Use and Modification of the Ionica 9cm (3400MHz) Receive Converter
The Ionica receive converters can be used on the amateur band with no modification, however improvement with small mods are worthwile.
Mixer is MCL SYM2190M. Lo level required is +14dBm (1 dB pad fitted on ip)
Converter gain 49dB, ( temperature compensated and manually adjustable) nf <3.3dB IF range 941.5 to 957.8MHz. Original input frequency range 3425 to 3441MHz
Recent information has identified the pin out of the 9way D type connector. Note the +ve supply regulator to the GaAs fets does not become active unless -12v is present.
|4||Temperature OP (LM335)|
|9||Noise diode switch|
The IF frequency of the converter is centred on 947.5 MHz. To use any other IF, requires the IF filter to be Bypassed. The IF gain stages work OK at 1296. Front end filtering is insufficient for image rejection with 144 IF and probably 432 IF
|In initial tests the filter and all IF gain stages were by bypassed to lower the overall gain. The mixer op (still via the attenuator) was connected to the IF output socket directly with thin coax||
Modified front end as originally tested
Shown to the left is a close up of the part of the front end where the Pin diode switching for the noise source is. I have removed the Pin diode that is connected to the main RF stripline ( by the screw) and cut the tracks to the other diode and its bias arrangement next to the coupling capacitor. Rx noisefigure improves noticably.
No retuning is required for operation on 3400MHz
The IF filter (947MHz) and probably the gain stages will need to be bypassed if any amateur band IF is planned.
It has been suggested that the unit can be used as is, by providing a local oscillator at 814MHz. This is multiplied by 3 to give LO to the converter (2442MHz) This produces an IF of 958 MHz which the IF filter should pass OK. An external mixer can then be used with the 814 MHz local oscillator, to produce a second IF of 144 MHz. The approach has now been tested by G4BAO and is implemented on his website. (Link on the Pa use and mods page)
If a first IF is planned below 900MHz, it is likley that the image response of the converter will be poor. External filtering and an LNA would be a good idea in this case.
The front end of the Ionica receiver works well enough to be a viable receiver without a pre-amplifier, though a significantly better system noise performance is acheived with a good Low Noise Amplifier.