Status - QRV
1/10/2007
1/10/2007
This is a description of my
new 24.048GHz system. The old 24.192GHz system was retired in
2000 after many years of reliable service and lots of good DX worked,
including the then UK distance record and
the first QSOs with ON.
My ideal was to build the new transverter using all-coax construction. I soon realised this was not going to be very practical, since the Millitech 2.5W amplifier uses waveguide input and output. Also, the 3 section RF filter (necessary with a 144MHz IF) and DB6NT transverter were also waveguide parts. The solution was to use waveguide 20 (WG42) to coax transitions where necessary. Fig 1 shows the block schematic of the transverter.
Fig 1 shows that there are 4 coax/WG transitions in the transverter plus the one in the transverter unit.
The sequencer is a simple double relay type as described by GM3SEK. These sequencers are uncritical and are used extensively in my various transverters. In practice it is normally only necessary to sequence the PA and the antenna relay. This simple design does this very adequately and it is most reassuring to hear the double click from the 2 relays!
The sequencer board also provides a stable 28V for the two APC3.5 connector (26.5GHz) relays.
A high stability 124.500MHz DF9LN OCXO (using a good ol' two stage bipolar Butler 5th overtone crystal oscillator!) is kept permanently running in the shack and supplies 0dBm input to the masthead mounted transverter. Inside the masthead unit the DB6NT oscillator multiplies the 124.500MHz to 11952MHz at approximately +16dBm. This then feeds the DB6NT transverter unit which in turn feeds the 3 stage cavity filter (3 stages ensures that any LO feed though and image are sufficiently suppressed, since the MMTech amplifier still has a great deal of gain at 23904MHz (LO) and 23760MHz (image). The transverter, filter and one of the coax/WG transitions are the only parts remaining from the original 24192MHz transverter.
I bought the MMTech power amplifier from Paul Drexler at the 2002 MUD, held in Enfield, Conn. USA. It was one of the most powerful units he had available at that time.
Since it requires less than -20dBm input for full (saturated) output at 24048MHz and the DB6NT transverter provides approximately -5dBm output, it is necessary to use a coax attenuator on the amplifier input to protect the amplifier from overdriving and possible destruction. In practice the 20dB attenuator shown in the diagram is actually a 10dB and a 3dB in tandem, since the coax/WG transition and the short length of coax provide significant extra loss at 24GHz. 20db will provide complete protection against overdriving, but output will be less that 2W.
A 12V 2A regulator supplies the PA and is switched by the sequencer.
I measure 2.3W output at the transverter output waveguide flange.
The DB6NT preamplifier measures 1.8dB nf and 23dB gain. When connected in the system with coax, waveguide, adapters and relay into the DB6NT transverter, the system noise figure is 2.2dB. I regard this as very acceptable for terrestrial, but probably a little high for 24GHz EME! A second preamplifier (already built and available) will reduce the nf to below 2dB. I don't think this is worth the effort at the moment. 1dB would be nice!
The antenna is an NEC (Pasolink) 30cm prime focus dish with Cassegrain feed. This dish was originally used on my 47GHz system.
Playing with dish feeds for 24GHz I was disappointed by the performance of the 60cm Sky analogue dish with dual band feed. The disappointment came more from mechanical stability than from gain, although even this didn't meet my expectations. Whilst a few more dB gain would undoubtedly be available, the sharpness of the beam and the backlash on the rotator system persuaded me that a 60cm dish was not practical for my home 24GHz system. Whilst pondering this I looked at some of my other, smaller, dishes, and my eyes fell on the NEC 30cm dish. On close examination I discovered that the 'Antenna 2' conical horn had dimensions more akin to what I would expect on 24GHz than on 50GHz. As the Pasolink antenna feed system was designed to be progressively enhanced it appeared that maybe the intermediate 'Antenna 2' may have been designed for 18 - 23GHz use? Running the HDL-ANT programme told me that the horn waveguide input might overmode on 24GHz (yes, overmode!), but it was marginal. But, nevertheless it would have exactly the right beam width to illuminate the sub reflector. I fashioned a simple WG20 adapter from an old square to round WG20 adapter section and epoxied it into the mounting hole in the NEC 'Antenna 2' horn. The match showed about 8dB return loss, which would later be improved by matching screws.
When I set up my antenna test range the NEC 30cm dish was only about 2dB down on the 60cm Sky dish and 1dB up on my old 25cm Procom dish with Procom feed. This also confirmed my suspicion that the Sky dish was not performing as it should.
The NEC antenna integrates well with the transverter to form a rugged, one-piece 24GHz system, in contrast to the Sky dish based system.
Prior to 2000 I had worked 7 grid squares, 3 DXCC countries (G, ON, PA0) and ODX of 267km on 24GHz. Time to see if I can better that!
