6cm ATV activity isn't usually comparable with the traffic presents into
24cm and 13cm bands, in fact this band is often and unjustified snobbed to
the 3cm band. For this reason it is hard or not frequent to found projects
treat home-made realizations into 5.7GHz band.
I think the first and most important step to open activity into a new band
is to dispose of a valid RX system.
The following project of 5.7GHz Down-Converter offers a very good
performances with a NF<1dB and a Gc @ 40dB. I adopted an external
Synthetized LO (derived from 1.2GHz Exciter) so the locked frequency
stability it's sum-up on the others good features. This project is a good
start to open 6cm band!
DESCRIPTION OF THE CIRCUIT
Two HEMT amplifiers are utilized in the front-end stage to obtain a Noise
Figure less than 1dB (0.5dB@10GHz on data sheet) with an RF Gain @ 30dB.
Follow a 2 pole Interdigited Band Pass Filter. Its scattering data is
reported into follows graph obtained with the software Sonnet© r8.51.
A similar filter, but tuned on 4.6GHz (fig.2), is placed on the IN-LO and
it's working with an HEMT amplifier to run out the 3td harmonic from the
1553.375MHz original signal on the SMA connector. The 4600MHz RF signal
obtained is sended to the Mixer for the IF conversion on 1.1GHz.
The utilized active Mixer is an IAM81008 (Pdf data sheet) from HP and it's
offers a Gc=-2dB at 5.7GHz with an IF on the 1150MHz range.
The MMIC INA10386 brings a Gain of 20dB on the final IF signal.
ELECTRIC SCHEMATIC
All power supply, also for the external LO, are derived from the IF
connector connected to the SAT Rx (It@300mA) so we have a single cable
wired to the Rx !
The Bias for the Gates of the HEMT it's generated from the i.c. 7660 and
it's regulated by the trimmers P1 and P2 to obtain the indicated Vds
values like on the schematic.
The pad EXT_VCC_IN is useful to connect an external power supply during
the instrumental test of circuit. In this manner the IF-OUT connector have
only the RF component without Vcc.
PRINTED CIRCUIT BOARD
The Pcb is realized on a teflon board type RT5870-30 (Er=2.33 and
Thickness=0.762mm). We can utilize the equivalent MY3 product.
PCB layout (.pdf) is available in Download:
IK8UIF-57CONV.PDF
IMPORTANT! To obtain the correct dimension of PCB un-check all regulations
into Acrobat_Reader Print menu.
Layout of components:
PCB is drilled with a 0.7mm point and we must manually flaring the holes on
GND side using a 4mm drill point. Not flaring the holes DESTINED to GND!
The components in BLUE color are assembled on the GND-SIDE of PCB.
In the same side wiring the jumpers between pads J1-J1, J2-J2 and J3-J3.
For the GND VIA connections (indicated with GREEN pads) I utilize a little
COPPER CYLINDER ROLL (abt 0.7mm diameter) derived from the shield of H100
cable.
Insert the cylinder into any GND hole and solder it on GND and component
sides. With a cutter remove any overhanging parts.
This method warranty a good GND connection necessary for the frequency in
use and for a correct working of Down-Converter.
You must use a tin-plate (or also pcb derived) enclosure with internal
dimensions of 98x58x22mm. An RF-Absorber must be glued on the internal
up cover to prevent reflecting "wave guide" paths causing self-oscillations.
The three rf connectors employed are SMA-F type and are soldered on the
external sides of the tin-plate box.
THE LO MODULE
The required LO signal can starts from any RF oscillator on 1533,375MHz
(x3=4600,125MHz) with an RF power in the range between 0dBm ÷ 8dBm.
Here's the down-conversion frequency table:
Fin (MHz) -- IF (MHz)
5650÷5850 --> 1050÷1250
I use a LO module derived from an Exciter 1.2GHz modified to 1500MHz range.
In this manner the LO is PLL locked so the IF frequency is surely
indicated on your SAT RX display !...
The adoption of a locked LO make possible the utilize of this
Down-Converter also in not-ATV applications, perhaps with a 2nd conversion
but in consideration of the total noise-phase produced.
The modify of Exciter 1.2GHz and the relative pic's software it's will be
soon available in my Projects Page.
Good Atv in 6cm!
73s de Ik8UIF Alberto
de Ik8UIF 