2009-12-10
The first 10 pieces of this transverter we built on base "OZ KIT's by
permission of the supplier.Later we modified the PCB and the original design,
but we using lot of original ideas of the autor(OE9PMJ)The mechanics,the box and
the oulet is 100% our own design.
We don't sell KIT's look OZ2M if you need it.
The 70 MHz input signal passes through the input filter (L1, C1, C2) to the input amplifier (BF981) where the gain is approx. 25 dB. Then through the band pass filter (L2 - 4, C3 - 8) providing a suitable selectivity.
The balanced mixer MX1(SBL-1) mixes the 70 MHz signal down to 28 MHz loosing approx. 6 dB in the process. Next the signal is amplified approx. 10 dB in a low noise J-FET (J310). The band-pass filter (L7/8 and C11 - 14) increases the selectivity considerably. Undesired products are decoupled via R5 in the L5/C9 diplexing filter.
For better stability the oscillator chain is supplied with 9V from a 78L09 voltage regulator. The oscillator, another J310, oscillates on 42 MHz using a 14MHz crystal on 3rd overtone mode, series resonance. The 42 MHz signal is being amplified through Q6 to approx. 17 dBm/50 mW. In the following low-pass filter the harmonics are being attenuated. Then the signal is attenuated to approx. 7 dBm/5 mW through R14 - 18 which also provides impedance matching for the TX and RX mixers(SBL-1).With L17 you can set the crystal to correct 42.000MHz frequency.
The transmit mixer, MX2, only needs approx. -15 dBm/30 µW 28 MHz IF signal from the transceiver. A suitable level can be achieved by adjusting VR in the attenuator (R30, R31 and VR). The resulting 70 MHz TX signal is then filtered through a three-stage band-pass filter (L12 - 14/C 25 - 30) before being amplified in a BF981, and finally a BFR96TS to a level exceeding 100-150 mW. Through the final pi-filter (L16/C34 - C36) the TX signal reaches the output terminal.
The PTT circuit uses two BD136 for the RX/TX switching, TX when PTT is grounded. At the "DR4" terminal +12 V/1 A is available during TX. It is intended to switch the antenna relay and/or a PA. The circuit around the BC547 delays the TX key while activating the antenna relay immediately. This means that the TX output (70 OUT) is delayed approx. 100 ms after the antenna relay is activated. Consequently the antenna relay switches without any TX signal present.
The complete transverter is build on a 1,5 mm double sided glass-fibre epoxy PCB to be fitted into a standard metal sheet box measuring 148 x 74 x 30 (50) mm3. The component (upper) side of the PCB.
The RX/TX shift is done the way it is, due to the fact that some transceivers
only have a single transverter RF connector, common for the RX input and the TX
output. If you have separate connectors for RX and TX, the 28 MHz relay is not
needed.
42MHz xtal not easy to find we using here 14MHz xtal in 3rd overtone mode.
The L17 help to set the xtal frequency to 42.000MHz.
We don't using RF connectors on the box every signal connecting directly with RG174 coax cables.
If the TX-IF-signal source is not adjustable and the TX mixer is fed with the
proper levels, it is possible to introduce an adjustable TX output by changing
the gate 2 voltage on Q8 (BF982). This can be done fixed or adjustable by
connecting gate 2 to an external potentiometer in stead of R23.
This additional poti is on the front page and you can set the output pwr from 0
to the maximum..
| General |
Operational frequency span |
: : |
69.9,0 MHz - 71MHz 27,9MHz - 29 MHz |
| TX |
Output power |
: : : : |
>200 mW -15 dBm - 0 dBm/30 µW - 1 mW, adjustable 25dB -40dB >60 dB |
| RX |
Gain |
: : : : : : |
ca. 23 dB <2 dB 0 dBm/1 mW 7 dBm/5 mW 98 dB 94 dB |
Fig 1. RX front-end passband characteristics. TV channel 4 is attenuated by 12 dB and the FM-band beyond 68 dB.
