Minikits EME157B2 User manual

SPECIFICATIONS: EME157B2 KIT
Frequency Range: Tuneable 120 to 150MHz
Bandwidth: 5MHz @ 3dB, ( depends on input tuning )
Gain: Typically 16dB Gain with –6dB onboard attenuator fitted
Noise Figure: <1.5dB Typically 1.15dB ( Includes Relays )
Tested with a HP8970B / HP346B
Through Loss: 0.05dB maximum at 145MHz ( Bypass Mode )
Power Handling: 100Watts Carrier ( +50dBm )
Power Supply +11 to 15vdc @ 100mA
Size: PC Board 66.7 x 83 x 25mm
Kit Webpage: www.minikits.com.au/eme157.htm
DESCRIPTION: The Pre-amplifier has been designed to be
easy to construct, and can be centre frequency tuned for use
between 120 and 150MHz. The pre-amplifier is suitable for
the 144-148MHz Amateur Band, and also suitable for weather
satellite reception on 137MHz. The pre-amplifier uses a low
cost BF998R MesFET that has very good characteristics on
the VHF and UHF bands. Devices like the ATF54143 were
considered but they are generally unstable on 144MHz, and
require the use of SMD components and additional circuitry
for biasing. The pre-amplifier is essentially a tuned input
BF998R MesFET, with a wideband 50ohm matching
transformer on the output. The pre-amplifier is best mounted
close to the antenna and incorporates RF changeover Relays
and power supply decoupling so that power can be fed via the
coaxial cable to power the pre-amplifier. The design is simple
to tune, and does not have any instability problems due to the
wideband output matching circuit.
AMPLIFIER DESCRIPTION: Refer to the circuit diagram. The
input filter consisting of a 2-10pF trimmer and L1, is a series
tuned resonant circuit that helps to reduce the 3dB bandwidth
of the amplifier to around 5MHz. This helps with overload
from signals outside the 144MHz band, especially strong Ham
50 and 430MHz transmissions. L1 connects to the 50ohm
tapping point on L2 and with another 2-10pF trimmer in
parallel forms the main input tuned circuit for the amplifier.
The noise figure is determined by the matching and the tuning
of the input filter trimmer capacitors. Back to back 1N5711
diodes, are used on both the input and output of the amplifier
to bypass any stray RF from destroying the MesFET when the
pre-amplifier is in TX mode. The BF998R is biased for 10mA
with 4 volts on Gate 2. The output impedance is matched to
50ohms using a high frequency F29 material ferrite balun
transformer. A 6dB attenuator on the output of the reduces
the gain to around 16dB and also helps with 50ohm matching
and RF protection.
RF RELAY SWITCHING: The Pre-amplifier has an RF
sensing circuit to ensure that the amplifier is bypassed in
Transmit mode. In Receive mode, the Relays are switched on
so that any loss of voltage to the amplifier drops the relays out
into bypass Transmit mode. Transmit RF is sensed via a 22k
resistor ( R1 ), and rectified by two 1N5711 diodes. The DC
voltage produced switches the BC547 transistor on, which
discharges the 10uF capacitor and pulls the 2N7000 Fet’s
gate input low. The Fet’s drain voltage goes high releasing
the relays into TX mode. When going back to Receive mode,
the 10uF capacitor discharges slowly to allow for SSB
operation inbetween voice peaks chattering the relays. The
relays however are best switched with DC from the
Transceiver, or from a Transmit sequencer with the RF
sensing being used as a safety circuit only. For manual DC
switching, the +12vdc supply to the pre-amplifier is controlled
by switching +12vdc to the pre-amplifier in RX mode, and dis-
connecting the power in TX mode. This can either be done
by feeding a separate +12vdc DC feed cable up to the pre-
amplifier, or by using the RF decoupling circuit L4 on the PC
board, and using the coaxial cable to feed +12vdc to the pre-
amplifier..
POWER SUPPLY: Refer to the circuit diagram. The
preamplifier uses a 78L08 regulator to provide the primary
voltage for the BF998R MesFET. Power supply filtering
capacitors are used to lower the regulator noise and decouple
RF from entering the power supply voltage rails.
CONSTRUCTION:
1. The PCB supplied is a professionally made plated through
hole board to make construction easier. It comes as a set of
two boards that can be broken apart easily, and filed flat to
clean up the boards edges Plated through earth holes are
shown as dark colored pads on the PCB overlay diagram.
