Vectronics Warrants: Your kit contains each item s
p
ecified in the
p
arts list.
Missing Parts: If you determine, during your pre-construction inventory, that any part is
missing, please contact Vectronics and we'll send the missing item to you free of charge.
However, before you contact Vectronics, please look carefully to confirm you haven't misread
the marking on one of the other items provided with the kit. Also, make certain an alternative
part hasn't been substituted for the item you're missing. If a specific part is no longer available,
or if Engineering has determined that an alternative component is more suitable, Vectronics
reserves the right to make substitutions at any time. In most cases, these changes will be clearly
noted in an addendum to the manual.
Defective Parts: Today's electronic parts are physically and electrically resilient, and defective
components are rare. However, if you discover an item during your pre-construction inventory
that's obviously broken or unserviceable, we'll replace it. Just return the part to Vectronics at
the address below accompanied with an explanation. Upon receipt, we'll test it. If it's defective
and appears unused, we'll ship you a new one right away at no charge.
Missing or Defective Parts After You Begin Assembly: Parts and materials lost or damaged
after construction begins are not covered under the terms of this warranty. However, most parts
supplied with VEC kits are relatively inexpensive and Vectronics can replace them for a
reasonable charge. Simply contact the factory with a complete description. We'll process your
order quickly and get you back on track.
Factory Repair After You Begin Assembly: Kits-in progress and completed kits are specifically
excluded from coverage by the Vectronics warranty. However, as a service to customers,
technicians are available to evaluate and repair malfunctioning kits for a minimum service fee
of $18.00 (1/2 hour rate) plus $7.00 shipping and handling (prices subject to change). To
qualify for repair service, your kit must be fully completed, unmodified, and the printed circuit
board assembled using rosin-core solder. In the event your repair will require more than an
hour to fix (or $36.00, subject to change), our technicians will contact you in advance by
telephone before performing the work. Defective units should be shipped prepaid to:
When shipping, pack your kit well and include the minimum payment plus shipping and
handling charges ($25.00 total). No work can be performed without pre-payment. Also, provide
a valid UPS return address and a day time phone number where you may be reached.

V
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INTRODUCTION
Thank you for purchasing the VEC-820K CW Filter kit. The VEC-820K consists
of a four stage, switch selectable band pass CW filter, using selected components
that will make "cleaning up" CW signals effortless and easy. With the VEC-
820K you bring up any hard to hear signal out of a "band pile up," for easy
listening, or get rid of unwanted, annoying signals. The VEC-820K also features
a headphone output that will allow the use of standard monoral headphones.
Although physically small in size, the VEC-820K is high on performance and
reliability. The VEC-820K is powered from a 9-volt transistor radio batterv.
TOOLS AND SUPPLIES
Construction Area: Kit construction requires a clean, smooth, and well-ighted
area where you can easily organize and handle small parts without losing them.
An inexpensive sheet of white poster board makes an excellent construction
surface. while providing protection for the underlying table or desk. Well-
diffused overhead lighting is a plus, and a supplemental highintensity desk lamp
will prove especially helpful for close-up work. Safety is an important
consideration. Be sure to use a suitable high-temperature stand for your soldering
iron. and keep the work area free of combustible clutter.
Universal Kit-building Tools: Although your particular kit may require
additional items to complete, virtually all construction projects require a work
area outfitted with the followin
g
tools and su
pp
lies:

VEC
-
820K Instruction Manual CW Filter
BEFORE YOU START BUILDING
Experience shows there are jour common mistakes builders make. Avoid these.
and
y
our kit will
p
robabl
y
work on the first tr
y
! Here's what the
y
are:
1. Installing the Wrong Part: It always pays to double-check each step. A 1K and
a 10K resistor may look almost the same, but they may act very differently in
an electronic circuit! Same for capacitors--a device marked 102 (or.001 uF)
may have very different operating characteristics from one marked 103 (or
.01uF
2. Installing Parts Backwards: Always check the polarity of electrolytic
capacitors to make sure the positive (+) lead goes in the (+) hole on the
circuit board. Transistors have a flat side or emitter tab to help you identify
the correct mounting position. ICs have a notch or dot at one end indicating
the correct direction of insertion. Diodes have a banded end indicating
correct polarity. Always double-check--especially before applying power to
the circuit!
3. Faulty Solder Connections: Inspect for cold-solder joints and solder bridges.
Cold solder joints happen when you don't fully heat the connection--or when
metallic corrosion and oxide contaminate a component lead or pad. Solder
bridges form when a trail of excess solder shorts pads or tracks together (see
Solder Tips below).
4. Omitting or Misreading a Part: This is easier to do than you might think!
Always double-check to make sure you completed each step in an assembly
se
q
uence.
Soldering Tips: Cleanliness and good heat distribution are the two secrets of
professional soldering. Before you install and solder each part, inspect leads or
pins for oxidation. If the metal surface is dull, sand with fine emery paper until
shiny. Also, clean the oxidation and excess solder from the soldering iron tip to
allow maximum heat transfer. Allow the tip of your iron to contact both the lead
and pad for about one second (count "one-thousand-one") before feeding solder
to the connection. Surfaces must become hot enough for solder to flow smoothly.
Feed solder to the opposite side of the lead from your iron tip--solder will wick
around the lead toward the tip, wetting all exposed surfaces. Apply solder
sparingly, and do not touch solder directly to the hot iron tip to promote rapid
melting.
Desoldering Tips: If you make a mistake and need to remove a part, follow these
instructions carefully! First, grasp the component with a pair of hemostats or
needle-nose pliers. Heat the pad beneath the lead you intend to extract, and pull
g
entl
y
. The lead should come out. Re
p
eat for the other lead.

VEC-820K Instruction Manual CW Filter Kit
orientation. Many specialized diodes and low-current voltage regulators also use
this type packaging. Larger plastic transistors and voltage regulators use a case
backed with a prominent metal tab to dissipate heat (T-220). Here
orientation is indicated by the positioning of the cooling tab.
Integrated Circuits: Proper IC positioning is indicated by a dot or square
marking located on one end of the device. A corresponding mark will be silk-
screened on the PC board and printed on the kit's parts-placement diagram. To
identify specific IC pin numbers for testing purposes, see the diagram below.
Pin numbers always start at the keyed end of the case and progress counter-
clockwise around the device, as shown:

VEC-820K Instruction I Manual CW Filter Kit
PARTS
Your kit should contain all of the parts listed below. Please go through the parts
bag to identifyand inventory each item on the checklist before you start
building, If any parts are missing or damaged, refer to the warranty section of
this manual for replacement instructions. If you can't positively identify,an
unfamiliar item in the bag on the basis of the information given, set it aside until
all other items are checked off. You may then be able to identify it by process of
elimination, Finally, your kit will go together more smoothly if parts are
organized by type and arranged by value ahead of time, Use this inventory as an
opportunity to sort and arrange parts so you can identify and find them quickly.
©Qty Part Description Designation
6 24.3K* ohm resistor (red-yellow-orange-brown) R9,R10,R12 1,R12.
R13,R14
-4 681 K* resistor (blue-gray-brown-orange) R5, R6. R7, R8
4 1.82M* ohm resistor (brown-gray-red-yellow) RI, R2. R3, R-4
8 1000 pF poly capacitor (1000J) C1,C2,C3,C4,C5,C6
C7,C8
1 01 uF disc ceramic capacitor (103Z) C9
2 10 uF electrolytic capacitor (10uf) CIO, c1 I
2 1-4 pin IC sockets For U1. U2
2 LM747 Op Amp IC U l . U2
I 4P4T Slide Switch with screws SW l
6 6" Insulated wires Circuit wiring
I 9-volt batter, snap GND. VCC
1PC board VEC-820K
1Owner's Manual
" These parts have a 1% tolerance, The tourth color band on these
com
p
onents will BROWN, s
p
ecif
y
in
g
a l% tolerance.
b

