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EME221 Series Preamplifier Kits

  • EME221-70CM pre-amplifier

Please Note: that all information including pictures on this web page are copyright to Mini-Kits and must not be used on any other web site, or reproduced in any publication.

EME221-70CM KIT Description:

The EME221-70CM is a High performance masthead mount Receiver Pre-amplifier that is specifically designed for the 70cm 430 to 450MHz band. The Pre-amplifier has an adjustable 20 to 29dB gain, and can be used to optimize gain distribution for coaxial cable losses and the total gain of the receiver system. The design uses the Mini-Circuits PGA-103 that has a very high dynamic range and ultra low 0.38dB noise figure. The input circuit consists of a tunable T type filter that can be tuned to optimize the noise figure to less than 1dB while giving high rejection of signals below 200MHz. The output of the PGA-103 is filtered with a low pass filter giving high rejection of signals above 500MHz, and is then further amplified by a low noise Avago MGA82563 PHEMT MMIC. The design incorporates high isolation RF changeover Relays to bypass the pre-amplifier when not required, or when RF power from a transmitter is applied to the antenna. An on board bias tee ( DC power injector ), allows the pre-amplifier to be antenna mounted and powered via the coaxial cable. The Preamplifier is able to handle 50 Watts ( +47dBm ) CW, when unsequenced, or up to 100 Watts ( +50dBm ) PEP when sequenced. Due to the high cost of the HF353 Relays, the EME221-70CM product is to be replaced with a lower cost EME237-70CM product around August 2021.

EME221-23CM KIT Description:

The EME221-23CM is a High performance masthead mount Receiver Pre-amplifier that is specifically designed for the 23cm 1240 to 1300MHz band. The Pre-amplifier has an adjustable 7 to 21dB gain, and can be used to optimize gain distribution for coaxial cable losses and the total gain of the receiver system. The design uses the Mini-Circuits PGA-103 that has a very high dynamic range and ultra low 0.38dB noise figure. The input circuit is untuned broadband to decrease losses for a noise figure under 1.5dB, ( Typically < 1.1dB ) including Relay and circuit losses. Thee output of the PGA-103 is filtered with a 1200MHz high pass filter giving high rejection of signals below 1000MHz, and is then further amplified by a low noise Avago MGA82563 PHEMT MMIC. The design incorporates high isolation RF changeover Relays to bypass the pre-amplifier when not required, or when RF power from a transmitter is applied to the antenna. An on board bias tee ( DC power injector ), allows the pre-amplifier to be antenna mounted and powered via the coaxial cable. The TX bypass has a loss of around 0.8dB which limits the maximum RF power to 25Watts ( +44dBm ) CW, when unsequenced, or up to 50 Watts ( +47dBm ) PEP when sequenced. Tests so far have not shown RF power loss as radiant heat when tested with a thermal imaging camera, so further testing is required at higher power levels to determine if a higher RF power can be used.

The PC board is designed to suit a low cost GME mast head enclosure which makes installation easy and provides high protection of the circuitry from weather.

Kit Constructors Alert:

1/ Do Not construct this Kit unless you are very experienced with surface mount construction, and only if you have a quality soldering station and around 0.5mm 60/40 Tin Lead solder. Any mistakes can be very costly to repair as we saw with a recent customer repair that had a number of faults mainly due to soldering. The solder used was a lead free type that contained a flux that seemed to be conductive and it got underneath many of the components including the relays. No cleaning of the board with isopropanol seemed to clean the flux from the board. The repair included removing and replacing the relays that also seemed to have a high resistance through the contacts one being 4.7ohms and the other a bit over 100ohms. It is unclear if this was due to flux or the relays being damaged by excessive heat. A number of capacitors also had to be replaced due to excessive RF loss. After the repair the preamp was tested and the relays intermittently dropped out and the fault was traced to more flux under the 2N7002 MosFET. When finally tested, the preamplifier had an instability that was traced to more flux under the PGA-103 that then also had to be replaced. The repairs in the end cost more than 3 hours labour compared to around 1.5 hours for us to build one from scratch.

2/ A very small number of customers have reported HF353 Relays that have measured open circuit in TX bypass mode. The Relays can be easily damaged due to excessive heat when soldered, or some built products may have been damaged by shock in the postal system. When constructing, it is suggested that a soldering iron with a hot setting is used so that it will quickly heat and flow solder between each pin and the board reducing the time which could cause internal damage. Mini-Kits will not replace Relays supplied in Kits as they are factory tested in sealed packaging.

