The RadioJove kits are high quality radio kits designed, by Dick Flagg, especially for radio astronomy. The kits come with with metal boxes for the receivers and the bits required to make the phased-array dipole antennas. The only drawback with these kits is that, depending on the currency conversion and your budget, these kits aren't particularly cheap. If you already have some of the required equipment and money is your main constraint you might consider Ten-Tec 1056 radio kits, although they do require more tweaking to do useful astronomy.
We cannot provide full instructions for assembling the kits - but excellent documentation is available from the official Radio Jove website. Here we only discuss the steps that are necessary to make an interferometer out of two kits.
|If you plan on using the metal boxes that come with the Jove receivers, you will need to add a new RF connector to each box. On one box we'll use the connector to break the Local Oscillator (LO) signal out and on the other box it will bring the LO signal in. The picture below shows the back of Simple's first receiver... the new "LO Output" connector is evident.|
The first receiver is assembled according to the kit instructions. It's a good idea to connect the receiver to an antenna and test that it works correctly once you've completed it. This includes using the 20MHz crystal to calibrate the operating frequency.
Once you've assembled and tested the first kit, you can wire in the "LO Output" connector. This connector needs to be wired up to pin 7 of the NE602 (through a DC blocking capacitor). Connect the core of a short piece of coax to the track (on the underside of the Jove circuit board) which connects to pin 7 of the NE602. Connect the shield of the coax to any nearby ground track, such as that around the perimeter of the board.
|On the connector end of the coax, you can connect the coax shield to the chassis and the coax core to the connector core via a capacitor (say 10nF, since it is used as to block any DC voltage the value isn't critical). The image below shows what we're on about:|
In the interferometer configuration, the second receiver differs from the RadioJove design in that we disable the on-board Local Oscillator (LO). However it is probably best to fully assemble and test the receiver, as per the RadioJove instructions, before building your interferometer.
Having built and tested the second receiver, the modifications to inject a LO signal are pretty straight-forward. First you need to remove the capacitors C13 and C14. This disconnects the tuned circuit for the on-board LO from the NE602. The photo below shows "Simple" with C13 and C14 disconnected (notice we only bothered to desolder the NE602 side of the capacitors rather than remove them completely).
To drive the NE602 with an external LO we need to inject the LO signal onto pin 6. You should solder the core of a short piece of coax to the track (on the underside of the Jove circuit board) which connects to pin 6 of the NE602. Solder the shield of the coax to any convenient ground.
The other end of the coax needs to be wired to the new "LO Input" connector you installed in the metal box. Once again it is a good idea to run the signal through a DC blocking capacitor to ensure no DC voltage is applied to the NE602. The photo below shows the underside of Simple's second receiver.
Your second receiver is now ready to have an external LO injected. The external LO signal must be between 200-300mV peak-to-peak. If your LO amplifier runs off 12V then it's output is more likely to be around 10V peak-to-peak. Therefore before you connect the output of your LO amplifier to the "LO Input" of your second receiver you must attenuate it by 20-30dB! If you don't have an oscilloscope you may need to experiment with attenuator values.
You are now ready to test if your system. Set the receivers up in the proper
configuration, with the LO amp (and attenuators) between the "LO Output"
of your first receiver and the "LO Input" of your second receiver.
Connect some antennas and speakers and turn on the power, you should be able
to hear noise from both of the Jove receivers. As you tune past radio stations
you should hear pretty much the same output from both of the receivers - this
shows you have correctly injected the LO - your interferometer is ready for
first fringes! At some stage you should calibrate
the length of your delay line.