[
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EC
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Filter
STEP-BY-STEP ASSEMBLY
Before assembling your kit, please take time to read and understand the VEC kit
warranty printed on the inside cover of this manual. Also, read through the
assembly instructions to make sure the kit does not exceed your skill level. Once
you begin construction, your kit will be non-returnable. Finally, if you haven't
already done so, please verify that all parts listed in the inventory are included.
If anything is missing or broken, refer to the warranty instructions for
replacing missing or damaged parts.
Note that part designators. such as R1, C3, etc., appear on a silk-screened legend
on the component-mounting side of the printed circuit board. This corresponds
with the parts placement page in the manual. All parts will be inserted on the
silk-screen side of the board.
If you have last-minute questions about what you need to build your kit, please
refer back to the section titled "Tools and Supplies". If you're ready to begin
now. here we go! The directions use two sets of check boxes. Check one when a
step is complete and use the other for double-checking your work before
operation.
Important Note: Capacitors Cl-C8 are made of a polystyrene type material. Avoid
overheating these components when soldering to prevent melting the capacitor
bod
y
.
1. Locate capacitor C 1 (1000pF). This is a polystyrene capacitor and
will be marked with a "1000P on the bod
y
(
actual value in
p
F
)
.
2. Mount C l and solder both leads in place, making sure the capacitor
remains seated, Remove excess leads on the bottom side of the board
with dia
g
onal cutters.
3. Locate capacitor C2 (1000 pF). This is another polystyrene capacitor.
and it will be marked with a "1000J" (actual value in pF). Carefully
install C2 in the same manner as C1
,
and solder in
p
lace.
4. Locate capacitor C3 (1000pF). This is another polystyrene capacitor and
it will also be marked "1000T' (actual value in pF). Carefully install C3
in the same manner as C2, and solder in place.
5. Locate capacitor C4 (1000pF). This is another polystyrene capacitor and
will be marked "1000J" (actual value in pF). Carefully install C4 in the
same manner as C3
,
and solder in
p
lace.
6. Locate capacitor C5 (1000pF). This is yet another polystyrene capacitor
and will be marked "1000J" (actual value in pF). Carefully install C5
in the same manner as C4
,
and solder in
p
lace.

1'EC-820K Instruction a
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7. Locate capacitor C6 (1000pF). This is yet another polystyrene capacitor
and will be marked "1000J" (actual value in pF). Carefully install C6 in the
same manner as C5
,
and solder in
p
lace.
8. Locate capacitor C7 (1000pF). This is yet another polystyrene
capacitor and will be marked "1000J" (actual value in pF). Carefully install
C7 in the same manner as C6
,
and solder in
p
lace.
9. Locate capacitor C8 (1000pF). This is the final polystyrene capacitor
and will be marked "1000J" (actual value in pF). Carefully install C8 in the
same manner as C7, and solder in place.
10. Locate capacitor C9 (.0luF). This is a disc ceramic type capacitor and
will be marked "103" or "103Z" (actual value in uF). Carefully install C9.
ensuring not to chip the ceramic material. Once installed, then solder in
p
lace.
11. Locate resistor R1. This is a 1.82M resistor (brown-gray-red-N-ellow
brown
)
.
Carefully bend the leads close to the resistor body to form right-angles (see
followin
g
dia
g
ram).
12. Insert RI into its mounting holes so the resistor body rests against the
board. Solder in place and trim the leads.
13. Locate resistor R2. This is a 1.82M resistor (brown-gray-red yellow-
brown). Carefully bend the leads close to the resistor body as in Step
#11.
14. Insert R2 into its mounting holes so the resistor body rests against
the board. Solder in place and trim the leads.
15. Locate resistor R3. This is a 1.82M resistor (brown-gray-red-
yellow brown). Carefully bend the leads close to the resistor body as in
Step #11
16. Insert R3 into its mounting holes so the resistor body rests against
the board. Solder in place and trim the leads.

