DEMI ABPM User guide

DEM ABPM

All Band Power Meter

10 KHz to 10 GHz low level power meter

PREFACE:

The DEM ABPM is the all band, portable power meter developed by W1GHZ and described
on his web site at http://www.w1ghz.org/new/DEM_ABPM_kit.pdf
before you start assembly of this kit. The paper titled “Portable RF Sniffer and Power Meter”
discusses the compilation of designs by W7ZOI, W7PUA, WW2R, and W1GHZ then explains the
evolution of the final product. The web page explains the circuits in detail providing individual test
data of the power detector circuits. The page also discuses the methods of calibration, and the
final use of the circuit when complete. Be sure to review the references at the end of the web page
for further technical information and data sheets of the power detector chips. Other circuit designs
are available at that site that will compliment this kit. Feel free to browse around for other ideas.

CIRCUIT DESCRIPTION:

Now called the DEM ABPM in the Down East Microwave Inc. catalog, are actually two

individual power detection circuits combined through a simple switch connected to a bar graph
voltage meter. It is all neatly place in an enclosure with a self contained battery to make a
complete portable RF power detecting device that fits in your pocket. The ABPM has two
individual inputs (SMA connectors) that are limited by the frequency response of the detector chips
they are connected too. The Bar graph display can be operated as a running bar graph or as
individual ascending / descending segments to conserve battery power. The ABPM also has an
external meter connection so that more precise “measurements of change” device may be used by
connecting a digital or analog voltmeter directly to the detector circuits. One of the references on
W1GHZ’s web site describes an audio tone indicator and how it can be used with this device.

As for the kit in general, all components, hardware, connectors, and assembly instructions
are the responsibility of Down East Microwave Inc. Please call us if you find any components
missing, broken, or incorrect. Please do not contact W1GHZ with complaints such as fit and form
or missing or damaged components. He is not employed by DEMI and has no control of the
contents of this kit. DEMI has agreed to compile and distribute this kit with the original circuit board
and components
functions, modifications, or further uses of the circuit, Paul will be happy to, If contacted through his
website at
line in regard to how you enjoyed this kit or any concerns on how DEMI is managing the
distribution of this kit to the armature radio public.

www.w1ghz.org.

available from the DEMI standard inventory

with any details concerning these maters. You may also drop him a

It is recommended reading

. If you wish to discuss circuit

/Kits/ABPM.doc 1 Rev. A 6/19/06

CIRCUIT BOARD ASSEMBLY:

The circuit board assembly is basic and straightforward but some hints and special notes
are worth paying attention too. Use only the schematic and component placement supplied with
this kit for the best results. Some designators and placements have been changed from the details
provided on the W1GHZ web site to accommodate the components actually used in this kit. Please
review all of the following notes and read this document through before starting assembly.

Circuit Board:

1. Screen printing for U2 is backwards on circuit board. Follow the component placements
used in this kit only!

2. Surface mount versions are used for C4 and C5. Their polarity is indicated on the
component placement. The leaded version positions of both will be vacant when assembly
is complete.

3. Connectors or header pins are not used for J3 and J4.

4. R3, C7 and C9 are mounted on the bottom side of the PCB. U3 is shown on the bottom
side placement for orientation of those components. U3 is mounted on the topside.

5. The bar graph is installed on the bottom side. Examine the display carefully. One corner
is slightly chamfered to indicate pin one. The chamfer is shown on both components
placements (top and bottom). The screening on the PCB does not indicate it.

6. U1, the LTC5508, will be the most difficult part to assemble in this kit. It is found in a foil
bag. It has six leads. The lettering on it is most difficult to read but is imperative that you do
for proper alignment. Once the IC is heated with any flux during soldering, the marking is
removed making it next to impossible to verify. You get one shot at aligning it correctly.

Actual Assembly:

Use the component list with both top and bottom component placement diagrams.

1. Start by installing U1. Use a magnifying lens to verify lead placement on the PCB and
the marking on the LTC5508 for alignment. Position and solder one outside leg only. Re­verify placement of leads on pads then solder opposite leg of IC. Be sure of placement
then solder the other four leads. Use solder wick to remove excess solder that may
bridge or bulge over. Clean with flux remover and test with ohmmeter for shorts. If you
have a short try solder wick again. If you are required to remove the IC from the PCB to
repair, it most likely will not survive. Call DEMI for a replacement.

