Sw-7800 Schematic

I've been a ham now for almost 25 years There's a let of enjoyment goiten from Talking to new and old fnends on the ham Dands However as with any other hobby, a person craves to branch out and expand his or her horizons In my case, J thought It was Lime to Iry shortwave listening again as I had when I first started out. Since all my old shortwave gear Is long gone, I needed something new to gel back into generai-coverage receiving while at the same lime noi spending a smaif fortune. Heath's great new SYV-7&00 general coverage receiver kit seemed ihe way to go. l will ailempi to explain my trials and uiumphs in building this little gem.

Since all my gear Is Hcathklt I naturally considered rhem first In purchasing a new rig. They nad jusi introduced their SW 7600 general-coverage recclw and! believe it or not at a 10** discount Since the kit prtce o! SM9 95 was fairly reasonable to begin with, an extra S35 discount was the clincher.

1 realize That more money will buy more sophistication, but my criteria were rather simple; digital readout and digitally*syn-Ihesfred, I-kHz resolution or bettef ai a reasonable price wiih a self-contained power supply, Broadband tuning, aryf 0NI AMfSSS capability. FM was desirable but not necessary.

I sent for me instruction manual first to oe able lo check out consirucilon and schematics. Within 10 days the manual was on my doorstep and £ days later the order was in the mail,

I deducted ihe price oi me manual when I sent in my order as Is customary with Heathkit, but wnen the tar arrived I found another manual inside the box* However, Ihe enclosed manual had a 12-page cor recllon booklet wllh it. The changes range from text errors on the circuit boards to ru placing whole pages in Ihe Instruction manual, A small envelope of parts is pack aged loose to be used for replacing incorrect or modified parts, i would imagine that in the fulute these changes will be i¡v corporated into any revisions

The first thing that you notice when opening the carton is the careful packag ing of the components. There's a sheel of paper just inside the carton that explains now the box is packed and divided into dlf terent sections. You are instructed to unpack only the section thai is called for in the manual Each group includes a circuit board, parts, and hardware to complete tha- section of the manua1

Construction

As Is usual with Healhklth construction Is very detailed. Just make sure that you take care of the errata sheets before you begin construction! In addition to the Dags of loose parts there are taped com ponents." These are trie resistors, capaci tors, and inductors that are fastened to a tape strip lo simplify construction. The component are on the lape iirip in ihe order in which they are used, and Heathkil

1985 Ham Radios

tfeatt's SW T9QQ receiver f tfeatt's SW T9QQ receiver

1985 Ham Radios

Specifications

Frequency Cover* fle: Frequency Readout: Readout Accuracy: Frequency Control Modes; Sensitivity:

Setecirvtty-

Shape Factor Imago Rejection Dimensions: Muting: Recording:

Antenna Connexions:

Power

Wteight:

150 KHI to 30 MHz In 30 i-MHz ranges Digital, 5 LED digits Nearest 1 kHz

Synihesirad, PLL and IX vfo

CVWUSB, LSBh AM iwide and narrow!

SSB/CW—less than 0.35 microvolts for 10 dB (S NVN

SSB/CW and AM narrow— 2-5 kHz minimum at 6 dB

55 dB minimum

External jack foi transmitter

Miniature phone Jack dr fronl panel

About pounds assures you thai when taking parti, inventory before construct ionH it is noi necessary to check the laped components because they've teen checked at the factory.

Chassis assembly la straight forward. Take your lime with tht vernier drive mech anism —mare sure that the drai cord is Aound on the assembly just right. Don't hesitate to wind it ovor and over aftjln un-ill it's perfect. After all. that tuning knob is going lo Iravei many miles over the life of the receiver and you don't want to cuss at it every revolution along ihe way1

When assembling the readout circuit board, make sure lhat the LEO digits are in enact alignment. Even though there isn't much error oossibie when the numerals ate inserted inio the circuit board there is enough to make the digits fehghily crookeci and the job look sloppy You'll certainly notice It the frrst time you lurn on the rig.