17 (
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820K Instruclion .Manual Cff
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Filter
17. Loca,td r"c'sistor R4. This is a 1.82M resistor (brown-gray-red-Nellmc
brotk W). "~'arefiilly bend the leads close to the resistor body as in Step
#11.
20. Insert R> into its mounting holes so the resistor body rests against the
board. Solder in place and trim theleads
"
21 Locate resistor R6. This is a 681K resistor, (blue-gray-brown-orange
brown). Carefully bend the leads close to the resistor
body.as in Step #1l.
22. Insert R6 into its mounting holes so the resistor body rests-against the
board. Solder in place and trim the leads.
23. Locate resistor R7. This is a 681K resistor (blue
-
gray
-
brown
-
orange
broN%n). Carefully bend the leads close to the resistor body as in Step
#11
24 Insert R7 into its mounting holes so the resistor body rests against the
board. Solder in place and trim the leads.
25. Locate resistor R8. This is a 681K resistor (blue-gray-brown-orange-
broL%n). Carefully bend the leads close to the resistor body as in Step #1 l.
26. Insert R8 into its mounting holes so the resistonbody rests against the
board. Solder in place and trim the leads.
27. Locate resistor R9. This is a 24.3K resistor (red-yellow-orange-red-
brown). Carefully bend the leads close to the resistot body as in Step #11.
28. Insert R9 into its mounting holes so the resistor body rests against the
board. Solder in place and trim the leads.
29. Locate resistor R10. This is a 24.3K resistor (red-yellow-orange-red-
brown). Carefully bend the leads close to the resistor body as in Step #11.
1

F EC-820K Instruction A
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30. Insert RIO into its mounting holes so the resistor body rests against the
board. Solder in
p
lace and trim the leads.
31. Locate resistor R11. This is 24.3K resistor (red-yellow-orange-red-
brown). Carefully bend the leads close to the resistor body as in Step #I1.
32. Insert RI 1 into its mounting holes so the resistor body rests against the
board. Solder in
p
lace and trim the leads.
33. Locate resistor R12. This is 24.3K resistor (red -yellow-orange-red-
bro,yn). Carefully bend the leads close to the resistor body as in Step
#11.
34. Insert R12 into its mounting holes so the resistor bod_N rests against
the board. Solder in
p
lace and trim the leads.
35. Locate resistor R13. This is 24.3K resistor (red-yellow-orange-red-
brown). Carefully bend the leads close to the resistor body as in Step #11.
36. Insert R13 into its mounting holes so the resistor body rests against the
board. Solder in
p
lace and trim the leads.
37. Locate resistor R14 This is 24.3K resistor (red-yellow-orange-red-
brown). Carefully bend the leads close to the resistor body as in Step #11.
38. Insert R14 into its mounting holes so the resistor body rests against the
board. Solder in place and trim the leads. Save the excess trimmed pieces of
resistor lead. You will need it later.
39. Locate a G" length piece of insulated wire. and cut piece 1 1/4" long off
of it
40. Using the wire strippers, remove 1/4" of insulation from each end of the
1 1/4" wire.
42. Solder the 1 1/4" wire in place at JNIP2 and trim the excess wire.
43. Locate the
p
ieces of excess resistor lead
y
ou saved back in ste
p
#38.
44. Install the excess lead in the holes located at JNIP I on the circuit
board. Solder in
p
lace and trim the excess lead.
41. Insert the bare ends of the 1 1/4" wire into the holes on the circuit
board located at JMP2. Please refer to the section titled "Parts Placement".
Fi
g
ure 1 for the location of
J
NIP2.