2. Next, install the topside surface mount components.

3. Install U2-U4. Remember that the screening for U2 is backwards.

4. Install C8 with a 1 turn 3/16” loop in the lead that is installed in the pad that C7 and R3
are connected to. The loop is L1 on the schematic.

5. Install all other leaded components including VR1 and VR2.

6. Install bottom side surface mount components.

7. Install bar graph on bottom side. Remember the chamfer is pin 1.

8. Trial fit the SMA connectors before soldering (found in the hardware bag). You will need
to trim the center pin length and modify the ground pins slightly. You will also need to
remove some solder mask from the ground plane before soldering. Push the flange of
the SMA up against the PCB as close as possible or the board assembly will not fit in the
enclosure.

/Kits/ABPM.doc 2 Rev. A 6/19/06

COMPONENTS LIST

Component Bag: Resistors values are in Ohms and are ¼W leaded unless otherwise specified. “POT” =

Potentiometer. "ELC" = Electrolytic. “Chip” is surface mount components.

C1
C2
C3
C4
C5
C6
C7
C8
C9
C10

8.2ρF 50mil ATC
100ρF Chip (0805)

0.1µF Chip (0805)

1.0µF Tant Chip

1.0µF Tant Chip

0.1µF Chip (0805)
15ρF Chip (1206)
1000ρF leaded

0.1µF Chip (0805)

0.1µF Chip (0805)

C11
C12
C13
C14
R1
R2
R3
R4
R5
R6

0.1µF leaded
100 µF ELC

0.1µF leaded

0.1µF leaded
10KΩ
51Ω Chip (1206)
470Ω Chip (1206)
10Ω
18KΩ
470Ω

R7
R8
VR1
VR2
BAR 1 Bar graph display
U4 LM3914
U1 LTC5508
U2 78L05 reg
U3 AD8307
One ABPM Circuit Board

1.8KΩ

1.8KΩ
10KΩ Pot
500Ω Pot

Enclosure Assembly

Start by wiring the PC board using the wire chart provided below. Cut and tin all wires to
length then attach them to the “From” positions on the circuit board. All wiring is done on the
topside of the circuit board. There will be Red, Black, and some other color wire that is designated
“odd”. (Something other than red or black) Pins #1 of the J3 and J4 connectors are the holes on
the circuit board in the square pads. Pins #2 are the round pads. For the GND connection on the
circuit board, scrape some solder mask off the circuit board above the WW2R logo and attach it by
soldering. Check all connections and trim excess wire off from the bottom.

Wire Connection Table

WIRE SIZE FROM TO

#24 Red Teflon 3” +V on PCB ON/OFF switch
#24 odd Teflon 3-1/2" J4-1 VHF/UHF switch
#24 odd Teflon 3-1/2" J3-1 VHF/UHF switch
#24 odd Teflon 3" J3-2 Jack
#24 Black Teflon 3" GND Jack
#24 odd Teflon 3” J4-2 VHF/UHF switch
Black from Battery Clip NA -V on PCB
Red from Battery Clip NA ON/OFF switch

/Kits/ABPM.doc 3 Rev. A 6/19/06

Find the half of the enclosure that has the battery compartment in it. It will also have three
round holes on three different sides. Install the two switches and jack as shown. Then install the
battery clip leads through a hole in the battery compartment side (not a top hole!) closest to the
ON/OFF switch. Position the enclosure as shown on your workbench. Place the circuit board on
the bench on the ON/OFF switch side of the enclosure with the wires up and the SMA connectors
pointing in the same direction as the VHF/UHF switch. Do not install the circuit board in the other
half as of yet. Connect the wires from the circuit board to the switches, jack, and from the battery
clip as shown below. After wiring is complete, check all connections and verify all circuits by eye for
shorts or wire clipping debris. If circuit board looks ready, attach it in the other half of the enclosure
by aligning the SMA connectors with the holes in the enclosure then inserting the circuit board in
place. Check to see that the bar graph display is correctly positioned in the machined hole of the
enclosure. There is some play in the screw holes so the display could be misaligned. Attach the
board with four sheet metal screws keeping the bar graph positioned correctly.

