QRP Labs Ultimate LPF User manual

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Ultimate LPF kit: Relay-switched LPF kit
PCB Revision 4
1. Introduction
Thank you for purchasing the QRP Labs relay-switched low-pass filter (LPF) kit.
This kit is designed to complement the Ultimate3 QRSS/WSPR kit but could also be used on its own at the
output of a homebrew QRP transmitter. The kit consists of a PCB that switches one of five LPF's between
the transmitter output and the antenna (the kit's “RF output”). This kit does not include the LPF's, it is
designed to accept the plug-in LPF filter kit, which is available separately (for bands 2200m, 600m, and ten
HF bands 160m – 10m).
Note that when used with the Ultimate3 QRSS/WSPR kit, the relay-switched LPF kit provides up to six
bands, each with its own relay-switched LPF. This is because the Ultimate3 kit contains space on its PCB
for fitting Relay 0 (band 0). Combined with the 5 LPF's on the relay-switched LPF kit PCB (band 1 to 5) this
allows for six LPF's.
2. Design
The circuit diagram of one of the LPF switching sections is shown to
the right (band 1). This circuit is simply repeated five times over, on
the relay-switched LPF kit PCB (bands 1 to 5). The same circuit also
exists once on the Ultimate3 QRSS/WSPR kit board (band 0).
Together, they provide six selectable bands for the Ultimate3
QRSS/WSPR kit.
The relay is a DPDT type (dual pole, dual throw). When the relay is
un-energised, the resting position is for both input and output of the
corresponding LPF to be shorted to ground. An LPF kit is plugged in
to the two 4-way sockets, shown here as SV3 and SV4.
When the relay is energised, the corresponding LPF is switched into
the circuit, connected between RF In and RF Out. In use, only one
relay should be energised at once time, to switch in the desired LPF.
The relays are miniature Panasonic RX2-5V types. With a height of
only 8.5mm, they are small enough to fit underneath the plug-in LPF
boards. The coil current is only 28mA and it can therefore be driven
directly by an AVR microcontroller output pin. A 1N4148 diode is
installed across the coil of each relay, to prevent high switching
voltages from damaging the microcontroller output.
The relay-switched LPF kit can be used in your homebrew QRP transceiver project too. One side of the
relay coils are connected to +5V. So to switch a relay, the appropriate band 1 to 5 input should be driven to
a low voltage to energise the relay coil. A transistor could also be used to switch each relay coil.
When used with the Ultimate3 QRSS/WSPR kit, you can either take the RF output from the original
connections on the Ultimate3 PCB, or from connections provided on the relay-switched LPF board.

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Note that the Rev 2/3/4 PCB allows the output side of each LPF / relay-switch to be connected
either to the common RF Output signal, or to individual connection pads. In this way, you can use
either a single antenna, or connect different antennas for each band. The choice is arranged by
wire jumpers, described below.
The Rev 4 PCB provides space for a vertical or edge-mounted SMA RF socket.
3. Parts List
RL1-RL5Panasonic TX2-5V relays. Six are supplied (five are installed on the LPF kit PCB, one is
provided for the installation on the Ultimate3 kit PCB)
D1-D5 1N4148 diode. Six are supplied (five are installed on the LPF kit PCB, one is provided for the
installation on the Ultimate3 kit PCB)
10 of 4-way female header sockets
1 of 10-way (2 x 5) female header socket
1 of 10-way (2 x 5) male header plug, extended (tall) size
4 of 25mm nylon hex spacers
1 of Printed circuit board, 80 x 37mm size
4. Construction
Please refer to the parts placement diagram below.
The order of construction is not important but a good principle to follow is to install the smaller components
first, so that the larger ones do not prevent easy access.
The following photographs show PCB Rev 1; later revisions are the same but have additional jumper pads
to facilitate the use of multiple antennas if required (described below). The Rev 2 PCB also has silk-screen
text labels “IN” and “OUT” to ensure that you plug in the low pass filter modules with the correct
orientation.