ITC
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Filter
45. Locate capacitor CIO (IOuF). This is an electrolytic type capacitor
and will be marked "lOuF" (actual value in uF). Carefully install C9:
be sure to orient the negative end of the capacitor properly. Please
refer to the section titled, "Parts Placement", Figure I for correct
orientation of CIO. Once installed, then solder in place and trim
excess lead.
46. Take the remaing 6" lengths of insulated wire and cut them in half.
You should have (10) 3
"
pieces of insulated wire.
47. Using the iyire strippers. remove a 1/-1" piece of insulation from
each of the 10 pieces of insulated wire .
48. Take a 3" piece of insulated wire and insert one end into the hole
silk-screened INPUT on the circuit board. Solder in place and trim the
excess lead
49. Take one 3" piece of insulated wire and insert one end into the hole
silk-screened #1 on the circuit board. Solder in place and trim the excess
lead.
50. Take one 3" piece of insulated wire and insert one end into the hole
silk-screened #2 on the circuit board. Solder in place and trim the
excesslead.
51. Take one 3" piece of insulated wire and insert one end into the hole
silk-screened #3 on the circuit board. Solder in place and trim the excess
lead.
52. Locate the battery snap. Insert the RED lead into the hole silk-
screened VCC on the circuit board. Solder in place and trim the excess
lead.
53. Insert the BLACK lead of the battery into the hole silk-screened GND
on the circuit board. Solder in
p
lace and trim the excess lead.
54. Locate the 4P-1T slide switch
(
S W
55. Inspect the slide switch for tarnished contacts. Remove any tarnish
with very fine sandpaper so the contacts are nice and shiny. This will
provide a good soldering surface.
Note: Please refer to the section titled, "Parts Placement" Figure 2 for Steps 56
throu
g
h 66.
56. Connect one 3" piece of insulated wire to Point A on SW1. Do
not solder yet.
1

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57. Connect the other end of the insulated wire located at the INPUT
location on the circuit board to Point A on SW 1. Solder in place and trim
the excess lead from the switch contact.
58. Locate capacitor C 11 (1 Ouf . This is an electrolytic type capacitor
and will be marked "IOuF" with an arrow pointing to the negative
end.
59. Trim the positive lead of C 11 so about only 3/8" of the lead
60. Connect the positive lead of C 11 at Point B on SW 1. Do not solder
this switch contact yet.
61. Connect the other end of the insulated %sire located at #3 on the
circuit board at Point Con SW l. Solder in place and trim the excess lead
from the switch contact.
62. Connect the other end of the insulated wire located at #2 on the
circuit board at Point D on SW 1. Solder in place and trim the excess lead
from the switch contact.
63. Connect the other end of the insulated wire located at #1 on the
circuit board at Point F on SW I. Solder in place and trim the excess
lead from the sNvtich contact.
64. Cut a 1 1/4"
p
iece of wire from one of the remainin
g
3"
65. Using the wire strippers. remove a 1/4" piece of the insulation from
each end of the 1 1/4" wire.
66. Connect the t t/4" piece of wire between Points B and E on SW l.
Solder in
p
lace and trim the excess lead from the switch contact.
67. Locate (1) 14
p
in IC socket.
68. Install the IC socket at the UI location on the circuit board. Be
careful to orient the socket correctly according to the "Parts Placement"
section Fi
g
ure 1.
69. Carefully bend over the four corner pins of the socket against the
solder pads on the solder side of the board. Solder in place.
70. Locate the remainin
g
14
p
in IC socket.
71. Install the IC socket at the U2 location on the circuit board. Be
careful to orient the socket correctly according to the "Parts Placement"
section Figure 1.
1

