New Concept

in 2 METER FM OMNI

Again. Out of research comes increased performance. Avanti's unique ARli-257 2-meter FM orani is engineered to give you more gain and all around higher performance than any other antenna of its type or price. The patented tapered skirt configuration produces 4.17 db gain (measured over Vi wave ground plane! plus a low angle of radiation that has proved effective in Eliminating dead spots. No coils or transformers to detune or burn out . . . unaffected by temperature and humidity. The small projected area and light weight provides easy mounting and gives wind survival to 120 MPH.

Construction is all aircraft quality aluminum and fiberglass. Antenna comes complete with coax lead, mounting hardware and liberglass mast current eliminator.

Other frequencies from 140-175 MHz are available upon specification.

SPECIFICATIONS:

Bandwidth—¡»0.5 MHz Polarization—Vertical

Impedance—50-52 ohms Connector—PL-259

$4495

33-35 WEST FULLERTON AVENUE, ADDISON, ILLINOIS 60101

AMATftX

AVANTI RESEARCH & DEVELOPMENT, INC. We also have a complete line of high performance mobile antennas.

The 3.0 kHz crystal or mechanical filters now in general use for SSB reception generally have excellent skirt selectivity, but the nose bandwidth is too broad for satisfactory CW work under crowded band conditions. Undoubtedly the best solution is a commercial narrowband filter, but these are expensive, often hard to obtain, and may be difficult to fit into an existing unit. A parallel i-f strip or "Q-5-er" is a relatively clumsy and complicated method and the use of another mixer stage to get down to an i-f of 50 kHz or so adds to overload and cross-modulation problems. Filters at audio frequency are of limited help, as strong adjacent signals are still amplified before detection and by overloading punch holes in the desired signal.

A relatively cheap and simple solution is to follow the 3.0 kHz filter with a single crystal gate. This provides sharp nose selectivity while the 3.0 kHz filter helps with the skirt selectivity. The circuit shown uses no tuned normal conditions, is a few kHz higher in frequency than the series resonance. Overtone crystals will work in this circuit at overtone frequency.

Start by testing the circuit with the crystal switched out and the trimmer disconnected. Check that the electrode voltages are correct and that the stage is providing normal gain. Now switch in the crystal and slowly tube across the pass band, monitoring the i-f output with the existing S-meter or a VTVM. A rather poorly defined peak should be found at crystal series resonance. Tune to one side of this peak and connect up the neutralizing trimmer and adjust it for minimum output. Now sweep slowly across the passband once more. A very sharp peak should now be apparent. Continue adjusting the trimmer and ■sweeping the passband until you get a symmetrica] peak. My crystal required 4 pF, but this value will vary for other crystals. Finally, tune to the crystal peak, switch the crystal

Electronic Overload Relay Avanti

ADDISON, ILLINOIS 60101

AVANTI RESEARCH & DEVELOPMENT, INC. We also have a complete Eine of high performance mobile antennas.

BASE LOADED 2-METER FM 5/8 WAVE GROUND PLANE

Another Avanti 1st. The ARD-250 is a high performance easy to install ground plane that will give years of reliable service. Our loading coil is hermetically sealed in Cycolac to prevent detuning in corrosive or high humidity atmospheres. The rest of the antenna is all aircraft quality aluminum. The radiator and radials are 5/i6" solid aluminum and thread securely into the coil. Direct ground construction allows static dissipation for low noise ratios.

The ARD-250 is factory tuned but may be field trimmed by simply using a hacksaw. Other frequencies from 140-175 MHz are available upon specification.

SPECIFICATIONS:

V.S.W.R. 1 .5:1 or less Bandwidth-±3.5 MHz Impedance—50-52 ohms

Power Handling — 250 watts intermittent 1 50 watts continuous Pol a rlzation —Vertical Connector— PL-259

circuits and may simply replace an existing first i-f amplifier tube without any material loss of gain. In my case, a combination of a small Japanese HC 6/U filter crystal at 455 kHz following a 2.1 kHz bandwidth Kokusai crystal-mechanical filter gave a bandwidth of about 220 Hz at-6 dB, 600 Hz at -20 dB, and 3 kHz at -60 dB. Where the unit is incorporated into existing equipment the crystal can be switched out by a small relay or a low capacity diode switch. In a transceiver, where the first i-f stage is common to both transmit and receive modes, this relay or diode could be coupled with the normal transmit receive switching so that the crystal is never operating on transmit.

The triode stage acts as a cathode follower giving a little less than unity gain. Signals, at the series resonance of the crystal, pass through it and are amplified by the second stage, which is a conventional pentode amplifier, The small capacity from the triode anode neutralizes the parallel capacitance of the crystal and its holder, which would otherwise couple unwanted signals through to the second stage. Setting up the unit is simple, once you have obtained a crystal with its series resonance falling within the SSB filter pass band, Remember that most crystals aie specified for parallel resonance, which, under

Simple Amplifier
Fig. 1. A sharp i-f amplifier circuit for CW selectivity.

out and observe any change in gain. If the gain is lower in the 3.0 kHz position, decrease the value of the grid resistor of the pentode stage, or vice versa, until you have equal gain at both selectivity positions.

The degree of selectivity possible with the circuit described demands high stability at both receiving and transmitter ends.

If the other chap comes back with drift and chirp at fifty words per tninute, you will just have to switch to 3.0 kHz selectivity to copy him!

to switch to 3.0 kHz selectivity to copy him!

j H ELECTRONICS j A Subsidiary of Cubic Corporation EASTERN OFFICE SWAN FACTORY P.O. Box 2286 /I 305 Airport Rnad Ocean, New Jersey 07712 Oceanside, Ca. 92054 Phone: (201) 431-0707- Phone: (714) 757-7525

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