Earth connections do not have to be soldered on both sides of
.COM.AU 2M VHF PRE-AMPLIFIER Rev4
Minikits
®
Copyright © Mini-Kits www.minikits.com.au Revised 29/12/2014

the board, only the bottom side. To assist construction
especially winding and mounting the coils, please refer to the
pictures on the Kits webpage.
www.minikits.com.au/eme157.htm
2. The first part of construction is to snap the two circuit
boards apart and cut away the break offs and file the edges
clean. The two board will be soldered together once all the
onboard components have been fitted.
3. Next install the small EME180 PC board and BF998R on
the bottom side of the board as shown in the PCB overlay
diagram. It may be easier to solder the small PC board to
the main EME157 board first before soldering the BF998R.
One lead on the BF998R is fatter and this is the source
connection, ( S ). Next tack solder one lead of the BF998R
to the small board, and check that you have the MesFET the
correct way around before completely soldering into place.
4. Fit the two 1N5711 schottky diodes as shown on the bot-
tom PCB overlay diagram. This a modification to the original
design to help protect the BF998R from damage. The diodes
will have to be fitted like SMD components with one end of
each diodes lead soldered directly to the strip-line on the
board. The other end of each diode can be mounted through
the holes in the PCB like a conventional components, and
flush cut.
5. Next you can start soldering the Resistors, Capacitors, and
remaining Diodes to the board. Make sure that you check the
correct orientation for the Diodes and Electrolytic Capacitors
before soldering in place.
6. Fit the 78L08 Regulator, BC547 Transistor, and 2N7000
FET to the board noting that the polarity of these components
are correct.
7. Next wind coil L2. For ( 144MHz the coil is 9 Turns of
0.9mm TCW around a 5mm drill bit and space the coils length
to 15mm long ) Refer to the picture on the web site listed
in the parts list for the correct way to wind and space L2.
The wire needs to be wound around the drill bit the
correct way so that it will fit the board. Fit the coil to the
PC board and sit the bottom of the coil 2mm above the
board and then solder into place.
8. Next wind coil L1. For ( 144MHz the coil is 16 turns of
0.3mm ECW wound 270 degrees around the brown T37-0
Toroid ). Once again refer to the web site pictures to make
sure you wind it around the core correctly. Cut the ends
of the wire short enough so that they can be connected to
the hole in the board and also to L2. For ( 144MHz L1 is
connected to the 3rd turn from the ground end of L2 ).
9. Next wind the BN29-1050 2 hole Balun core L3. For
( 144MHz wind 2 turns of 0.3mm ECW through the core A to
Bthen make a 15mm loop and twist the loop together for a
tap, and then wind a further 1.5 turns B to C ). One turn is
when the wire passes through one hole of the 2 hole
Balun, and then around through the second hole.
Passing through one hole is only a half a turn. Refer to
the web site pictures on how this is mounted to the PC board.
It can be a bit tricky and you need to remember which end of
the wire has the 2 turns to the tapping point for connection A
the BF998R Drain output connection.
10. Next wind the coil L4. For ( 144MHz the coil is 20 turns of
0.4mm ECW wound 240 degrees around the yellow T50-6
Toroid ). Once again refer to the webpage picture to make
sure that you wind it around the core correctly. Cut the
ends of the wire long enough so that they can be easily
connected through the holes in the board.
11. It is suggested that the Relays only be mounted after
the two PCB’s are soldered together, and the BNC sock-
ets are fitted in section 12. below.
12. The Preamplifier is designed to use the supplied sub PC
board to mount two BNC bulkhead connectors. This makes it
easy to use in conjunction with the optional GME mast head
amplifier enclosure. Simply tack solder the sub board to the
edge of the main board, and check the alignment, and make
sure that it fits into the masthead enclosure correctly. Don’t
fully solder until you have checked that the BNC
connectors can be fitted and the nuts done up without
fouling on the main board. Recheck the whole Preamp
assembly in the box before soldering the boards fully
together on both sides of the main board.
13. Fit the BNC sockets to the sub PCB, and do them up
tightly to avoid them loosening over time. Solder 0.7mm TCW
from the board connections to the sockets. Other connectors
should not be used as the diameter of the connectors may not
fit the GME masthead enclosure. If TNC connectors are avail-
able then these may be able to be used if they don’t foul on
the enclosure.
14. Cables greater than 6.5mm diameter will not fit through
the masthead enclosure, so cables like LMR240 are highly
recommended for low loss short runs. It is suggested that the
pre-amplifier be mounted close to the antenna feed point, and
a short length of LMR240 type cable be used to connect to the
antenna. On the output of the pre-amplifier a length of
LMR240UF ( ultra flex ) can be used to route around antenna
rotators to connect to the low loss feed line to the Radio room.
15. Mount the two Relays to the board. Make sure that you
flow the solder well as the connections need to be able to
handle high RF current in Transmit mode.