Sw1

ON

F
H
U

2
w

S

F
H
V

To J4 - 1
To J4 - 2
To J3 - 1

D
N
G

o
T

J5

OFF

)

V

d

+

e

o

R

T

(
t
a

B
o

T

2

n
e
p

O

To J 3-

y

r

Batte

Battery Compartment Half

Hardware Bag Component list:

(4) #4 Sheet Screw (2) SPDT switch (3”) Black Teflon wire
(2) 1-Hole PCB Mount SMA (1) Battery Clip (3”) RED Teflon wire
(1) 2.5mm Plug (1) 2.5mm Jack (15”) #24 Odd Color Teflon wire
(1) Machined Enclosure

Testing and Operation:

If all connections are correctly made and a battery is connected, it should come to life. With
the switch on, verify that the 5 VDC regulator is operating. Then follow the setup instructions as
published by W1GHZ on his website.

/Kits/ABPM.doc 4 Rev. A 6/19/06

JP1

Practical ABPM Use :

As you use this versatile power indication device, you will find many uses for it during your
portable operations or at home. It can be used to check low-level transverter port output power or
used to measure low-level microwave transverter output. It may be used at higher levels with the
proper attenuation installed on the SMA connectors. With a “sniffer” type antennae installed on the
RF ports, it can detect transmit power radiating from an antenna system. You will find it to be most
sensitive to any RF environment it is used in from 10 KHz to 10 GHz.
We hope you have fun assembling and testing this kit and hope you have continued fun with
its use. Good Luck on the bands.

/Kits/ABPM.doc 5 Rev. A 6/19/06

Bottom Layout

7

3

C

R

/Kits/ABPM.doc 6 Rev. A 6/19/06

+

+

Mount on
bottom

ABPM Top PC Board Layout

/Kits/ABPM.doc 7 Rev. A 6/19/06

DEM ABPM KIT

All Band Power Meter

Assembly Notes and Pictures

Paul Wade W1GHZ [e-mail]

Down East Microwave has kindly agreed to make kits available for my All Band Power
Meter (Note: I receive no remuneration from these kits – I’m just happy that DEMI
makes them available). The assembly instructions are good, but photographs can help to
clarify things, so I put together a kit from DEMI, taking pictures and notes along the way.
These are intended to supplement the assembly instructions.

Step one of the assembly is the tricky bit – parts that work at 10 GHz are small! Once
you get U1 installed, there are a handful of surface-mount components, then the rest are
ordinary components with leads to stick through the holes and solder.

For U1 and the other surface-mount components, use a magnifying lens or microscope
and a pair of tweezers. A temperature-controlled soldering iron with a fine tip is
recommended, and the solder should be small diameter – I use 0.022” diameter no-clean
solder, like Multicore X39B.

Before any assembly, slip the two coax connectors in place and look where the grounding
legs will be soldered. I left the green soldermask too close around them, so scrape it
away with your X-Acto knife so that clean copper is available for soldering, then tin it
lightly.

Here is how I install U1: first I put a miniscule amount of flux in the PCB pads, by
dipping the lead of a ¼ watt resistor in rosin paste flux (Kester SP-44), the touching the
pads with that lead. Then I wet the pad connected to the input connecter (U1 pin6) with a
tiny dab of solder. I hold U1 (triple-check orientation) in place with the tweezers and
reflow the solder on that pad so that pin 6 is soldered in place. If the leads don’t all line
up, I reflow again and shift the part until they do. [An alternative here is to put a tiny dab
of temporary adhesive, like Blu-tac or Elmer’s Tac ‘N Stick, under the part to hold it
while soldering.] Once the part is in place with the leads aligned, I solder the leads one at
a time by putting the iron on the PCB pad next to the lead, then touch the iron with solder
and let it flow up the pad onto the lead. If it won’t flow or I bridge two leads, then I
come back after all the leads are done once and put solder-wick across all three leads on
one side of the part and heat the solder-wick with the iron. The flux in the solder-wick
will cause the solder to flow properly, and any excess solder will be soaked up by the
solder-wick. I’ve never had a bad assembly using this technique, but it leaves a lot of
flux residue to clean off.

At this point, you are either saying: “Sounds like I could do that” or “No way.” If you
find task daunting, enlist a friend or give Steve a call.

