Kerv

Cutting Holes in

When you bring a transmission line into the shack, many times the most obvious route goes right through a window screen. Much to the consternation of the XYL, many hams are apt to stick a screw driver into the screen and spread the strands a little bit, A neater method Is to use a conventional chassis punch about a half inch in diameter. To prevent the strands from unraveling, several techniques may be used.

Window Screens

If the screen is brass or copper, the strands around the opening may be soldered together, For aluminum or plastic screens, a little bathtub caullc does a marvelous job. If care is taken in choosing the size of the chassis punch, the cable will fit snugly in the opening and no insects will get in. Furthermore, if the iole is placed near one of the corners, it may be patched up later with little notice Jim Fisk W1DTY

Jim Fîsfc WlDTY RFD I. Box 138 Rindge, N. H. 03461

International Crystal

SBX-9 Sideband Exciter

If you're one of those fellows who has been procrastinating about getting on YHF sideband, the new International Crystal 9 MHz sideband exciter is just what you're looking for. The high frequency addicts can read on too, because the SBX-9 is equally suitable for any of the ham bands below 30 MHz. Basically, this new exciter from International Crystal is a crystal controlled 9 MHz single sideband generator with selectable upper or lower sideband. It uses a very steep sided four crystal half lattice filter in conjunction with a 7360 balanced mixer to obtain a minimum of 45 dB carrer suppression with at least 40 dB suppression of the im wan ted sideband.

In all, the SBX-9 uses four tubes to generate 0.5 volts of 9 MHz sideband energy across the 50 ohm load. In the input a high impedance dynamic or ceramic microphone is used to drive a 12A XT audio amplifier; this audio signal is fed into one side of a 7360 balanced modulator* The control grid of the balanced modulator tube is fed by

SBX-9 Specification»

Frequency: 9 MHz crystal controlled.

Operating mode:

RP output:

Sideband generation:

Selectable upper or lower single sideband.

0.5 volts across 50 ohms.

Four crystal half lattice filter. Carrier suppression 45 dB minimum. Unwanted sideband suppression 40 dB minimum.

Audio input: Hig-h Impedance dynamic or ceramic microphone.

Tube lineup:

Features:

Size and weight: Power re-

UBH6 oscillator, 12AX7 audio amplifier, 7360 balanced modulator, 6BAG rf amplifier.

Push to talk relay; front panel control of balanced modulator; full metering- of rf output for balance adjustments*

12 pounds. 115 volts ac, 50/60 Hz, 36

quirements : watts.

Price:

$125.00

the 9 MHz rl carrier which is generated by a 6BH6 crystal oscillator stage. The carrier is balanced out in the 7360 by the balance control which is connected to the tube s beam deflection plates. When the audio signal reaches the 7360, the balanced modulator becomes unbalanced at an audio rate and produces a dou )Ie sideband suppressed carrier signal. This signal is fed into a crystal filter where the undesired sideband is suppressed and the desired sideband passes through to the grid of the 6BA6 rf amplifier. The desired sideband is selected by choosing the exact frequency of the 6BH6 crystal oscillator. Since the 2 kHz crystal filter is centered on 9000,00 kHz (9 MHz), the upper sideband will pass through the filter when a 8998,5 kHz crystal in used in the oscillator; conversely, the lower sideband will gel through if a 9001,5 crystal is usedL Because of the steep sides and narrow passband of the crystal I attic filter, the audio sideband outside the filter passband is suppressed some 50 dB. The 6BA6 rf amplifier is tuned to MHz and feeds the 50 ohm output through a link coupled to the plate tank.

There is a test switch provided on the trout panel of the exciter which unbalances the balanced modulator and keys the push to talk relay. This is used where a carrier is necessary for adjustment of an external power amplifier or mixer. The internal push to talk relay has a number of contacts which are brought out to the accessory socket These auxiliary contacts may be used for turning on external power amplifiers, switching antenna changeover relays and mnting receivers and converters.

