EME173-Rev2 Preamplifier Kits
 EME173-2M Preamplifier Kit
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The EME173 PC board was updated in January 2015 to improve the input matching circuit for a lower noise figure. The board was designed to suit the construction of receive only preamplifiers for the 30 to 500MHz bands. All Kits use the low cost BF998 MesFET from NXP that has a low noise figure and were designed for television tuners. The output of the BF998 is matched to 50ohms using a tapped transformer ensuring stable operation. The preamplifiers can all be adapted for frequencies outside the ranges specified for each product, by simply changing the turns on the input inductor. The upper range of the EME173-70CM Kit however is around 500MHz maximum.
1/ November 2015, Built products are now fitted with a 2.1mm DC socket and 1N4007 diode for the external power connection. The DC connector makes it much easier to connect DC power and the diode provides reverse polarity protection to the circuitry. See the pictures below for the change to this product.
The Preamplifier has been designed to be easy to construct, and can be centre frequency tuned for use between 45 and 65MHz, and is suitable for the 50-54MHz Amateur Band. A low cost BF998 MesFET has been used as it has very good characteristics on the VHF to UHF bands. The BF998 was specifically designed for television tuners, and has a low 0.7dB NF at 50MHz along with high cross modulation performance. The BF998 incorporates integrated gate input protection diodes to help prevent damage to the device from static. The Preamplifier design is essentially a tuned input MesFET, with a wide band 50ohm matching transformer on the output. The Preamplifier however can also be used on a 75ohm antenna, or coaxial cable systems. BUY THIS PRODUCT
Top view of the EME173-6M The picture shows the basic EME173-6M Kit with optional SMA connectors. The red toroidal inductor allows the amplifier to be powered via the coaxial cable as a masthead amplifier. | 
BF998 mounted to the PC board
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Shows the BF988 marking |
Fitting of the input inductor L1 showing the wire tap.
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How to position the output matching transformer L2. | 
Fitting of inductor L3 for DC power via the coaxial cable. | 
How to solder coaxial cable to the board when connectors are not required. |
The Preamplifier has been designed to be easy to construct, and can be centre frequency tuned for use between 115 and 180MHz, and is suitable for the 144-148MHz Amateur Band. A low cost BF998 MesFET has been used as it has very good characteristics on the VHF to UHF bands. The BF998 was specifically designed for television tuners, and has a low 0.7dB NF at 145MHz along with high cross modulation performance. The BF998 incorporates integrated gate input protection diodes to help prevent damage to the device from static. The Preamplifier design is essentially a tuned input MesFET, with a wide band 50ohm matching transformer on the output. The Preamplifier however can also be used on a 75ohm antenna, or coaxial cable systems. BUY THIS PRODUCT
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Top view of the EME173-2M The picture shows the basic EME173-2M Kit with optional SMA connectors. The yellow toroidal inductor allows the amplifier to be powered via the coaxial cable as a masthead amplifier. |
BF998 mounted to the PC board
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Shows the BF988 marking |
Fitting of the input inductor L1 showing the wire tap.
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How to position the output matching transformer L2. | 
Fitting of inductor L3 for DC power via the coaxial cable. |
How to solder coaxial cable to the board when connectors are not required. |
The Preamplifier has been designed to be easy to construct, and can be centre frequency tuned for use between 350 and 500MHz, and is suitable for the 430-450MHz Amateur Band. A low cost BF998 MesFET has been used as it has very good characteristics on the VHF to UHF bands. The BF998 was specifically designed for television tuners, and has a low noise 1dB NF at 435MHz along with high cross modulation performance. The BF998 incorporates integrated gate input protection diodes to help prevent damage to the device from static. The Preamplifier design is essentially a tuned input MesFET, with a wide band 50ohm matching transformer on the output. The Preamplifier however can also be used on a 75ohm antenna, or coaxial cable systems. BUY THIS PRODUCT
Top view of the EME173-70CM
The picture shows the basic EME173-70CM Kit with optional SMA connectors. The yellow toroidal inductor allows the amplifier to be powered via the coaxial cable as a masthead amplifier. |
BF998 mounted to the PC board
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Shows the BF988 marking |
Fitting of the input inductor L1 showing the wire tap.