Copyright © Mini-Kits www.minikits.com.au Revised 29/12/2014
2M VHF PRE-AMPLIFIER EME157B2 Rev4

DRAWN
DATE
PROJECT
FILE
MINI-KITS
27-3-2013
2M PREAMP
EME157B2 VER4.SKF
2M PREAMPLIFIER
C2
2-10pF
L2
L3
BF998R
1nF
100k 1nF
1nF
100k 47R
0.1uF
78L08
REGULATOR
1N4148
RELAYS
BC547
2x 1N5711
1nF
1nF
R1
SELECT
10uF10uF
RL1
RL2
+10 to +15vdc
1nF
680K
2N7000
47k
150R
10uF
L1
L2 9 Turns 0.9mm TCW on a 5mm dia drill bit spaced 15mm long
L1 16 Turns 0.3mm ECW on a T37-0 Core 270 degrees
2x 1N5711
1nF
22k
ANTENNA
TO RADIO
L3 3.5 Turns taped 1.5 Turns from cold end 0.3mm ECW on a BN29-1050 Balun Core
C1
2-10pF
L4
T50-6
20 Turns
L4 20 Turns 0.4mm ECW Wound on a T50-6 Core
0.1uF
BN29-1050
T37-0
COPYRIGHT 2013
2T
1.5T
3T
6T
39R
150R 150R
G1
G2 D
S
2x 1N5711
COPYRIGHT MINIKITS

16. Finally when you are happy with it all, All the inductors
wound on the Toroid and Balun cores can be held in place
using some nail varnish. Once they have dried, they can then
be secured to the PCB with a small amount of non acidic
silicone, or hot melt glue. L4 can be secured to Relay RL2 the
same way. A piece of 10mm high, high density foam can be
glued onto the top of the right side relay, so that when the
masthead enclosure lid is shut, it holds the amplifier PCB
firmly in place.
TESTING and ALIGNMENT
1. Connect a +12 to +13.8vdc power supply to the pre-
amplifier and check that the relays engage. There is some
delay the first time power is applied due to the charging
of the delay capacitor. Power consumption should not be
much more that 100mA @ 12vdc in RX mode.
2. Alignment is straight forward, although some form of signal
source or VHF signal generator is an enormous help. Set the
two trimmer capacitors to half mesh.
3. Connect a receiver and suitable 50ohm dummy load or
antenna to the preamplifier, and tune it to the frequency band
that is to be used. All noise figure adjustments are best
adjusted on an FM signal. Set both trimmers so that they are
approximately half mesh. Using a signal generator or a stable
FM signal, adjust trimmer C2 for maximum gain, and C1 for
best signal to noise ratio, ( maximum quieting on a FM
receiver ). Reduce the FM signal level until more noise is
heard, and readjust the trimmers once again for best signal to
noise ratio.
Check the operation of the pre-amplifier when going to TX
mode. Connect the pre-amplifier to a suitable dummy load or
antenna that can handle at least the power output of the
Transceiver that you are using. Connect the Transceiver to
the preamp output, and Press the PTT to check that the
Relays drop out bypassing the pre-amplifier. On removal of
the PTT, the Relays should chick back on for RX mode with a
small delay.
APPLICATION NOTES:
1. The Pre-amplifier can be mounted in a suitable enclosure
for outdoor use. Mini-Kits supplies the plastic GME Kingray
masthead mount boxes that are suitable for mounting at the
Antenna. These last for years and are a quality design that
effectively seals the inside from water and moisture. If you
want a shielded enclosure, then the GME box can be sprayed
with Nickel spray, or use a suitable dicast weather proof en-
closure. The Nickel spray may provide some further protec-
tion from strong out of band signals that could enter the plastic
enclosure.
2. The pre-amplifier can either be powered via a DC power
cable connected directly to the board, or through the coaxial
cable. The easiest solution is to power the pre-amplifier using
a DC cable connected directly to the board, and use the on-
board RF sensing to switch the preamplifier. RF sensing is an
easy solution for switching the preamplifier using FM, but it is
much better to DC switch it, especially with modes like SSB
that can cause the relays to drop out during long pauses in
transmissions.
3. To power the pre-amplifier via the coaxial cable, a Bias
Tee is required to feed DC power into the cable. Some Trans-
ceiver like the Icom IC275 IC820/821, and IC910 already have
an internal Bias Tee and pre-amplifier sequencing built in.