When assembling the controller circuit board, the only precaution to take is the soldering of the *<co'v form verier power-supply sh-eids. After the shields are soldered to ihe board to lorm a ^o* around the circuits, you are directed to solder the corners of the shields to prevent rf Jeak-age. Since the shields form three sections. Ihe two Inner partitions are a Utile tough lo solder. Make sure you have a 35-40-Watt tip on your soldering iron Eo do the job. The metal shields act as a good heat sink and quickly carr, away the heat before a good solder bead has a chance lo form,,

The receiver circuit board is the largest board in lhe unll and therefore takes the most time, The components on ihe tape strip really save time here. Even so, allow 8-10 hours to do Ihe |0b.

The Synthesizer circuit board has the components mounted close together, so be careful ol solder bridges A solder sucker will clear any solder bridges, but l prefer solder wick (which Is simply wire braid) to do the job,

I said earlier that the components on the I ape strip were already checked and need not b^ inventoried agar. However out of habit it s a good ¡dea to check the pari against the manual as It Is installed This worked lo my advantage on this circuit board because a 0.01-^F glass-ceram lc cupacltor was substituted ror a Q.T-jiF unit. A quick check of Ihe pans nsi, taped component chart, and schematic confirmed that tl should be 0.1 ^R i can honestly say this is the first trine in my many years of Heaihkit building thai I've encountered thu, A quick chetk of my parts box produced a suitable 0.1 >F capacitor and I was off and running again, in the meantime. I firno olf a warranty claim and 2 weeks later I received the correct value capacitor in the mall.

The matching transforms* on the receiver board has to be wound by hand us-ng fine^gauge solid enameled and a femte co:e ail supplied, oi course Keep pressrng the wires against the core as you wind Ihe turns and you'll have no problem Be sure to use an object tnat won I scratch the eftemel off of the wires when pressing the wires against the cord.

installing the receiver board Is a little tncky The onty real interference as from tne ac-irtpuL terminal bloc^ near the front of the receiver Keep the line cord. 13-V-dt Inpui cable, ime capacitors, and resistors tight agamst Ihe terminal block and close to the chassis. That way the iarge receiver board will slip easily into place

Alignment and Testing

The test and alignment procedure for

Heathkit 7800

fn&tdû the SW T8Û0 The recw/ver PC board is mounted Oetow the ft/bcftess'S.

70 73 for Radio Amateurs * August, 1985

The S W 7800 receiver boars Af top rtght >s the dc power supply the fermer drive can Oe seen fust below FL4Q2

each boa ret is only a few paragraphs "ong and consists mainly of adjusting coils and checking voyages- i recommend a digital voltmeter tor checking the voltages since Ifi easy to measure to the nearest one-tenth voJt,

As soon as you turn on the receiver for that first alignment check, you should hear background hiss from ihe speaker. From then on you're home free. After zero-beating against wwv at 10 MHj and adjusting the SSB section of the receiver board, it s just a manor of sitting back and listening to your favorite station

Conclusion

HeatH p' " vides general =nd del ai led cir coil descriptions, semiconductor charts and suggested installation. Alter several hours ol operation Ihe frequency calibration drifted somewhat and a simple touch up of the frequency Himpot was in order.

I found only two real faults with the rig—both related to portable operation. The first concerns ihe power cord, If the rig it imended to oe laken mobile or for some other reason run off 12 V dc, there ¿s no way to disconnect the ac power cord. 1 think thai a detachable cord would save much aggravation

The second point concerns transporting ihe rig, A small handle on the rear panel would be ideal so that the radio can be carried with one hand without fear of drop ping iL I might add my Own *er> SOOn

Despite these minor drawbacks. I think that this receiver will be very popular. Someone will probably come up with an FM addition for ¡1, and perhaps a modification for ioohz readout capability

Heath has come up with another winner.

To recefve more information about Heathkd products, contact Heath Co.. Dept 150-395, Benton Harbor Mi 49022.

Greg Waller K3MGQ Birds bono PA

Continue reading here: Dick Smith Electronics Uhf Wattmeter

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