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One suggested order of construction is described in the following sections.
1) Solder in the five diodes D1-D5. Pay attention
to align the diodes correctly, according to the
stripe on the diode and the silk-screen of the
PCB.
2) Connect jumpers at each of the five relay
locations on the board, to connect the LPF
output either to the common RF output, or the
individual output for separate band antennas. You can use the offcuts from the diodes. I recommend
the jumpers at this stage, while they are still easily accessible, and not yet crowded by installed relays
and 4-way sockets. Another suggestion is to use a small loop, perhaps 5mm high, rather than lay the
jumper wire flat near the board. The small loop
will make the wire easier to change later, if you
need to. Please see the section below
describing these jumper options.
3) Fit and solder the five relays. Ensure that the
relay pins are straightened before inserting into
the PCB, as some may have become slightly
bent.
4) Fit and solder the ten 4-way sockets for the
LPF's. Ensure that they are pushed in properly
into the PCB, and at right-angles to the PCB.
One way to do this, is to plug in a constructed
LPF to ensure correct orientation of the
sockets, then solder them to the PCB.
Note that you should aim for more careful and
straight alignment than the slightly crooked
result shown here. It works, but is not pretty.
5) If using the LPF board with the Ultimate3
QRSS/WSPR kit, solder the 6th diode and
relay (for band 0) in place under the plug-in
LPF on the main Ultimate3 PCB. Note that if
you have previously fitted wire jumpers at W0-
W1 and W2-W3 on the main Ultimate3 PCB
(for standalone use WITHOUT the relay-
switched LPF board), then you need to remove
these wire jumpers now.
6) NOTE: Some of the tall 10-way (5 x 2) pin header connectors have been supplied with slightly
too long pins, 2-5mm too long. If you find this is the case, you can fit the header as described
below, and slide the plastic spacer down the pins, then cut off the few mm of excess using a
wire cutter. Alternatively QRP Labs can supply a replacement header, which is the correct
length. Usually the pin-cutting modification is easier and faster (no shipment time). Apologies if
you are affected by this manufacturing error.

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Fit the tall 10-way (5 x 2) pin header connector, pictured to the right, to the Ultimate3
PCB. The board photo (above right) shows the old (pre 6-Feb-2014 shipped kits)
board interconnect method, using the standard-height header. Insert the tall header
(right), with the short pins into the PCB, and the tall pins sticking up next to the relay.
Fit the 10-way (5 x 2) socket to the bottom side of the relay kit PCB (tracks side, not the components
side). This will mate with the long pins of the tall header fitted to the U3 PCB.
The easiest way to ensure that the plug and socket are perfectly aligned is to assemble the U3 and the
relay PCB in their final configuration, bolting the PCB's together using the 25-mm hex spacers, but
WITHOUT soldering yet. This will ensure correct orientation of all the connectors.
It will still help to temporarily remove the LCD from the U3, so that you can access the U3-side header
with your soldering iron.
When the two boards are bolted together and the connectors perfectly aligned, you can solder the 10-
way connectors.
Connection of wire jumpers
Please refer to the diagram below.

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The common RF output is available at the left and
right sides of the board. It is also connected to the
Band 0 output, the output of the Band 0 relay on
the main U3 board. Separate outputs Band 1 to
Band 5 are indicated on the diagram. The output
of each relay can be connected either to the
common RF output, or to the corresponding
individual band output.
The selection of common RF out or the individual
band output is achieved with jumper wires, in the
blue circled areas in the above diagram. The
centre connection should be wired to either the
right (for common RF out) or the left (for individual
band output). The example diagrams to the right
illustrate the connections for each case, for Band
4.
For the simple case, matching the earlier PCB revision 1, when all relay outputs are connected to the
same common antenna (the common RF Out), jumper all the central pads of each three, to the pad to its
right. This is shown in the left diagram, above.
SMA Connector for RF Output
The Rev 4. PCB features pads for soldering an SMA connector for
the common RF Output, if you wish, at the right side of the PCB.
There are pads for an edge-fitted SMA connector (shown coloured
green) or a vertical fitted type (blue). Alternatively you may still use
the existing two connection pads (Red-coloured, 0.1-inch pitch).
5. Operation
When used with the Ultimate3 kit, firmware version v3.02 or above
is required. Please refer to the appropriate operation manual for
your firmware version, for details.
The relay-switched LPF kit may also be used with the QRP Labs
Arduino shield kit.
6. Resources
Please see the kit page http://www.hanssummers.com/ultimatelpf for information on latest updates and
issues.
Please join the Yahoo forum http://groups.yahoo.com/neo/groups/QRPLabs/info for discussion and
updates on all the kits!

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7. Version History
114-Jan-2014
•Initial version
206-Feb-2014
•Modified PCB interconnection method, to use single tall-header plug on the U3 side, and single 10-
way socket on the relay board side.
328-Mar-2014
•PCB Rev 2: adds the jumper wire connections to allow connection of each relay output to either the
common RF output, or an individual band output pad.
416-Feb-2015
•Added page numbering
501-Jul-2015
•PCB Rev 4: adds pads for SMA connectors on right of PCB
609-Nov-2015
•Note about the few mm too long headers supplied in some Rev 4 kits.