EME221-ALL PREAMP KITS

1/ There have been some issues reported with low return loss causing RF power loss in TX bypass mode. This has in most cases been traced to constructors deciding to not use the recommended RF connectors directly on the board, and using coaxial cable that is poorly terminated to external connectors. This can also be caused after cleaning the board with isopropyl alcohol that has not fully dried and remains between the connectors and the board. The board should be heated using a hair drier to help with evaporation of cleaning fluids, and left for some time to dry fully before testing. Some issues may also be overheating of the Relays when soldering them to the board.

EME221-70CM Kit Notes:

The pictures below are a final revision so should be carefully followed in construction. Be careful when fabricating and fitting L4 as it needs to be done correctly to achieve the lowest transmit power loss and high return loss. On a prototype I was not very careful when fitting the QF0.085 cable under the board between points A and B, so this created a short from the braid to one on the PCB pads which was not very obvious so check this carefully. Slight filing of the two slots at the top of the board is required to fit the GME masthead enclosure. This was unfortunate as the PCB manufacturer made a slight mistake with the board route out. The board should be fully cleaned with Isopropyl Alcohol and thoroughly dried using a hair drier before testing. Through loss tests may not be achievable if there is Isopropyl still under the connectors and relays. The performance tests below are as measured on a number of built products and were nearly all identical. BUY THIS PRODUCT

  • EME221-70cm Top View
    Top view of the EME221-70CM showing the recommended TNC connectors
  • EME221-70cm Bottom View
    Bottom view of the EME221-70CM showing the short coax connection for TX bypass
  • EME221-70CM-L1
    Fitting of the input inductor L1, and the approximate position on the trimmer capacitor C2
  • EME221-70CM-L4
    How L4 is fitted and spaced for a high return loss in TX mode.
  • EME221-70CM cable connection
    How the QF0.085 cable is connected to the board providing clearance between the circuit board pad and the outer braid to avoid shorting.
  • EME221-70CM Resistor Mod
    How R11 is fitted in series with D4 for the power supply modification. See Kit changes and updates.
EME221-70CM Kit Tests:

  • EME221-70CM Input Filter
    EME221-70CM S21 Gain Test Showing T input filter response
  • EME221-70CM Wide Response
    EME221-70CM S21 Gain Test Wide Span
  • EME221-70CM TX Bypass
    EME221-70CM TX Bypass showing S11 Return loss
EME221-23CM Kit Notes:

The pictures below are a final revision so should be carefully followed in construction. Be careful when fabricating and fitting L4 as it needs to be done correctly to achieve the lowest transmit power loss and high return loss. On a prototype I was not very careful when fitting the QF0.085 cable under the board between points A and B, so this created a short from the braid to one on the PCB pads which was not very obvious so check this carefully. Slight filing of the two slots at the top of the board is required to fit the GME masthead enclosure. This was unfortunate as the PCB manufacturer made a slight mistake with the board route out. The board should be fully cleaned with Isopropyl Alcohol and thoroughly dried using a hair drier before testing. Through loss tests may not be achievable if there is Isopropyl still under the connectors and relays. The performance tests below are as measured on a number of built products and were nearly all identical. BUY THIS PRODUCT

  • EME221-23cm Top View
    Top view of the EME221-23CM showing the recommended TNC connectors
  • EME221-23cm Bottom View
    Bottom view of the EME221-23CM showing the short coax connection for TX bypass
  • EME221-23CM-L4
    How L4 is fitted to the board for lowest loss and >20dB return loss in TX mode
  • EME221-23CM cable connection
    How the QF0.085 cable is connected to the board providing clearance between the circuit board pad and the outer braid to avoid shorting.
  • EME221-23CM Resistor Mod
    How R11 is fitted in series with D4 for the power supply modification. See Kit changes and updates.
EME221-23CM Kit Tests:

  • EME221-23CM Frequency Response
    EME221-23CM S21 Maximum Gain Test Showing The filter response
  • EME221-23CM Minimum Gain
    EME221-23CM S21 Minimum Gain Test
  • EME220-23CM-Wide-S21
    EME221-23CM S21 Maximum Gain Wide Span
  • EME220-23CM-TX-Bypass-S21
    EME221-23CM TX Bypass showing S21 loss
  • EME220-23CM-TX-Bypass-S11
    EME221-23CM TX Bypass showing S11 Return Loss which should be greater than 20dB
Mounting into a Die cast Enclosure:

The Hammond 1590S or 1590SFL die cast enclosure is ideal for mounting the preamplifier module for in shack use. The enclosure allows either the TNC or BNC type R/Angle PC board mount connectors to be easily used for minimum loss. The board sits on M3 x 8mm high brass spacers mounted to the enclosure with M3 x 6mm countersunk screws.

