EME221 Series Preamplifier Kits

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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.

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:

EME221-70CM

1/ Do Not construct this Kit unless you are very experienced with surface mount construction, and only if you have a quality soldering iron and 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 clear 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.

1/ 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.

EME221-23CM

EME221-70CM Kit Notes:

The pictures below are a final revision so should be carefully followed in construction. Be carefully when fabricating and winding of the L1 and L4 inductors as they will affect the performance if they are not accurate. L4 especially needs to be accurately fabricated as it also cancels the capacitance on the Transmit bypass path to give a very low 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 performance tests below are as measured on two final built products and were nearly identical. BUY THIS PRODUCT

EME221-70CM Top View
Top view of the EME221-70CM

The picture shows the basic EME221-70CM Kit with Molex TNC connectors that have been used for high reliability and low loss.

EME221-70CM Top View
Top view of the EME221-70CM

The picture shows how the QF0.085 cable is connected between the A and B connections for the Transmit 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 lowest transmit power loss, ( High return loss )
EME221-70CM-CAB
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 Performance Tests:

EME221-70CM-TFIL-S21
EME221-70CM S21 Gain Test Showing T input filter response
EME221-70CM-W-S21
EME221-70CM S21 Gain Test Wide Span
EME220-6M-S21
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 carefully when fabricating L4 especially needs to be accurately fabricated as it also cancels the capacitance on the Transmit bypass path to give a very low 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 performance tests below are as measured on two final built products and were nearly identical. BUY THIS PRODUCT

EME221-23CM Top View
Top view of the EME221-23CM

The picture shows the basic EME221-23CM Kit with Molex TNC connectors that have been used for high reliability and low loss.

EME221-23CM Top View
Top view of the EME221-23CM

The picture shows how the QF0.085 cable is connected between the A and B connections for the Transmit bypass.

EME221-23CM-L4A
How L4 is fitted close to the board for lowest transmit power loss, ( High return loss )
EME221-23CM-L4B
How L4 is fitted and spaced for lowest transmit power loss, ( High return loss )
EME221-70CM-CAB
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 Performance Tests:

EME221-23CM-Max-S21
EME221-23CM S21 Maximum Gain Setting
EME221-23CM-Min-S21
EME221-23CM S21 Minimum Gain Setting
EME221-23CM-Wide-S21
EME221-23CM S21 Maximum Gain Wide Span
EME221-23CM-TX-Bypass-S21
EME221-23CM TX Bypass showing S21 loss
EME221-23CM-TX-Bypass-S11
EME221-23CM TX Bypass showing S11 Return Loss

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.

1590S-ENC-1
The EME221 board mounted in a Hammond 1590S Enclosure
1590S-ENC-2
The EME221 board mounted in a Hammond 1590S Enclosure
1590S-Countersunk-Holes
3mm holes drilled to suit the M3x6mm Countsersunk screws
1590S-BNC-Holes
Holes drilled to 12mm to suit the BNC connectors
1590S-DC-Connector
Hole drilled to 6mm to suit the 2.1mm DC socket
1590S-BNC-Connectors
Fitting of BNC connectors and connection to the board

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 12mm 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 tighted 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 cables up to around 8mm in diameter. Therefore larger cables like RG8/213 cannot be used. Larger cables would also place too much strain on the TNC sockets on the pre-amplifier board. 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 6mm diameter. Use the website search box and search for 240 series cable and connectors.

GME Enclosure 1
The EME221 board mounted in a GME Masthead Enclosure
EME221-ENC-1
The Enclosure has a locking Tab that holds the board firmly

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 high Relay isolation that has been tested on the EME221-70CM Kit should easily allow up to 100Watts PEP( +50dBm ) of RF to be used as long as the Pre-amplifier is sequenced.

2/ Powering the pre-amplifier with +10 to 15vdc can be either by running a DC power cable direct to the pre-amp board, or by feeding it up the coaxial cable. Transceivers like the ICOM IC475, IC820/821, IC910, and IC9100 have a pre amp switch with delay sequencing, and are able to directly power the pre-amp through the coaxial cable and require no additional circuitry. Popular transceivers like the TS2000, TS2000X and IC706 series do not have internal bias tee circuitry to send +12vdc out via the rear antenna to power external pre amps. So additional circuitry will be required to interface the transmit switching from the transceiver to power the pre amp in RX mode.

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

3/ The Mini-Kits Bias Tee or DC Power Injector allows the pre-amplifier power to be easily switched via 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. The EME166 Sequencer can be used to control the sequencing of pre-amps and high power RF amplifiers with a transceiver.

Kit Changes and Repairs:

EME221-70CM

1/ There have been recent reports of failure of the PGA-103 due to lightning damage. It is suggested that a HSMP4820 limiter Diode is connected on the input of C1 to ground to help protect the PGA-103. It will be difficult to install a diode but it can be done. The diode may slightly increase the noise figure but it is unlikely that the difference is audible.

2/ 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.

3/ 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.

4/ Excessive loss through the relays was traced to the relays that were probably damaged due to excessive heat when soldering.

EME221-23CM

1/ Higher than expected losses through the preamplifier in TX mode can be due to circuit losses caused by the 0.3pF capacitor C20. 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.