These Transceivers are ideal for use with this pre-amplifier,
and output +12vdc from the antenna socket in RX mode when
the Preamp switch is turned on. They also have a TX delay
built in that is similar to the function of a sequencer, to further
protect pre-amplifiers by allowing time for the relays to drop
out for TX bypass mode. The recommendation for Transceiv-
ers without this built in, is to use a suitable VHF Bias Tee like
the Mini-Kits EME168 to control the switching, and feed the
power up the coaxial cable.
4. As mentioned above, the pre-amplifier is best switched
using a sequenced Bias Tee, or Transceiver with this built in.
If a sequenced Bias Tee is used, then the 10uF capacitor
connected to the 150 ohm resistor can be removed from the
circuit, to provide faster switching from TX back to RX modes.
The RF sensing should not be disconnected, as it does add
some further protection to the pre-amplifier, even when a se-
quencer is used.
5. The maximum power recommended is 100 Watts, and
is due to the Isolation of the Relays and the 1N5711 pro-
tection diode power handling capacity. The RF switching
requires a minimum of around 1 watt to switch the relays, and
this can be adjusted by changing the supplied 22k resistor R1.
The 22k was selected for 5 to 100 Watts input. For reliable
switching at lower power levels between 1 and 15 watts use a
2k2 resistor.
6. No adjustments are required to the Inductors as they have
been tested on prototypes using a Network Analyser and
Noise figure Meter for best performance. Inductors L1 and L2
have been optimized for a 5MHz bandwidth, and input
matching for a low noise figure. Inductor L3 has been
optimized for 50 ohms matching at 144 to 147MHz on the
output of the preamp. L4 has been optimized for the lowest
loss of RF power when in TX mode.
OPTIONS:
1. A 6dB attenuator is fitted to the output of the pre-amplifier
Copyright © Mini-Kits www.minikits.com.au Revised 29/12/2014
2M VHF PRE-AMPLIFIER EME157B2 Rev4

PARTS LIST
RESISTORS
1 x 39R 1/4 Watt MF Resistor
1 x 47R 1/4 Watt MF Resistor
3 x 150R 1/4 Watt MF Resistor
1 x 22k 1/4 Watt MF Resistor ( R1 Select )
1 x 47k 1/4 Watt MF Resistor
2 x 100k 1/4 Watt MF Resistor
1 x 680k 1/4 Watt MF Resistor
CAPACITORS
7 x 1nF Monolithic Capacitor 5mm X7R 100v
2 x 0.1uF Monolithic Capacitor 5mm X7R 100v
3 x 10uF ELC10GA35 Electrolytic 2mm Capacitor
2 x 2-10pF Trimmer Capacitor ( Yellow 144MHz )
SEMICONDUCTORS
1 x 1N4148 Diode ( Orange Black band )
6 x 1N5711 High Speed Diode ( Blue Black band )
1 x 78L08 Regulator 100mA TO92
1 x BC547 NPN Transistor TO92
1 x 2N7000 FET General Purpose
1 x BF998R Dual Gate MesFET
1 x PC Board EME180 ( to suit BF998R )
MISCELLANEOUS
1 x PC Board EME157B Set of 2 Boards
1 x Instructions EME157B6
1 x 0.7mm TCW 10cm Length ( BNC Connectors )
1 x 0.9mm TCW 35cm Length ( L2 )
1 x 0.3mm ECW 1.0 Metre Length, ( 30cm L1, 15cm L3 )
1 x 0.4mm ECW 40cm Length ( L4 )
1 x T37-0 Toroid ( Tan Colour For L1 )
1 x T50-6 Toroid ( Yellow Colour For L4 )
1 x BN29-1050 2 Hole Neosid F29 Balun Core L3
2 x Relays JW1FSN-DC12V ( Panasonic )
OPTIONAL
1 x ENCL19 GME Kingray Masthead amplifier Box
2 x BNS01 BNC Bulkhead mount sockets.
FOR PRODUCT SUPPORT
www.minikits.com.au/eme157.htm
2M VHF PRE-AMPLIFIER EME157B2 Rev4
to mainly reduce the gain to a more suitable level of around
16dB which seems to be a good level. This can be changed
to suit your application, but should be a minimum of 3dB to
help protect the pre-amplifier from RF when in TX mode. If
the Transceiver that you are using has an RF attenuator, then
It is recommended that this be turned on to reduce the re-
ceiver gain back to a suitable level when used with the pre-
amplifier. This will help with receiver overload from strong
signals, and give a better gain distribution while still getting the
low noise benefit of the pre-amplifier.
2. If your Transceiver does not have a preamp switch that can
feed DC power out the antenna socket, then the Mini-Kits
EME168 Bias Tee Kit can be used. Please see the webpage.
www.minikits.com.au/eme168.htm
Copyright © Mini-Kits www.minikits.com.au Revised 29/12/2014