Listening Post Accessories
|For the best in selectivity, intelligibility, and long-term listening enjoyment,
try adding some helpful accessories ahead and after your favorite receiver.
I guess it's undeniable, radio is in my blood. I have been SWLing since the early 1950's, had my first taste of Ham Radio in
1959. I have been a communications products designer for more that 45 years, and served as a communications intelligence
(COMINT/SIGINT) specialist with the US Army Air Defense Command and Signal Corps. More recently, I've owned and
operated a TSCM (Technical Surveillance and Countermeasures) accessory equipment business. I just can't leave it alone.
Some may call it an obsession, but I call it a passion ... a passion to communicate with all corners of the planet ... and beyond
As one's hobby, or profession, experiences advance over the years, it's only normal to desire, or require, better quality equipment. In concert with that maxim, I have been experimenting
with various "receiver helpers" over the years. The apparent logic is that a receiver is a radio that is only as good as it is applied, used, and operated. It's a tool that doesn't do anything
without external means; namely an antenna, and in the case of good commercial, professional receivers, a decent audio reproduction system. My decades-long experimentation with
various antennas, antenna feed systems, noise abatement and grounding, signal preselection and preconditioning, and recovered audio reproduction have led me to this particular
milestone. Below are two of the receiver accessories that I have boiled down from many years of design, research, and development. One unit, the RFP-1, deals with the incoming RF
signal. The second unit, the ACP-1, handles the chore of processing the receiver's audio.
It should be apparent that I am a huge fan of Watkins-Johnson equipment, so it was only natural that the two homebrewed devices match the cosmetics of the iconic "W-J look."
Beside my two units, the above photo shows the WJ 8718/MFP. WJ 8718A-9 receivers, and a DMS 105A-2 demodulator; it's a pretty respectable LP.
Not to be discriminatory, I should also direct you to some of the other manufacturers for whose products I hold great affection, here.
A couple of views of the RFP-1 (middle), the ACP-1 (top), and a W-J 8718/MFP.
The lower unit is the RFP-1, which is an RF signal parametric filter (preselector), a signal preconditioner, and receiver multicoupler (output splitter distribution amplifier). The unit also has
a calibrate function for 100KHz incremental marking, and an LF, VLF up-converter for 10MHz recovery. The system has been tested to below 20KHz.
The ACP-1 controls the received audio from four receivers (audio mixer), has various band-shaping audio filters, can select the IF signals of four receivers and redirect them to external
demodulators, and an audio power amplifier output to drive different speaker lines.
This ACP-1 is a basic audio mixer with a 5K ohm
mix bus, a preamp for line level output and +/-
about 12dB of tone compensation at a 1KHz
indicator LEDs, only because it makes the
operation of a device with so many controls
much easier -- red=off, green=on, and
The power amp in the second schematic is
about 7 watts with a separate drive for the
The system also provides aux. outputs for the
mix buc, pre-control, and post control, a la any
standard recording or broadcast console.
Meters are provided for "VU" for recording and
"line" gain control and for total power to the
The RFP-1, which is described elsewhere on
this site, contains a parametric filter that covers
from about 20 to 30 KHz well past 30 MHz and is
capable of functioning past the 6 meter band.
The filter is passive and functions at the 50-ohm
line. The absence of impedance transformers is
to not allow the time and phase distortions of
fast transient noise and lightning crash static,
and the subsequent inability of noise abatement
with various noise blankers and noise limiters.
Four receivers can be assigned signal from a
low-loss multicoupler. Likewise, four antennas
may be selected.
Input protection is employed as is a matching
transformer which may be switched out of
service. Broad impedance matching may be
used from about 36 ohms to about 1200 ohms.
Two companions to these units will be a
Dynamic Noise Blanker and Automatic
Noise Limiter (NAC-1) [Noise Abatement
Controller], plus an Antenna Diversity
Controller (ADC-1). I am currently working on
the design and beta testing for that device.
All units are built on 3U (3 rack units) chassis,
rack handles from W-J surplus, and front panel
decals made in Pagemaker (Adobe), vinyl
laminated, and glued in place.
I will report on the progress of that item after
some therapy - this past year has been very
intense in getting these two items finished,
tested and documented...so I think I need some
time under the pines in the hammock.