Fig 2. TX third order intermodulation distortion at 22 dBm/159 mW PEP.
Fig 3. TX spurious at 21 dBm/125 mW. All spurious are more than -65 dBc.
| Resistor | Value |
| R1, R22 | 27 kΩ |
| R2 | 10 kΩ |
| R3, R14, R18 | 180 Ω |
| R4, R7, R25, R29 | 22 Ω |
| R5, R19 | 47 Ω |
| R6, R17 | 150 Ω |
| R8 | 8,2 kΩ |
| R9 | 2,2 kΩ |
| R10 | 1,2 Ω |
| R11 | 5,6 kΩ |
| R12 | 15 kΩ |
| R13, R26 | 1 kΩ |
| R15, R16, R24 | 39 Ω |
| R20 | 22 kΩ |
| R21 | 3,3 kΩ |
| R23 | 1,5 kΩ |
| R27 | 4,7 kΩ |
| R28 | 12 Ω |
| R30, R31 | 82 Ω |
| VR | 250 Ω |
All resistors are 0,25 W/0,4 W and metalfilm type.
| Capacitor | Value |
| C1, C7, C14, C24, C26, C32 | 120 pF |
| C2, C8, C28 | 27 pF |
| C3, C4, C30, C31 | 22 pF |
| C5, C6, C27, C29 | 1 pF |
| C9 | 270 pF |
| C10, C11, C25 | 33 pF |
| C12 | 3,3 pF |
| C13, C34, C35 | 39 pF |
| C15 | 100 nF, polyester, 2-raster |
| C16 | 1 µF, 16 V, electrolytic, axial |
| C17, C18 | 22 µF, 16 V, electrolytic, axial |
| C19, C21 | 82 pF |
| C20 | 150 pF |
| C22 | 10 pF |
| C23 | 47 pF |
| C33 | 1 nF |
| C36, C37 | 12 pF |
| C38-C59 | 10 nF |
All capacitors are 1 raster, 2,54 mm, ceramic types unless otherwise stated.
| Component | Description |
| D1, D2 | 5,6 V zener diode, 0,5 W |
| D3, D4 | 1N4004 or equivalent |
| D5, D5, D7 | 1N4148 or equivalent |
| IC1 | 78L09 |
| MX1, MX2 | SBL-2, or similar +7dBm |
| Q1, Q8 | BF981 or BF982 |
| Q2, Q7 | J310, U310 |
| Q3, Q4 | BD136, or similar PNP |
| Q5 | BC547 |
| Q6 | BFW93, BFW92 |
| Q9 | BFR96 or BFR96TS |
| Inductor | Description |
| DR1, DR2, DR3, DR4, DR5, DR6, DR8 | VK200, ~10 µH RF choke |
| DR7 | 15 µH RF choke |
| L1, L2, L3, L4, L12, L13, L14, L15 | Neosid 00 5231 03 |
| L6, L7, L8 | Neosid 00 5048 00 |
| L9, L10, L11 | Neosid 00 5049 00 |
| L5, L16 | Neosid 00 5061 00 |
| Component | Description |
| Ferrite beads | Mount on Q1 and Q8 drain |
| Crystal | 14 MHz, HC49/U |
| Metal sheet box | 148 x 74 x 30 (or 50) mm3. Schubert type. |
| Feed through capacitors | Three x 1 nF, solderable into a 3,2 mm hole |
| Metal sheets | Big on top side, small on bottom side |
| Relay | Omron G5V-2, 12 V N.C. |
The original 50 MHz design by OE9PMJ had two IF options: 28 or 144 MHz. A 144 MHz IF for the 70 MHz version would need an oscillator on 74 MHz! That is simply too close to 70 MHz to keep the oscillator signal out of the desired pass band and is outside the scope of this 70 MHz design. Thus 144 MHz IF is not an option! The prototype 6m version of this transverter I built in 1990 by OE9PMJ description.
by Bo, OZ2M, www.rudius.net/oz2m