sockets for U 1 and U2. Please refer to the "Parts Placement" section.
Figure 1 for proper orientation. Be sure not to bend any of the pins
underneath the IC body, and that all pins are inserted into the socket.
At this point, your kit is finished and it's time to take a well-earned break!
When you come back. be sure to give your work a close "quality control"
inspection.
PC Board Ins
p
ection:
Before applying power to your kit, give it a thorough QC (quality control)
inspection. This xyill help you find inadvertent assembly errors that might
prevent the filter from working or cause damage to sensitive parts. Follow this
procedure:
Compare parts locations against the parts-placement diagram. Was each
part installed where it is supposed to be? Was the correct value used? Start
at one side of the board and work your way across in an organized
pattern.
I] Inspect the solder side of the board for cold-solder joints and solder
bridges betNycen tracks or pads. Use a magnifying glass to obtain a clear
view of the track area. If you suspect a solder bridge, hold the
board in front of a bright light for a better view. All joints should be
smooth and shiny. indicating good solder wetting and flow. Resolder any
beaded or dullappearing connections.
If you find a construction error and need to remove a part or two, it will be
easier if you have the right tools. One very convenient item for freeing
soldered-in parts is a "solder sucker". This consists of a suction bulb or a
spring loaded vacuum pump that draws molten solder away from the pad and
lead. Alternatively. you may use a special copper braid called "solder wick"
(solder suckers and solder wick are both available at your local Radio Shack or
electronics supply house). If you suspect you've damaged a component during
removal, better to replace it than risk reusing it!
Finally, rosin flux can absorb moisture, which may cause a problem for some
electronic equipment. To remove flux, use isopropyl alcohol (or 95% grain
alcohol) and an old toothbrush. Apply a generous amount of alcohol with the
toothbrush and scrub gently. Once the flux has fully dissolved, blot the bottom
of the board dry with an untreated tissue. Give it a final alcohol wash, and
allow to dry thoroughly.
1

CAUTION: ALCOHOL IS HIGHLY FLAMMABLE AND MUST BE USED WITH
ADEQUATE VENTILATION! USE SAFETY GOGGLES, AND
AVOID PROLONGED SKIN CONTACT. IT'S ALSO BEST TO DO
THIS OUTDOORS.
Now that assembly and inspection is completed, you're ready to begin the testing
and ali
g
nment
p
hase of construction.
The best way to test the VEC-820K is with a calibrated audio signal generator and
oscilloscope. However. VEC-820K does not require any alignment. If all
components are installed correctly and in the proper places, the center frequency
of the filter will be between 750-800 hertz. The filter has three switch selectable
selectivity cutoff points, 80, 110. and 180 hertz_. The switch positions on
SWl from left to right are BYPASS. 180. 110, and 80. The 80 hertz cutoff is the
fourth switch position from the left and is the narrowest filter cutoff. while the
180 hertz cutoff is the second position from the left and is the N%idest filter
cutoff.
Probably the best method of seeing if the VEC-820K is working, or not, is to
listen to some "on the air" CW signals. Then using SW1, select the filter cutoff
position that best cleans up the signal being received.
If you are trying to pick one signal out of a very tight band pile up, then try using
the 80 hertz cutoff. The 80 hertz cutoff provides the highest selectivity and will
greatly help you in "pulling out" those hard to get signals.
If the CW signal you are receiving is noisy with some static, then trv either the
110 or 180 filter cutoffs. However, in these positions the filter will let slightly
more noise through. but in some cases this may be desirable. The best way to see
which position works the best is to try it. This way you can really hear what the
filter is doing for the received signal, and which switch position works the best in
different band conditions.
1

You may use the VEC-820K with any communications receiver or scanner with
a BFO (Beat Frequency Oscillator). You can also use the VEC-820K with a
ham-radio transceiver in either LSB or CW mode. The VEC-820K requires a 9-
volt battery power source.
There are a few items that you will need to operate the VEC-820K. We have
p
rovided a list of these items below for
y
our convience.
Communications Receiver, scanner. or Ham Radio transceiver Nyith
proper cables.
0 9-Volt transistor radio batten
External s
p
eaker with cli
p
Receiver or Scanner
As mentioned above . you can use the VEC-820K with a communications
receiver or scanner. The receiver or scanner must be equipped with a BFO, or
Beat Frequency Oscillator. The BFO will allow you to fine tune the received
CW signal to the VEC-820 center frequency. The center frequency of the filter
being 750-800 hertz.
The filter requires audio from the external speaker or headphones output of the
receiver or scanner. This positive side of the audio signal is applied to the
insulated Nyire connected to Point A on SW 1. Apply the negative side of the
audio to the negative side of the battery snap. Please refer to the "Parts
Placement" section, Figure 2 for the location of Point A on SW 1.
Nest, connect the POSITIVE lead of the external speaker to the NEGATIVE end
of C11. Please refer to the "Parts Placement" section Figure 3 for the location of
C 11. Connect the NEGATIVE lead of the external speaker to the point labeled
GND on the circuit board. Again please refer to the "Parts Placement" section
Figure 1 for the location of the point labeled GND on the circuit board.
Nest, turn the receiver volume all the way down, then clip the 9-volt battery to
battery snap. Set SW1 to the far left position. Now turn the receiver up slightly
so you can hear the received signals on the external speaker. The signal you are
listening to is the "raw" or "unfiltered" signal. Using the tuning knob on the
radio find a CW signal. A good place to find CW signals is in the Amateur
Radio bands. Once you find a CW signal switch SW I to the 110 filter cutoff.
The 110 position is the third from the left. When you switch to the 110 cutoff,
you will notice that the signal sounds cleaner than before. You can now fine
tune the radio tuning knob for the best received signal. If using a
1