  • EME221 1590S Top View
    The EME221 board mounted in a Hammond 1590S Enclosure
  • EME221 1590S Side View
    The EME221 board mounted in a Hammond 1590S Enclosure
  • 1590S-Countersunk-Holes
    3mm holes drilled to suit the M3x6mm Countersunk screws
  • 1590S-BNC-Holes
    Holes drilled to suit the diameter of the BNC connectors
  • 1590S-DC-Connector
    Hole drilled to 6mm to suit the 2.1mm DC socket connector
  • 1590S-RF-Connectors
    Fitting of RF connectors through the enclosure
Mounting Procedure:

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, M12, and 1.4 inch drill bits, scriber, metal punch, and a hammer.

  • Place an unpopulated EME221 PC board into the enclosure and mark the four mounting holes using a fine felt tip pen. Using a punch and hammed mark the centre of the mounting holes for drilling. Drill out the four holes starting with a 1.5mm drill bit followed by a 3mm bit. Counter sink the holes on the bottom of the enclosure to suit M3 x 6mm countersunk screws.

  • Mount the PC board into the enclosure on M3x8mm brass spacers using 4x M3x6 countersunk screws and 4x M3x6 Phillips head screws. Mark the positions for the BNC connectors using a felt tip pen, and then remove the PC board.

  • Mark and drill two 12.5mm holes in the die cast enclosure as shown in the picture above to suit the BNC connectors, and a 8mm hole to suit the 2.1mm DC connector.

  • Mount the completed PC board pre-amplifier module into the enclosure and fit the BNC connectors to the enclosure. The board when fitted to the enclosure should have a tight fit around the BNC connectors not requiring any fastening of the connectors to the enclosure.

  • Mount the 2.1mm DC connector to the enclosure rotating it to the position as shown in the pictures. Carefully fully tighten the nut using a small spanner or wrench.

  • Connect the 2.1mm DC connector to the +ve connection on the terminal connector for the power using a small length of insulated hookup wire.

  • Finally tune the pre-amplifier as per the Kit construction notes for the best noise figure.

Mounting into a Masthead Enclosure:

The GME Masthead enclosure will accept coaxial cables up to around 8mm in diameter. Therefore larger cables like CNT®-400 and RG8/213 cannot be used. Larger cables would also place too much strain on the TNC sockets on the pre-amplifier board. Some customers have tried to use TNC male to N type female adapters to connect to the main feedlines, but the extra length will not fit inside the enclosure. To connect the Antenna feed line to the pre-amplifier, and pre-amplifier output to the main feed line, we recommend the use of CNT®240 ( 240 Type ) cable with crimped TNC connectors. CNT®240 is double shielded and has losses similar to RG213 cable, but has a much smaller 6.5mm diameter. Use the website search box and search for ( 240 type ) to see all the available cable and connectors.

  • GME Enclosure Mounting
    The EME221 board mounted in a GME Masthead Enclosure
  • GME Enclosure Locking Tab
    The Enclosure has a locking Tab that holds the board firmly
  • Masthead Installation 1
    Picture shows the masthead amplifier mounted directly on the support pole under the 70cm yagi antenna. The TNC male connectors are fully sealed with heatshrink.
  • Coaxial Feedline Installation
    A short 0.5m long CNT-240 patch cable with a TNC male to N type female is used on the output of the Preamp to connect to the main CNT-400 feedline.
CONNECTION TO A TRANSCEIVER:

1/ Mini-Kits cannot be expected to take responsibility to make this product work on your Transceiver, we can only give guidance on how best to use this product. Using this product with high power FM or SSB modes does have the risk of damaging the Pre-amplifier if the transceiver switches from RX to TX modes faster than the pre-amplifiers relays. Some protection is built into the pre-amplifier circuit including a RF sensing circuit and Limiter diode protection, but high RF levels into the pre-amplifier before it has fully switched from RX to TX mode can damage the pre amp. Some Transceivers are prone to producing a spike on the RF output when going into transmit mode. This can be due to the ALC in the Radio not acting fast enough. This is where a sequencer circuit is useful to sequence the switching of RF amplifiers and pre-amplifiers so that the relays etc have enough time to switch RX to TX mode before RF power is applied. The Relay isolation that has been tested on the EME237-70CM Kit should easily allow up to 100Watts PEP( +50dBm ) of RF to be used.