From here it gets easier. Step two, install the rest of the topside surface mount
components, using the above techniques, but these parts only have two, much bigger,
leads. It should look something like this:

Step three, install U2 through U4. Read the note again about the screening for U2 being
backwards – my fault. Make sure you get U3 and U4 correctly aligned also. If you
solder one in backwards, you’ll have to cut the leads off, pull them out one-by-one, clean
the holes, and call Steve for a replacement. I’ve never had a problem with U1, but did
get U4 backwards once.

Step four, install C8 with a loop in the lead for L1. You can see it in this picture of the
complete top-side assembly, with all the components added in step five.

Step six, install the bottom side surface mount components. Since there is no silkscreen
on the bottom to guide placement, I’ve added the designators to this photo. The photo
also shows the SMA connector in place, pointing out one grounding lug that must be cut
down to avoid shorting R3.

Step seven, install bar graph on bottom side, but don’t solder yet. Make sure the pin 1
chamfer is at the proper end, then slip the board into the top half of the plastic case. The
bar graph will sit recessed in the cutout. If you want it to sit higher, nearly flush with the
case, the leads must be pushed back into the board so it sits higher than the standoffs, as
shown in this picture:

Step eight, fit, trim, and solder the SMA connectors. This photo shows them on topside,
and the step six photo shows the bottom side of the VHF connector.

Enclosure assembly: the completed board photo is shown in step four above. Wires are
added according to the Wire Assembly Table, ending up with the board wired to the
bottom half of the enclosure like this:

Finally, slip the board into the top half of the enclosure and screw it down. It might look
like this last photo. Put the enclosure together, but hold it together with a rubber band for
now – the trimpots still need adjustment.

Calibration (from my previous paper)

The frequency response of these detector chips is not flat; there is some variation with
frequency, so any fine calibration must be at specific frequencies. For most purposes,
however, relative calibration within a few dB will suffice.

Fi g 8a: AD8307 Sensitivity

Uncompensated Compensated

3

2.5
2

1.5
1

Output Voltage

0.5
0

-90 -70 -50 -30 -10 10

Power in dBm

The two detectors have different sensitivity curves, shown in Figure 8. The AD8307
output is a straight line from about –70 dBm to about +5 dBm, a much greater dynamic
range than any commercial power meter.

Fig 8b: LTC5508 Sensitivity

1800

1600

1400

1200

1000

800

600

Output in millivolts

400

200

0

-30 -20 -10 0 10 20

Power in dBm

The straight line response of the AD8307 means that we can read power differences
directly, at 25 millivolts per dB. The LTC5508 does not have a linear response, nor is it
as sensitive, with a useful range of around –20 dBm to about +13 dBm, comparable to an
HP432 meter. So we have a combination of great sensitivity on the lower-frequency side
and great frequency response on the higher-frequency side.

The bar graph indicator is handy as a quick, no thinking required, indicator. Many times,
that’s all you need. Since the sensitivity curves in Figure 8 are so different, some
compromise is required for the LED bar graph to make sense for both detectors. The
output of the AD8307 may be loaded down, by R5 in the schematic to adjust the slope of
the response. I found that an 18K resistor gave similar full-scale readings for both
detectors. I set the “ZERO” pot (VR2) so that the first bar on the high-frequency side is
lit*, to provide a free pilot light, and set the “FULL SCALE” pot (VR1) to light at +10
dBm. Then I measured the response of both sides at 144 MHz, shown in this Table:

BARS Low Frequency High Frequency

1
2
3
4
5
6
7
8
9

10

Of course, you are free to adjust the calibration pots however you choose.

The LED indicator may be operated as a bargraph or as a series of dots, with only one
LED on at time. Since each LED draws about 20 mA., battery life will be much longer in
dot mode. The mode is selected by a jumper, J4, on the board.

When you are satisfied with the adjusments, screw the case together and apply the labels.
Then put it to work. One amusing test is how much power leaks through the closed door
of a microwave oven.

* In the kit unit, I had to change R6 to 100 ohms to get the first bar to light with no
signal.

One final option: if you would prefer higher sensitivity but don’t need the full frequency
range, an LTC5534 may be substituted at U1. This will provide roughly 60 dB of range,
but only up to about 3.5 GHz.

-70 dBm —

-59 -15 dBm

-51 -10

-43 -5

-35 0

-26 +3

-18 +6

-10 +7

-2 +9

+5 +10