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How to position the output matching transformer L2. | 
Fitting of inductor L3 for DC power via the coaxial cable. |
How to solder coaxial cable to the board when connectors are not required. |
EME173-6M Preamplifier Gain and Bandwidth Test S21
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EME173-6M Preamplifier output return loss S22
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EME173-2M Preamplifier Gain and Bandwidth Test S21
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EME173-2M Preamplifier output return loss S22
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EME173-70CM Preamplifier Gain and Bandwidth Test S21
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EME173-70CM Preamplifier output return loss S22 |
This is for advanced constructors that have experience and access to a workshop with metal working tools. The basic tool requirements are a drill press, Vice, M1.5, M3, M6, and 1.4 inch drill bits, scriber, metal punch, and a hammer.
Top view of the EME173-70CM
The picture shows the basic EME173-70CM Kit mounted into a Hammond 1590A Enclosure. | 
Alignment for drilling the 1/4" holes for the SMA connectors. Also shows the use of a nickel plated M6 shake proof washer
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Drilling guide for the Hammond 1590A enclosure |
How the SMA42 connector and extra nut are used to fit the enclosure
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How to solder the1N4007 Diode from the DC connector to the board. |
There can be some variations with connectors, and mounting hardware thicknesses that may require some experimentation when mounting boards into enclosures. Recently some SMA panel mount connectors may require additional washers due to the female thread not going all the way to the mounting flange. Many of the shake proof washers that are being supplied with SMA connectors are very flimsy and easily deform when tightening, so one picture above shows the use of a M6 shake proof washer that was used to securely hold the SMA connector to the enclosure.
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Solder an extended SMA female, ( SMA39 ) to the input of the PC board making sure that it is at right angles to the board. Take your time here to make sure that the SMA connectors on both the input and output of the preamp are straight in both planes.
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The SMA12 male PCB connector will need modifying as it will not easily slide onto the RF output connection board. Modify the connector by breaking two diagonal tabs of the bottom of the flange to allow the connector to fit flat onto the top of the board. Solder the connector to the top of the PCB making sure that it is at right angles to the board. See the picture above to see how it is then soldered to the bottom ground plane of the PCB.
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Mark and drill the two 1/4 inch holes in the die cast enclosure as shown in the picture above. If you are fitting the optional 2.1mm DC connector, then also mark and drill a 8mm hole to suit.
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Near the input of the PC board cut the corners away using a nibbling tool so that they clear the corners of the enclosure. Refer to the picture above on how this is done.
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Fit a extended SMA female to female bulkhead mount ( SMA42 ) through one end of the enclosure and screw a nut and washer on only by couple threads to allow enough clearance to then get the preamp board into the enclosure. Refer to the picture above on how two nuts and a washer are used to take up the clearance on the outside of the box. Some experimentation with the washer may be required to fit the SMA42 adaptor. Sometimes Mini-Kits mounts the washer inside the enclosure, or if its too tight a fit it is then mounted on the outside.
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Slide the preamp board into the enclosure and pass the extended input SMA connector through the hole in the enclosure, and lightly screw on the SMA nut and washer to hold it into place. In many cases a M5 nickel steel shake proof washer maybe used to secure the connector better.
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Lightly tightened up the output SMA male to the SMA bulkhead adaptor.
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Finally carefully tighten the input SMA nut using a suitable SMA spanner. Finally the nuts on the output SMA bulkhead adaptor can be tightened ensuring that there is not excessive stress placed on the board and connectors.
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Fit the 2.1mm DC connector to the enclosure and rotate it and tighten the nut as shown in the picture above. Fit the 1N4007 diode as shown in the picture to protect the preamp from reverse polarity.
A simple Bias Tee Kit is now available that is suitable for powering the 6m to 23cm preamplifiers via a coaxial cable. The SWR return losses have been tested to be better than -20dB with losses less than 0.2dB. These products have been designed for receive only use not for transmitting through. BUY THIS PRODUCT
Top view of the EME195B Module board
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EME195U-ENC Version
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1/ Slight drop of gain when CT2 is adjusted with an insulated screwdriver,, replace the 1nF SMD capacitor on Gate 2 of the MosFET.