Preselectors can add life to your receiver with even a small antenna. The added advantage to having an preselector is that it can attenuate other signals from overloading the front end of your receiver. However if not properly tuned, a preselector will permit adjacent signals to overwhelm your receiver. This is even more evident in less expensive receivers.
I picked up the Palomar P-508 on the recommendation of another SWL and boy I am glad I did. The Palomar P-508 covers from 200 kHz to 30 MHz with-in five band switches. (200 kHz - 550 kHz, 550 kHz - 1600 kHz, 1600 kHz - 5000 kHz, 5000 kHz - 14 MHz, 14 MHz - 30 MHz). The other two knobs are the AT-GAIN (the preamplifier gain control and attenuator) and TUNE (for fine tuning the preslector). The rear antenna jacks are standard SO239 connectors. The P-508 is powered by 12-volt wall wart.
Operation is fairly simple. After turning the unit ON, put the AT-GAIN and TUNE knobs at 12 o'clock, set the band switch to correspond with the frequency you are listening to and rotate the TUNE knob for strongest signal. If the signal is fairly weak, tune the AT-GAIN just enough to make the signal audible and enjoyable. Remember, by increasing the AT-GAIN, you are also increasing the noise level.
I have used this unit on 3 different radios with varying results. The P-508 really shines with an old Kenwood R1000. This Active Preselector greatly improved reception on MW while improving reception on SW somewhat. Front-end overload has never been a problem with the R1000 but it is with my Sangean ATS 909. Living near a metropolitan area and also have a 1kW MW station less than a mile from you house can create some interesting situations. The P-508 does a great job with the Sangean in attenuating unwanted signals through out the MW and SW bands. The P508 is of little or no use at all with the Drake R8B. When the P508 is turned OFF, it is passive and still permits reception from your external antenna.
The only thing I dislike about the P-508 is the 1/8" plug for the power supply. I think it would have been better to have utilized a DC power plug instead.
Unfortunately Palomar Engineers has discontinued production of their preselectors however other preselectors are available from other manufactures. MFJ manufactures various models and AMECO has the TPA with a built in telescopic antenna and connectors for an external antenna. If you are able to find a used Palomar P-508, don't worry that it can not be repaired. Recently, after a thunder storm, my Palomar P-508 stopped working. I dashed off an email to Palomar Engineers hoping that they would repair the unit but honestly expected them to say no. To my infinite surprise they told me to send it to them with a check for $35. They flipped the P-508 back to me in less than two weeks and it worked as good as new. Hopefully they will reconsider manufacturing these great preselectors again.
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