RW Betts, N1KPR
Rear view of the two units
at the bottom of the page
Top unit; ACP-1: (Audio Control Panel)
Starting at upper right is the input for audio from four receivers. Directly below that are the four BNC connectors for input of the same receivers' IF signals. There's a Line
Loop for adding a graphic equalizer, DSP noise reducer, etc. Then the audio from either of the two demodulators and below that the BNC's to feed those demods. You
can use any or all of 3 speaker systems or feeds and there's taps for Pre, Post and Line outputs for recording Air Checks or as a Signal Monitor for remote monitoring
Note that the two Demod loops are front panel selectable, and the Demod audio is fed to the audio mix bus with individual input level controls. So it is possible to listen to
the receiver's recovered audio, and at the same time compare it to the same receiver's IF feed audio from the Demodulator. This allows the operator to select the best
recovered audio and aid in making appropriate filter selections on the receiver and/or demodulator.
If the IF Demod inputs and outputs are not used, the ACP-1 can be considered nothing more than an integrated 4-Input audio mixer (with power amplifier), and various,
flexible tone control.
Bottom unit, RFP-1: (RF Panel)
Four antenna inputs and four antenna feeds for the four receivers associated with the ACP-1. Between the inputs and outputs are all the preselector, 100KHz marker,
LF/VLF 10MHz up-converter, preamplifier, antenna selection, output feed multicoupler control, and impedance matching circuits.
|But wait ... there's more ...
The mantra I've been reciting forever, or so it seems, is a simple law of physics, engineering, and common sense. It's undeniable, irrefutable, and impossible to ignore. This axiomatic,
self-evident truth is the first rule of all communications systems designers: "The receiver is only as good as its diet."
So, above you can see how I addressed two of the more apparent areas of the received signal stream; the input is fed from a preconditioned RF signal, and the output is tailored with
recovered audio management. That should cover everything pretty well -- the input and the output. Right? ... Wrong!
All this equipment runs on electricity. We assume, or presume, or have faith, or (at least) hope, that the power fed to our equipment is just plain old sinusoidal-wave current flow from a
constant voltage source. Okay, generally it is. But more often than you may like there is some free electricity that comes along with the deal. Sometimes free stuff might be an
undesirable gift. This extra electricity comes to us as transient spikes, high-current surges, triangular, square and saw tooth-shaped buzzes, hums, whines, burps, and whistles. In
terms of overall power, there ain't much of that bad stuff. Actually, it's usually just a very tiny, small percentage of the overall power consumption. But guess where it resides. Yup, right
on top of the power company's sine wave ... just like a good old AM signal. Nice, huh? Radios vary greatly in power supply design, but even some of the best kilobuck radios can fall
victim to power line noise intrusion.
Enter the PCU-1 and PLC-1. These are the "Power Control Unit" and "Power Line Conditioner" respectively. Below is a sneak preview of the nine-device switched controller. The actual
"conditioner" (blue meters) incorporates several types of transient, pulse, and impulse clamps, along with noise or "hash" filters, and a magnetic/induction sine wave smoother. Also
incorporated is a 12 Volt DC to 120 Volt AC inverter with all the attendant filters and clamps required for that RFI-frightful mode of conversion. But it's all worth it. The result is nice,
steady, clean, pure sine wave AC power. And it tastes so delicious ... to the receivers, that is.
The AC power conditioning and 12 Volt inverter unit will supply about 1,800 Watts of continuous line power, with peak-demands of 2,400 Watts. That should more-than suffice for a
So if you are interested in this triad of receiver aids, stay tuned. And yes, I will be happy to present the schematics and assembly details for your homebrewing pleasure.
Once again, I apologize for the
poor pics, but photographing
something that is a light source,
is something I have not mastered
At left is the PCU-1 Switched
Controller. It's nothing more than
a 15 Amp circuit breaker, a
Master switch and 9 lighted
output circuit switches.
Below that sits the PLC-1, Power
Line Conditioner. It features line
Voltage and Current draw meters.
To the right are the switchable
RFI, EMI, and EMP filter
switches. The only reason they
are switched is in case of a
failure due to some very large
surge, a nearby lightning strike,
or other catastrophic event. The
green LEDs indicate that all is
well with each filter.
The current, but temporary, Watkins-Johnson
The PCU-1 Switched Power Controller
PLC-1 Power Line Conditioner and Filter
SDM-1 Demodulator; 5-way detector.
ACP-1 Audio Control and Shaping Panel with Demodulator Audio.
RFP-1 Preconditioner and Preselector with output Multicoupler.
W-J 8718A Receiver - Same as above, but manual control.
W-J 105A-2 Demodulator
W-J 8718A/MFP Receiver (5KHz to 30 MHz.)
Please scroll to the bottom to see the final, completed LP.