I E('-830/: Instruction _Manual Cll' Filter
communications receiver or scanner with a BFO control. use this control to
fine tune the received CW signal. If the receiver or scanner you are using does
not have a BFO control, it will be very difficult trying to tune the signal in
properly.
If the signal you are trying to receive is in a "pile up", then try the 80 hertz
filter cutoff. Then fine tune the receiver to "
p
ull out" the desired si
g
nal.
Operation with an Amateur Radio transceiver is basically the same, but you
would use either LSB (Lower Side Band) or CW mode. All other connections
arc the same.
IN CASE OF DIFFICULTY
No Si
g
nal Filterin
g
:
A neNyly constricted filter that fails to work upon initial power up. generally requires
a ver< close and careful inspection of all work. Please go back through all steps of
assembly and inspection. referring to the "Parts Placement" Figures
1. 2. and 3. Most of the time there will be a part that is not installed or not installed
properly. a wrong value part in place of another. or a broken part. A close
inspection at this point will reveal some accidental mistake.
Intermittent Filter O
p
eration
A filter that operates intermittently may have poor solder connections. a
problem Nyith broken wires, or low voltage power source. Self-oscillation.
may be caused b_v a defective U1 or U2. Also check for dirty or intermittent
switch operation.
Filter Sto
p
s Filterin
g
:
A working filter that fails "in-service" generally indicates a failure of in one or
both U l or U2. If you suspect a bad U 1 or U2. then do not touch the part
with your fingers. If the part is bad, it could be HOT and could cause a serious
burn. Other things that should be checked is the supply voltage of the 9-volt
batten
'
. broken wires to and from the circuit board and switch.
No S
p
eaker Audio:
No speaker audio can be a symptom of a bad SW 1, a broken Nvire or a bad C
11. Check the voltage from the 9-volt battery. A broken Nvire at the audio
in
p
ut to the filter can also attribute to no s
p
eaker audio.
If technical assistance or factory repair is desired, please refer to the warranty
instructions on the inside front cover
1

I
.
f
.
(
'-
820K Instruction Ilanual 01
"
Filter
THEORY OF OPERATION AND SPECIFICATIONS
Circuit Descri
p
tion:
The VEC-820K uses two UA747 operational amplifier integrated circuits to
form four low Q cascaded stages NNith no insertion loss. This results in a ven
narrow band« idth and extremely high skirt rejection with minimum audible
ringing. making good signal copying possible. The center frequency is
betNNeen 7
50
-
800
hertz. The filter is able to dri
v
e an
8
ohm s
p
eaker or
S
p
ecifications:
Bandwidth:.. .................................80 Hz
,
110 Hz
,
180 Hz
(
sNNitch
Skirt Re_jcolon:..................... ......... At least 60dB do%Nn 1 octave from
center frequency for 80 Hz. bandxN
ENCLOSURE
Vectronics has designed a matching enclosure just for your
CIF Audio Filler Kit. The matching enclosure is an all
includes knobs. hard\\are. decals. and rubber feet. The
number for the matching enclosure is VFC
-
820KC.
VEC-820K Super
metal box which
Vectronics model