2/ Transceivers including the ICOM IC-475, IC-1275, IC-820/821, IC-910, IC-9100, and IC-9700, have a pre amp switch with delay sequencing built in, so they are all able to directly power a pre-amplifier through the antennas coaxial cable connection so require no external bias tee.

3. For other Transceivers including the TS2000, TS2000X and IC706 series without inbuilt preamplifier switching and bias tee, the preamplifier can be powered either by running a DC power cable directly to the pre-amp board, or by feeding it up the coaxial cable. For FM operation, the onboard RF sensing circuitry can be simply used, but for SSB it is much better to use an external bias tee to power through the coaxial cable. Many Transceivers have access to a +12 volt TX connection on the accessories socket on the rear. This can be used to control the bias tee switching the +12vdc to the pre amp in RX mode, and disconnecting it in TX mode. At this time the RF sensing circuit should still be used on the pre-amp as a fail safe, as there is no delay sequencing built into the bias tee.

Refer to the basic application blocks below for the TS2000, and page 104 in the TS2000 owners manual.

Kit Changes and Updates:

EME221-70CM

1/ August 2020, the EME221-70CM product has been retired and replaced with the EME237-70CM.

2/ With Kits after November 2019, the MGA82563 has been replaced with a PSA-0012, and R2 has been changed from a 24 to 10R to suit.

3/ The power supply circuit has been modified to reduce the dissipation from the +5v 78M05 Regulator. A 22 ohm 2 Watt MOS resistor is now fitted in series with Diode D4 to reduce the voltage to the input of the regulator. If you are powering the preamp to the PWR connector, then it is suggested to fit the resistor in series with D3 instead of D4. Please see the construction picture for how the components are mounted.

4/ There have been some issues reported with low return loss causing RF power loss in TX bypass mode. This has in most cases been traced to constructors deciding to not use the recommended RF connectors directly on the board, and using coaxial cable that is poorly terminated to external connectors. This can also be caused after cleaning the board with isopropyl alcohol that has not fully dried and remains between the connectors and the board. The board should be heated using a hair drier to help with evaporation of cleaning fluids, and left for some time to dry fully before testing. Some issues may also be poor soldering of the relays to the board, and the solder not being flowed into the boards plated holes fully. In rare cases a relay could have been damaged in transit especially on a built product. This can be tested using a multimeter for continuity.

5/ There have been reports of failure of the PGA-103 due to lightning damage. It is suggested that the preamplifier power is turned off when there are storms to prevent any damage.

6/ The wire hoop L1 should be 10.5mm from the PCB to the very top of the wire loop not 10mm as shown on some early circuit diagrams.

7/ Instability type noise that randomly lifts the S meter when in SSB mode was traced to a damaged PGA-103. It was suspected that it may have been damaged by excessive heat when soldering.

8/ No transmit RF through the preamp can be due to one of the relays connections not being fully soldered. Refer again to the Kits notes on the importance of fully soldering the relays connections. Also refer to 3/ above.

EME221-23CM

1/ With Kits after November 2019, the MGA82563 has been replaced with a PSA-0012, and R2 has been changed from a 24 to 10R to suit.

2/ The power supply circuit has been modified to reduce the dissipation from the +5v 78M05 Regulator. A 22 ohm 2 Watt MOS resistor is now fitted in series with Diode D4 to reduce the voltage to the input of the regulator. If you are powering the preamp to the PWR connector, then it is suggested to fit the resistor in series with D3 instead of D4. Please see the construction picture for how the components are mounted.

3/ There have been some issues reported with low return loss causing RF power loss in TX bypass mode. This has in most cases been traced to constructors deciding to not use the recommended RF connectors directly on the board, and using coaxial cable that is poorly terminated to external connectors. This can also be caused after cleaning the board with isopropyl alcohol that has not fully dried and remains between the connectors and the board. The board should be heated using a hair drier to help with evaporation of cleaning fluids, and left for some time to dry fully before testing. Some issues may also be poor soldering of the relays to the board, and the solder not being flowed into the boards plated holes fully. In rare cases a relay could have been damaged in transit especially on a built product. This can be tested using a multimeter for continuity.

4/ Higher than expected losses through the pre-amplifier in TX mode can be due to circuit losses caused by the 0.3pF capacitor C20, or the incorrect fabrication of L4. In some cases replacing this capacitor has fixed the problem but it could also be flux under the capacitor that may have caused the extra loss.

5/ Issues with receive gain or not producing the correct frequency response can sometimes be traced to the Mini-Circuits LFCN-1200 filter. There have been issues with these filters at times being faulty.  This could possibly be due to damage when soldering to the board. Also check that you have soldered all connections to the board including the earth connections.