Oct

WARSAW, MO The Twin Lakes ARC will sponsor the Warsaw MO Hamfest Saturday. October 5th from 9 a.m. to 4 p.m., at the Warsaw Community Bldg., one block west of the square. Talk-in on 147.300 on the Warsaw rptr Setup is at 5:30 a.m. Admission S2 at the gate. 8 ft. tables S10 each (hurry, only 30 availableBreakfast and lunch will be sen/ed on site. For more info call Gene at 660-4388650. or E mail to [[email protected]].

SPECIAL EVENTS, ETC.

AUG 10, 11

MARYLAND-DC QSO PARTY On the air

1600-0400 UTC August 10th to 11th, and 1600-2359 August 11th. Suggested frequencies: 3.643. 3.92, 7.07, 7.23, 14.055. 14.268, 21.115, 21.37. 28.055, 28.38, 50.15. 52.525. 146.55, 146.58 and 446.00 MHz. Try CW on the odd half hours. Scoring: Add up your QSO points and multiply by the sum of the multipliers. Multipliers may be claimed once each and they do not repeat from band to band. QSO Points: 10 points per club station. 5 points per mobile station. 4 points per QRP station, 4 points per Technician

Continued on page 59 73 Amateur Radio Today - August 2002 43

Hboue & BEvONO

VHF and Above Operation

C.L Houghton W861GP San Diego Microwave Group 6345 Badger Lake Ave San Diego CA 92119 [[email protected] com [[email protected]

Converting Surplus: A1296 MHz 5 Watt Amplifier — Part 2

This month is a continuation of last month s column that concerned a 1 watt power ¿iniplitier PC board that we obtained in surplus for the 1296 MHz amateur band operation.

This time, the focus is on converting a higher power module that is capable of a minimum of 5 watts output andean be puslied to higher output power lev els. Then? is *xne similarity between the surplus nxxluk^ andcommercial modules that available for this same frequency band that do not require mtxlilicatiott. Existing modules are the older Mitsubishi M57762, see Photo Cand the newer Mitsubishi M67715 12% MH/ power amplifier 5 watt class niodules.TheMiteubisliinxxiilesaicaxtstmcted in black epox) aixl cannot be modified as they arc oHiipletelj sealed unlikethe Fujitsu surplu> module. fliey run from 12 volts dSrccth. and do not require minus bias supplies.

Photo A+ A picture of the internal workings of a Fujitsu FMC16I6LI0I5 power amplifier for die ¡600 MHz satellite telephone sen ice. Like most pow er modules that are sealed* this device has a cover that can hi pried open and modified. Please note that ¡here are four chip capacitors. This is w here additional 0.05-itich chip capacitors will be mounted piggyback on top oj the existing chip capacitor on the PC board amplifier to lower frequency of operation*

Photo A+ A picture of the internal workings of a Fujitsu FMC16I6LI0I5 power amplifier for die ¡600 MHz satellite telephone sen ice. Like most pow er modules that are sealed* this device has a cover that can hi pried open and modified. Please note that ¡here are four chip capacitors. This is w here additional 0.05-itich chip capacitors will be mounted piggyback on top oj the existing chip capacitor on the PC board amplifier to lower frequency of operation*

Comparing the Mitsubishi modules and the i :ujitsu module, they arc quite similar except thai the Fujitsu module Jili^ a remm metal cover It can be gently lifted off lo expose the circuitry of the amplifier PC board, allowing modification to the internal circuitry to make it useful at 1296 MH/. Modification details aiv* shown in Photo A. The Mitsubishi modules; are sealed in a black plastic epoxy case with two heat sink tins on either side and five connection leads protruding from the module case. No hint of circuitry is apparcm in the black modules. The cost of the Mitsubishi modules is a little e\pensi\ e, slightly over S60 last time I checked. A line module but costly.

When the Fujitsu modules were located in surplus and the details on their performance capabilities uere realized. we knew a com ersion Lo 1296 MHz was going to he attempted. Looking at the Fujitsu FMC 1616L1015 specification will show you the interest we had when its ratings were obtained. Its main frequency of operation is centered on about 1616 MHz and was intended for use in the Globalstur fixed telephone system. The PA requires +9 volts @ 2.5 amps, +7 volts I amp and -4 volts bias.

Power output is rated for +39 dBm using both the +7 and +9 vol I power supplies. Thai's I dB under 10 watts power ouLput when the final de\ice is run from a +9 volt power supply.

The circuit board is obtained from cutting the power amp module and its bypass capacitors out of the larger main circuit board. Originally, the amp is set up to run from a single +7 volts power supply .This produces originally about +36 to +37 JBm power output (5 watts is+37 dBm) at 1616 MHz. Power falls oft quite rapidly as frequency is lowered out of its normal frequency range of operation. That's w here changing circuit elements comes into place to increase performance ui 1296 MH/. Fortunately the module is not seated and the cover can be pried open and the required simple changes made to allow operation at 1296 MHz.

