10 GHz FLEX/DEMI-1500&144IF 2 Meter Transceiver

The purpose of this mash-up is to package the PCBs from a DEMI L144-28INT intermediate transverter and DEMI ApolLO synthesizer within the covers of a modified FLEX-1500 transceiver while retaining the ability to revert back to the original multiband FLEX-1500 configuration. My FLEX-1500 is used primarily as in IF transceiver. I've been looking to reduce the number of cables and boxes for my 10 GHz station configurations. When Down East Microwave Inc. (DEMI) announced a small form factor 2 meter intermediate transverter I just had to try and package it within my FLEX-1500.

FLEX-1500

DEMI L144-28INT

Dis-assembly of the FLEX-1500


Assembly of the "FLEX/DEMI-1500&144IF" Transceiver


Initial Results:

• High performance IF transceiver with up to 100 mW (linear) RF output on 2 meters. Note that my unit measures 180 mW output on 2 meters which is sufficient to drive my DB6NT 10 GHz transverter, 3 Watt DEMI amplifier and 8 Watt DEMI amplifier to full power output!
• Both the transceiver and transverter are locked to an external 10 MHz reference frequency.
• DC power consumption is reduced by the removal of the FLEX-1500 HF/6 band hardware.
• Simplified PTT control via common RF connector to external, microwave transverters.

DEMI L144-28INT kit Assembly Considerations:

• There are two semiconductor packages that I hadn't seen in a kit before. They are the SOT-89 PHA-1 monolithic amplifier and TTT167 SYM-18H mixer, both of which were a challenge to install on the PCB. Pre-tinning the PCB, precise component alignment and careful soldering are a must for the safe installation of these devices. DO NOT overheat these devices (like I did)!
•  Due to the PCB width and wire/component placement near the PCB edges, the +9V overflow wires need to be soldered directly to the voltage regulator pin rather than the designated PCB +9V plated-through holes that are too close to the PCB edge.
• Up to 3 relays are used depending on your configuration (1 for RF switching, 1 for IF switching and 1 for mode switching). All of them need to be mounted on the top, component side of the PCB; not the bottom as shown. This is to provide adequate clearance within the enclosure. Note that you'll need to change the RF and/or IF relay +12 VDC source from TXON to RXON if you locate these relays on the top side of the PCB.
• My output RF (144 MHz) configuration uses a single BNC connector for both TXRF and RXRF thereby eliminating an external relay. You can configure with two BNC connectors for separate TXRF and RXRF, if necessary.

DEMI VHF ApolLO Integration Considerations:

• VHF ApolLO Synthesizer 

•  VHF ApolLO Background, etc.

•   Mounting of the ApolLO within the Flex-1500 enclosure is a bit of a challenge. You need a clean 12 VDC power source, a clean 10 MHz signal source and a short 116 MHz signal distribution to the intermediate transverter LO input.

• I chose to sandwich the ApolLO PCB in between the Flex-1500 and DEMI-L144-28INT PCBs near the front panel for minimum LO cable length.
• The 116 MHz output is connected to the intermediate transverter just after the crystal oscillator output and before the LO amplifier that drives the mixer. The LO signal levels were approximately the same between the crystal oscillator and the ApolLO. 
• There is a provision for an optional LED that indicates "lock" but I chose not to use it.
• The 10 MHz reference frequency input is a separate BNC connector in addition to the Flex-1500 10 MHz reference frequency input BNC connector. No attempt was made to combine and/or re-power these within the enclosure as there is already enough RF floating around within the enclosure.

Packaging and Interconnection Considerations:

•  I chose to use a new enclosure so as to not modify the original FLEX-1500 enclosure and provide better access. The Hammond HM979-ND ($21.50 from Digi-Key) has the same dimensions but with a sliding bottom useful for mounting the DEMI L144-28INT PCB. You can use the original FLEX-1500 enclosure if you don't mind drilling additional mounting holes in the bottom or use a different intermediate mounting plate.
• A new rear panel was patterned from the FLEX-1500 back panel from brass plate stock (K&S Engineering 2" wide X 0.065" thick cut to 4.06" long). It also functions a a heat sink for the +5V regulator required for the FLEX-1500 PTRX PCB. The original FLEX-1500 back panel would have worked if I had used only a single, common IF output connector.
• Be careful to not reverse the Ground and +5V plugging into the bottom connector of the FLEX-1500 PTRX PCB. I'd recommend checking your connections with an ohm meter BEFORE power is applied! Remember that one side of the connector has 3 ground pins (away from the BNC connectors) and that there are two pins for +5V. Take a close look at this picture. +5VDC is the ONLY voltage that you need to apply to the PCB (NOT +12V)!
• I used a VHF ApolLO as the 116 MHz local oscillator so the analog oscillator components were not used. This did require a connector on the back panel for a 2nd 10 MHz reference frequency input (separate from the transceiver 10 MHz reference frequency input).
• Other than these items, all three of the PCBs fit inside the enclosure and the original FLEX-1500 front panel was reusable without any modification.
• More information on the FLEX-1500 can be obtained from the free service manual (available on request to FLEX-1500 owners).
• The overall weight was increased by 4 oz (0.11 kg)  from 1 lb 5 oz (0.61 kg) to a total of 1 lb 9 oz (0.72 kg).

Cooling Considerations: 

•  Use of the VHF ApolLO synthesized 116 MHz local oscillator eliminated all sources of frequency drift.

• However, in order to meet all three of the PCB component operating temperature limitations, additional cooling was needed. Note that the ApolLO synthesizer PCB may not lock up if its recommended temperature range is exceeded.

• A combination of air escape holes drilled into both sides of the enclosure and a bottom mounted, thin fan (2 1/4" x 2 1/4" x 3/8" thick) were added to force air through the enclosure thereby lowering the external case temperature down from 95'F to 80'F (with only 9 VDC applied to the fan for lower noise level).
• This change increased the effective height of the enclosure by 3/4 " to a total of 2 3/4".

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