Since the SBX-9 has a fixed 9 MHz output, the front panel has a minimum number of controls. In fact, to put it on the air all you have to adjust are the carrier balance and audio gain controls, And, once the carrier balance is set, it requires very little further attention, A 100 microampere meter is connected across the plate circuit of the 6BA6 rf amplifier to measure the amount of carrier. All the operator has to do is

International Crystal SB A-50 50 MHz SSB Mixer-Linear Amplifier turn the SBX-9 ons key the push to talk relay and adjust the balance control lor minimum indication on the meter; then talk into the mike and adjust for proper audio gain as indicated on the meter. The complete adjustment takes only a couple oi seconds and results in a minimum of 45 dB carrier suppression.

The SBX-9 is designed primarily as an exciter for the SHX-50 50 MHz mixer-amplifier, but it may be used with homebrew mixers on other amateur bands by the proper selection of frequencies. The use of a 5 MHz VFO and suitable mixer-amplifier circuits for instance would provide single sideband on either 75 or 20 meter phone. Other frequencies may be added by the addition of appropriate crystal controlled mixer stages.

The sideband signal from the SBX-9 is very clean on the scope and sounds very crisp and sharp. The high quality crystal filter and use of double tuned circuits rest] Its in high efficiency with maximum suppression of undesired signals. For the amateur who is interested in getting on sideband without going to a transceiver, particularly on the VHF bands, the International Crvstal SBX-9 is an ideal choice.

The new international Crystal SBA-50 50 MHz single sideband mixer-linear amplifier was designed as a companion unit for the SBX-9 sideband exciter for operation on six meters. This dandy little transmitter takes the 9 MHz sideband output of the SBX-9, mixes it with a crystal controlled signal in the 41-45 MHz range and puts out

10 watts of single sideband single tone on six meters.

The circuitry of the SBA-50 is quite straightforw ard, starting out with the I node half of a fit78 in a simple third overtone crystal oscillator circuit to provide the necessary output on 41 to 45 MHz, If VFO operation is designed, it may he connec to the SBA-50 through the accessory socket on the rear deck oi the unit However, one of the three crystal positions must be va cated and that switch position used when (he transmitter is VFO controlled. The tetrode half of the fit'8 is operated as a VHF mixer. In this section of the 6U8 the 41 to 45 MHz signals from the crystal oscillator are heterodyned with the 9 MHz signal ironi the single sideband exciter. The resultant sum frequency at 50 to 54 MHz is selected by the tuned mixer plate circuit and inductively coupled to the grid circuit of the 12BY i linear buffer amplifier. This six meter signal is further amplified by the 6360 linear powei amplifier and link coupled from the power amplifier tank circuit to the 50 ohm coaxial output. This signal may he used for communications within the six meter band or used to drive a larger linear power amplifier.

SBA-50 Specification»

Frequency coverage:

50-54 MHz, Three crystal conro31ed channels select^ a f>le from ihe front, panel or external 41-45 MHz VFO may be used.

RF output;

10 watts single sideband single tone.

P^F drive required:

D MHz single sideband, 0.5 volts across 50 ohms.

Output i rnperiance:

50 ohms nominal.

Tube lineup:

6U8 crystal oscillator;VHF mixer, 12BY7 linear buffer amplifier, 6360 linear power amplifier plus two o i voit-

aixe regulators.

Crystals required:

3rd overtone type in the Ml-lz range; three crystals furnished with unit.

Features;

Crystal or YFG control; provision for external push to talk control; complete metering oi' 0 MH* drive,

oscillator grid* buffer grid, power amplifier grid and rf output.

Power requirements

115 vults ae, 50/60 Hz, 37 watts.

Sizr- ■ i ti11 weight:

x x 9-9/16", 13 pounds.

Price;

$145.00

>

iOI

You won't be able to put it down!

We should give fair warning to those who order this new book from the Radio Society of Great Britain. Once you pick it up, you won't be able to eat, sleep, talk or watch TV until you've read it alL It's a fascinating, densely-packed, IQO* page book full of every imaginable practical circuit for ham radio. Hundreds of circuits and ideas are discussed, and each one is useful to hams. Here are the chapters: semiconductors, components and construction, receiver topics, oscillators, transmitter topics, audio and modulation, power supplies, aerials and electrical interference, troubleshooting and test equipment. Once you've digested this book thoroughly, you won t be able to build or modify any gear without consulting it.

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