The plan was to see what could be done 10 modify the Fujitsu modules to 1296 MHz operation. My partner Kerry N6IZW figured out die values needed to convert the Fujitsu 1616 power module. The changes are easy. What is required is to increase four chip capacitor \ ¿dues to increase performance in the 1296 Mi • / band. The \alues selected are nearly correct (not optimized) and were selected because they were obtainable from our junk ho\. Other values varying 10 percent or so should work just as well as the values we selected. One 1.5 pF chip cap and two each 3 pF chips caps and a single 6.K pF chip cap did ihe trick. Fig. 1 shows the location where to place the additional chip caps on top of the existing chip on the power amplifier board.

As shown In die drawing, there are three amplifier devices surrounded with a couple of chip caps marked "C\ The four capacitors to be increased in value are shown with

Photo It, Test bench devices used for testing the amplifier include KF sweeper (nor shown) for RF drive. iw measurements I use both a Bird 43 power meter for coarse work and a HP432 power meter for nunc exact results, f like to use the Bird 43 RF power measurements and the HP432 and suitable attenuators to do the final exacting measurements*

Photo It, Test bench devices used for testing the amplifier include KF sweeper (nor shown) for RF drive. iw measurements I use both a Bird 43 power meter for coarse work and a HP432 power meter for nunc exact results, f like to use the Bird 43 RF power measurements and the HP432 and suitable attenuators to do the final exacting measurements*

a circle drawn around them individua])v. Other nearby chip caps are shown to pro-vidc a layout perspective oí the board's component pans. Resistors and other circuito' were nt>1 shown jus* Uie major chip capacitors to reduce confusion and give a perspective of die board layout as to which chip capacitors to increase in value. We used a small, miniature, 0.05-inch chip cap to modify the amplifier. [1'larger capacitors are used, the nece>sur\ amplifier cover might short them out to the coven w hich is ground when cover is reattached. We will supply the necessary chip caps with the amplifier PC board obtainable from the author

Instructions

Installing ilie chip caps can be dangerous*

Photo C Mitsubishi M57762 5-wan commercial 1296 MHz amateur band amplifier Note the large-style components used in this older amplifier This unit is sealed in black epoxy unlike the Fujitsu Module, A rebuild using chip electrolytic and bypass capacitors is in order After some S rears, this workhorse module still functions.

Photo C Mitsubishi M57762 5-wan commercial 1296 MHz amateur band amplifier Note the large-style components used in this older amplifier This unit is sealed in black epoxy unlike the Fujitsu Module, A rebuild using chip electrolytic and bypass capacitors is in order After some S rears, this workhorse module still functions.

especially it sou drop the chip caps on the floor or in a rug. A familiar problem comes when you grab them with a pair of tweezers: if you pinch them too greatly, twang, the chip cap fties off to never-never land. Best to work with good lighting on a sheet of paper oj something to give you contrast to the while chip cap. and work with only one at a time. Locate the first capacitor lo receive a piggyback chip cap. Add a small clot of solder to one end of this ciiip cap on the PC board. This is to facilitate receiving the nevs capacitor on top of the target chip cap, The solder dot. added to the cap w ill be enough to lack solder in plaec one end of the modification capacitor.

I use a small surgical tweezers to hold and position the chip cap in proper place and then just touch solder the chip cap's one end to the bottom chip cap. Examine position, and it all is OK, solder the other end of the chip caps together Resolder the first end over again to make it a got id connection and do not leave any solder spikes to short oui u hen the cover is placed back on. Additionally, the new chip cap should lie as Hat on top of the existing chip cap as is possible for cover clearance. Repeat the procedure for the remaining three chip capacitors to he so modi l ied.

DC power leads need be nothing more than standard stranded hookup \\ ire. 1 found a short section of stranded 20-gauge w ire that must have had 50 different color conductors- Striping the insulation cover produced several different colored wires: black, red. green, blue, yellow, to mention a few, I purchased a > to 10-toot section of the eahie and cui it up into 1- and 2-foot sections for a wire junk box. Ifs proven to be quite handy. When I need bias I pull yellow, ground black and +DC red, or whatever color needed lo run simple wiring needs. It's worked out well over the years. I 'm süll working on the 5- or 10-foot section I stripped down to the wire box.

For coax connections, look for small diameter microwave-rated shielded coax with a connector you normally use, like an SMA male or female connector, attached to one end. It's good material to add to your junk w ire box, be it hard coax line like. 141 solid copper jacket or iis smaller brothers the ,085 and .04! hard line. It all has its uses and will be used on a projcct sooner or later. The .141 solid jacket coax is a little hard to form to mv needs but the smaller variety (.085 and especial J > Lhe .041 \ bend and form to fit tjuite well tor circuit modifications, especially in light soldering spois,

Don't use RG-174 miniature coax, as it tends to be too lossy and the soft insulation

©

Was this article helpful?

0 0

Post a comment