A simple way to convert a Storno CQM5662 to 1296 MHz.
General layout :
Receiver.
The injection signal for the mixer is taken from the CQM5662 RX-injection-chain, where C316 is connected to L306.
The frequency is approx. 425 MHz (439 MHz), which is doubled to approx. 850 MHz (879 MHz) in the new module,
and delivered to the new mixer.
Mixerinjection to 1. mixer can be chosen higher or lower than the signalfrequency.
Listen around the frequencies 418 MHz and 446 MHz with a receicer or scanner.
If You here strong signals from nearby transmitters in one of the frequencybands,
then use the other frequencyband as 1. IF.
I have chosen the 446 MHz band.
Transmitter.
Three ways are tested :
1 : Using the transmitter unchanged, but extended with a varactor multiplier.
2 : Original PA-section removed, and last driver in exciter changed to multiplier.
New drivers and PA build in the space, where the original PA had place.
3 : Original PA-section removed, and a new multiplier, driver and PA constructed
in the space, where the original PA had place.
Storno CQM5662S (synthesizer version) can be used as well, see frequencyplan below.
To get 25 kHz channel separation it is necessary to modify reference frequency and division ratio in synthesizer.
__________________________________________________________________________________________________________ Construction :
Receiver:
The new module containing RF amplifiers, mixer and frequency-doubler is placed,
where the tonemodule used to be.
My first handpainted 1296 MHz receiverconverter, constructed in 2005.
From left to right : BFR91A, MAR6, mixer BFR91A and doubler BFR96S.
Schematic and printboard of 2.RF (MAR6), mixer (BFR91A) and doubler (BFR96S) is shown below :
Doublesided board, bottom side unetched. Many through-connections to improve stability (wires soldered on both sides)
Populated print, all SMD, made by OZ2ZJ. (Solder the board to sides all the way round on both sides)
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To connect the RX-converter to CQM5662-RF-board, two methodes are tried.
If You do not cut off the PA-section, connections can be done by drilling small holes through the board, close to the relay,
and connecting RG174-coaxcables (teflon).Space under the board is very limited, so be carefull.
A few printconnections must be removed, using a sharp knife.
Copperstrip between relay and coil must be grounded to prevent unwanted signal feedthrough. NOTE : be carefull, when You remove the printboard from the chassis.
Screws and nut holding PA and driver transistors must be removed, or the transistors will break.
Output to frequency doubler can be connected via 100pF on componentside at L306/C316 as shown below.
Coaxcable is run as shown, and a small slot is made on edge of coverbox.
The simple way is to use a varactor-tripler.
There are several designs on the internet,
an example made by VK2TDM is described in Propagator October 2003 : Click here for more.
It works well, output 4-6 watt. (reduce the output from PA-stage to 6-8 watt)
I have tried several ways to triple and amplify the output from the exciter (approx 100 mW).
The complete PA-section and PA-section of the cover are cut off, see picture below:
One of many experiments shown below.
The PA transistor was a BFQ34 (not shown on picture), delivering nearly 1 watt.
Latest (2009) I tried a Mitsubishi RA18H1213G MOSFET module, see below.
From exciter output signal is coupled to a BFR96S tripler, then driver MAR SNA186 (not visible), and the RF-module.
It is very stable, output can be adjusted from zero to 15 watt, and no spurs and harmonics, see below.
Transmitting at full power for several minutes makes the radio very hot, so some sort of cooling is needed,
or reduced output must be used.
Despite the cost of the RF-module (60 Euro), I will work more on this method in near future.
Schematics ,boards and misc. info to the CQM5000-family can be found here :
My Circuit Library.