Page added 26/12/2006
Updated 24/01/2007
Mk 2 24GHz transverter with
'modified' 50GHz NEC Pasolink 30cm Cassegrain dish feed
My ideal was to build the new transverter using all-coax construction. I soon realised this was not going to be very practical, since the Millitech 2.5W amplifier uses waveguide input and output. Also, the 3 section RF filter (necessary with a 144MHz IF) and DB6NT transverter were also waveguide parts. The solution was to use waveguide 20 (WG42) to coax transitions where necessary. Fig 1 shows the block schematic of the transverter.
Fig 1 Block diagram of the 24G
transverter.
Fig 1 shows that there are 4 coax/WG transitions in the transverter plus the one in the transverter unit.
Fig 2 inside of the 24GHz
transverter
The sequencer is a simple double relay type as described by GM3SEK. These sequencers are uncritical and are used extensively in my various transverters. In practice it is normally only necessary to sequence the PA and the antenna relay. This simple design does this very adequately and it is most reassuring to hear the double click from the 2 relays!
The sequencer board also provides a stable 28V for the two APC3.5 connector (26.5GHz) relays.
A high stability 124.500MHz DF9LN OCXO (using a good ol' two stage bipolar Butler 5th overtone crystal oscillator!) is kept permanently running in the shack and supplies 0dBm input to the masthead mounted transverter. Inside the masthead unit the DB6NT oscillator multiplies the 124.500MHz to 11952MHz at approximately +16dBm. This then feeds the DB6NT transverter unit which in turn feeds the 3 stage cavity filter (3 stages ensures that any LO feed though and image are sufficiently suppressed, since the MMTech amplifier still has a great deal of gain at 23904MHz (LO) and 23760MHz (image). The transverter, filter and one of the coax/WG transitions are the only parts remaining from the original 24192MHz transverter.
I bought the MMTech power amplifier from Paul Drexler at the 2002 MUD, held in Enfield, Conn. USA. It was one of the most powerful units he had available at that time.
Since it requires less than -20dBm input for full (saturated) output at 24048MHz and the DB6NT transverter provides approximately -5dBm output, it is necessary to use a coax attenuator on the amplifier input to protect the amplifier from overdriving and possible destruction. In practice the 20dB attenuator shown in the diagram is actually a 10dB and a 3dB in tandem, since the coax/WG transition and the short length of coax provide significant extra loss at 24GHz. 20db will provide complete protection against overdriving, but output will be less that 2W.
A 12V 2A regulator supplies the PA and is switched by the sequencer.
I measure 2.3W output at the transverter output waveguide flange.
The DB6NT preamplifier measures 1.8dB nf and 23dB gain. When connected in the system with coax, waveguide, adapters and relay into the DB6NT transverter, the system noise figure is 2.2dB. I regard this as very acceptable for terrestrial, but probably a little high for 24GHz EME! A second preamplifier (already built and available) will reduce the nf to below 2dB. I don't think this is worth the effort at the moment. 1dB would be nice!
The antenna is an NEC (Pasolink) 30cm prime focus dish with Cassegrain feed. This dish was originally used on my 47GHz system.
Playing with dish feeds for 24GHz I was disappointed by the performance of the 60cm Sky analogue dish with dual band feed. The disappointment came more from mechanical stability than from gain, although even this didn't meet my expectations. Whilst a few more dB gain would undoubtedly be available, the sharpness of the beam and the backlash on the rotator system persuaded me that a 60cm dish was not practical for my home 24GHz system. Whilst pondering this I looked at some of my other, smaller, dishes, and my eyes fell on the NEC 30cm dish. On close examination I discovered that the 'Antenna 2' conical horn had dimensions more akin to what I would expect on 24GHz than on 50GHz. As the Pasolink antenna feed system was designed to be progressively enhanced it appeared that maybe the intermediate 'Antenna 2' may have been designed for 18 - 23GHz use? Running the HDL-ANT programme told me that the horn waveguide input might overmode on 24GHz (yes, overmode!), but it was marginal. But, nevertheless it would have exactly the right beam width to illuminate the sub reflector. I fashioned a simple WG20 adapter from an old square to round WG20 adapter section and epoxied it into the mounting hole in the NEC 'Antenna 2' horn. The match showed about 8dB return loss, which would later be improved by matching screws.
When I set up my antenna test range the NEC 30cm dish was only about 2dB down on the 60cm Sky dish and 1dB up on my old 25cm Procom dish with Procom feed. This also confirmed my suspicion that the Sky dish was not performing as it should.
The NEC antenna integrates well with the transverter to form a rugged, one-piece 24GHz system, in contrast to the Sky dish based system.
Prior to 2000 I had worked 7 grid squares, 3 DXCC countries (G, ON, PA0) and ODX of 267km on 24GHz. Time to see if I can better that!
Page added 26/12/2006
Updated 24/01/2007