Receivers for Jupiter
What is needed?
Jupiter's radio emissions may be heard from Earth on frequencies ranging
from about 14 to 38 Mhz. I suggest you pick a frequency between 18 and
28 Mhz for the greatest likelihood of success. Below this range atmospheric
refraction will usually hinder your ability to hear Jupiter. At the upper
end of the Jovian decametric spectrum signals are likely to be weaker.
Most good short-wave receivers have an upper cut off 30 Mhz and so cover
this range. High frequency ham band equipment can also be found with coverage
of key portions of the suggested range. Ham bands are found at 18, 21,
24, and 28 Mhz.
AM or Product Detection
You can't hear Jupiter on an FM receiver. You need an AM or a product detector.
If you have a choice between AM and product (sometimes marked CW or SSB)
detector try them both. I like the product detector because it allows me
to hear when a carrier is encroaching of my frequency.
External Antenna Jack
Some cheap receivers do not have an external antenna jack. You will have
to add one yourself if you don't have one. You can't hear Jupiter on your
little whip antenna.
Jupiter's signals are quite broad banded. The L burst features typically
can be hundreds of kilohertz wide. Short term frequency stability is thus
of little consequence unless you are trying to stay within a narrow range
of frequencies to avoid terrestrial interference. A receiver which does
a poor job of staying tuned to a narrow band voice signal may be perfectly
adequate for Jupiter.
You do not need a receiver with expensive crystal IF filtering to hear
Jupiter. Actually, a broad IF selectivity position of 15 kilohertz
or more is quite desirable. Again, the exception here is when you are trying
to fight narrow band interference. In that case, good selectivity is needed.
Front end selectivity of most receivers is adequate, however, if you experience
interference from out of band signals, you may want to add an additional
stage of passive filtering ahead of the receiver. A single tune circuit
will usually suffice.
While some older tube type receivers were poor performers at the upper
end of the short-wave spectrum, most modern receivers have plenty of front
end gain and sensitivity. How can you tell if your receiver is sensitive
enough? A simple test can be done by switching between your antenna and
a 50 ohm resistive load. Tune away from any stations so that what you hear
is a unmodulated static hiss. Turn up your RF gain and adjust the volume
to a level where the hiss is annoying. Now switch to the dummy load. The
volume should drop dramatically to comfortable level. If it does this,
your receiver is probably sensitive enough. If the difference is minimal,
you are going to need some pre-amplification. If you use a preamplifier,
try to find one that falls into the category of a preselector. Those
broadband transistor preamps that can be purchased for less than $20 usually
add more problems than they solve. Broadbanded preamps introduce intermodulation
products and desensitization problems. Yes, they can actually reduce your
sensitivity to the cosmic signals by blocking in the presence of strong
local signals. You need a tuned circuit in front of the amplifier, that
is, you need a preselector.
Automatic Gain Control is a feature found in most every receiver to help
eliminate annoying changes in volume when listening to communications.
This AGC can mask the very signal we are trying to hear. Thus it is desirable
to have some way of turning this feature off. Look for an AGC switch. It
is a plus. Sometimes, a savvy technician can modify a receiver to disable
If you live in the city like me, you will find a noise blanker to be a
wonderous if not indespensible feature for Jupiter work. Noise blankers
remove strong short duration noise spikes before they reach the audio stages
of the receiver. Unfortunately, noise blankers are usually only found in
quite expensive receivers. Noise blankers vary in how well they perform,
so try to get a demonstration of the unit's abilities before you pay a
lot of extra money for this. If you live in a low interference environment,
you won't need one.
The Jove Receiver by Richard Flagg
I had not intended to suggest a receiver for Jupiter but this is a good
deal and I have seen it work! Richard Flagg developed a small receiver kit
primarily to be used in schools for a Jupiter class project, however, it
is also available to the general public for a very reasonable cost. It
comes with an antenna kit. Radio-SkyPipe software can then be used to record the envelope
of the Jupiter signal using a PC and sound card. The manual is for the
Radio Jove Receiver excellent. See http://radiojove.gsfc.nasa.gov/
There is a lot of room for experimentation using some of the small kits
now available. I don't know if any of the regenerative receiver kits would
work in this application. I would expect that they would be too unstable. Ten Tec has some interesting and inexpensive
direct conversion receivers which might work. I haven't got around to making
one but it would seem that a single NE602 chip would make a wonderful downconverter
for an AM car radio (car AM radios have an antenna jack). Don't forget
the used market, hamfests, and surplus outlets. This doesn't have to be
an expensive project. Don't forget! No matter how good your receiver is
you are going to need the right antenna to hear Jupiter!