|
EME157B2
KIT CONSTRUCTORS ALERT
There
appears to be a problem with the last batch of PC boards that
were made. The board should be checked thoroughly for any short
circuits to ground on the 12 volt input to the board before construction.
Some problems where a pad has been shorted to ground has been
found under the 680k resistor, BC547 transistor, & also the
plated through hole near the 2N7000 Fet. If you have a short then
use a sharp scalpel to carefully cut the short.
L4
has been changed to 4.5 Turns of 0.3mm ECW on the BN43-202 core.
This is to reduce the RF losses on the Trans mitt through path.
EME157B6
KIT CONSTRUCTORS ALERT
There
appears to be a problem with the last batch of PC boards that
were made. The board should be checked thoroughly for any short
circuits to ground on the 12 volt input to the board before construction.
Some problems where a pad has been shorted to ground has been
found under the 680k resistor, BC547 transistor, & also the
plated through hole near the 2N7000 Fet. If you have a short then
use a sharp scalpel to carefully cut the short.
L4
has been changed to 3.5 Turns of 0.3mm ECW on the BN43-202 core.
This is to reduce the RF losses on the Trans mitt through path.
CONSTRUCTION
OF THE EME157 PREAMPLIFIER KITS
|
The Image to the left shows
how the resistors, capacitors & diodes are soldered
to the board. Components only have to be soldered on the
bottom side of the board as the holes are plated through
|
The
above Images show how the coils are wound for the 2M 144MHz version
of the Kit. Take note of the winding direction of L1 & L2
especially so that they fit the board correctly. On the 2M version
the end on L1 is soldered to turn 3 on L2. However this was found
to not be all that critical in tests on a noise figure meter.
The
6M version is similar except for L1 & L2 which are slightly
different. L1 uses a larger T50-10 Toroid with more turns, &
L2 has more turns & is larger in diameter & length.
On the 6M version the end of L1 is soldered
to turn 4 on L2.
 |
This Image shows the completed
2M board before fitting the Sub PC board & Relays |
 |
 |
These
Pictures show how the Sub PC board is aligned to the main
board & tack soldered into place. After you are sure that
you have it aligned correctly, then solder it on both sides
to the main board. |
 |
 |
|
Above chart shows the measured
results of a prototype on a HP8970B Noise Figure Meter.
6M
Preamp in TX mode through path Return Loss Measured
on a Network Analyzer
|
2M
Preamp in TX mode through path Return Loss Measured
on a Network Analyzer
|
KIT
FAULTS & MODIFICATIONS EME157B2 KIT
1/
There can be various faults with this Kit which are mainly to
do with construction. On one Kit we could not get the RX/TX switching
circuit working. We found a 62ohm leakage from the gate of the
2N7000 fet to ground. We removed all components on that junction
except the 680kohm resistor & still measured 62ohms to ground.
We then removed the 680k & the 62ohm leakage disappeared.
We can only conclude that it could have been due to something
conductive on the board so we cleaned the board thoroughly &
reinstalled the components. There
appears to be a problem with the last batch of PC boards that
were made. The board should be checked thoroughly for any short
circuits to ground on the 12 volt input to the board before construction.
Some problems where a pad has been shorted to ground has been
found under the 680k resistor, BC547 transistor, & also the
plated through hole near the 2N7000 Fet. If you have a short then
use a sharp scalpel to carefully cut the short. The
RF sensing circuit can be tested by the small 1 to 2 second delay
of the Relays engaging when the power is first applied to the
Preamp.
2/
On later kits we have been adding a 6dB attenuator on the output
of the preamplifier before the relay to reduce the gain &
add more protection to the BF988 & 1N5711 diodes. Some have
complained of blowing the diodes & Fet when using up to 100
Watts on FM. The RF sensing circuit should not be used alone for
high power, & a separate control voltage to the preamp should
be used.
3/
Inter mod problems don't seem to be an issue with this Kit &
most problems can be directed to the receivers design. I recently
have been using the preamp on 2M SSB with local & DX signals
up to 60dB over S9 with sporadic E openings only some 10kHz away
without any problems. I use an IC275H which are a rather reasonable
receiver. Don't expect your TS2000, IC706 or 7000 etc to perform
as good as the older receivers. I recommend turning the radios
preamp switch off on late model Radios if you are going to use
the EME157 2M preamp. On the IC820/821 the attenuator switch can
be turned on when using the preamplifier at the Antenna.
4/
Some Radios are prone to producing a spike on the RF output when
going into transmitt mode. This can be due to the ALC in the Radio
not acting fast enough. This is a sure way to blowing the preamps
diodes & BF988. You will have to hard switch the preamp as
the RF sensing will not be able to cope with this high level spike.
If you have problems with the preamp being damaged then check
on the Internet for any problems that may be associated with your
Radios model.
5/
In construction notes before March 2009, the notes mention winding
a 70cm length of 0.3mm ECW onto the BN43-202 core L4. This is
incorrect & should be 4 to 5 turns of 0.3mm ECW. The extra
turns causes loss on 144MHz in TX mode which is excessive. The
approximate inductance of L4 when wound correctly is around 50uH.
| 6/
To power the preamplifier from a separate 12 volt connection
to the board, fit a 1nF or larger feed through capacitor in
the hole that is drilled on the sub PC board. Re-arrange the
windings on L4 to 5 turns as shown in the picture to the right.
Solder one end of L4 to the board & the other end of L4
to the feed through capacitor. Connect +Ve 12 volts to the
feed through capacitor, & -Ve 0 volts connection to the
circuit board ground. This Mod also stops any 12 volts from
being fed back down the coaxial cable to the Radio. |
 |
KIT
FAULTS & MODIFICATIONS EME157B6 KIT
1/
In construction notes before March 2009, the notes mention winding
a 70cm length of 0.3mm ECW onto the BN43-202 core L4. This is
incorrect & should be 3.5 turns of 0.3mm ECW. The extra turns
causes loss on 50MHz in TX mode which is excessive. The approximate
inductance of L4 when wound correctly is around 25uH.
2/
Also refer to the above notes for the 2M Kit version.
 |
Modification to the first batch of EME157
circuit boards to fit a 6dB attenuator after the 1N5711
diodes to reduce the gain to around 16dB, & add extra
RF protection to the 1N5711 diodes & BF988 MesFET. |
The
above picture shows the completed 2M Preamplifier ready to mount
in a masthead box.
|
HOME | E-MAIL
|
| NEWS
| PRODUCTS | TECHNICAL
| DOWNLOAD | ORDERING
|
This
and all subsequent pages copyright 2001 - 2010 by Mini-Kits
All rights reserved
|
Tuesday
3rd August 10
