Receivers for Jupiter

What is needed?

Frequency Coverage...

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 shortwave 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.

Frequency Stability

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.

Selectivity

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.

Sensitivity

While some older tube type receivers were poor performers at the upper end of the shortwave 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 preamplification. 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.

AGC Switch

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 the AGC.

Noise Blanker

If you live in the city like me, you will find a noise blanker to be a wondrous if not indispensable 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 Dick Flagg

I had not intended to suggest a receiver for Jupiter but this is a good deal and I have seen it work! Dick 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 and even software to let you record the envelope of the Jupiter signal using a PC and sound card. The manual is excellent.

Click here to find out about this NASA sponsored project.

Last Thoughts...

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!