7/17/2019 A Miniature HF to VHF AM-FM Receiver Using the NE605

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BY

IRWIN

MATH, WA2NDM

MATH S NOTES

WHAT'S NEW AND HOW T USE

IT

A Miniature

HF

to

VWF

AMIFM Receiver Us ing the NE6 5

t seerns that every time we preserit a

circuit for a miniature receiver we get

lots of rnail, most of which is con-~pli-

tary an d indicates that this type of pro-

t "tickles a lot of fancies." I am

xactly why that is, but if that's

o spark homebre wing,

ngs that m ay be applicable to a ma-

portion of the hobby is, after all,

this mo nth we are pleased to pre-

The Signetics (now Phill ips) NE605 is

r m ixerilF amplif ier integrated

e used as the heart of a sim-

circuit to be described,

ip, will enable you to construct

and FM receiver that can

sed for local moriitoring or for casua l

le entry-level com-

ications receiver. Before proceeding,

ver, be aware of the fact that this is

edium -perform ance circuit, not the

F to 50 0 MH z for the front end is

sible, the noise figure is only

ly will not be received a s well (if at

) as with your H T or standard comm u-

low-noise tuned pre-amp ahead

he NE6 05 will obviously increase per-

but that will not be covered at

internal circuitry, limiting opera-

rna l local oscillatGr will be;equired for

t ime. However,

microprocessor-

igher frequency single-channel

imitations men tioned in mind , a very sim-

le receiv erth at may suit man y needs will

Fig.

1

is a schematic of the simple, sin-

AM receiver using

CQ

magazine

'

OpF

= 001

ceramic

L1

C1

resonate

t

desired

operating frequency

cerarnic filters

L2 CZ

esoriate at Vcc

55 KHz

below desired

operating frequency

Fig.

1 Simple HF to V HF AM/FM receiver.

necessary: the input, which will provide

sorne deg ree of selectivity, and the loca l

oscillator, which should operate at 455

kHz below the desired input frequency.

Choice for the absolute values for these

circuits will be left to the expe rimenter and

probably will be dedicated by what is in

the junk b ox. The two items labeled F L I

and FL2 are common, low-cost 455 kHz

ceram ic filters design ed for AM rad io use

and are readily available.

In operation, signals received by the

antenna are applied to the input of the

NE605. This input goes directly into an

internal mixer stage, which accounts for

the higher noise figure. Also a pplied to the

mixer is the lo cal oscillator o utpu t, the fre-

quency of which is determined by the set-

ting of L2-C 2. The difference be tween the

two is the IF frequency, 455 kHz, and the

two ceramic fi lters are u sed to provide a

narrow p ass-band IF amplif ier at that fre-

quen cy. You will note that the local oscil-

lator is tunable. If fixed frequency opera-

tion is desired, C2 and its parallel padding

capacitor can b e replaced by a crystal of

the appropriate frequency. L2 and the

,001 IF capacitor, however, must be left

in. If you use the variable-oscillator ap-

proach, be sure that C2 and its padding

2

CQ

August

998 Say

You

Saw

It n Q

7/17/2019 A Miniature HF to VHF AM-FM Receiver Using the NE605

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ke the tuning range too wide will result

ty. Keeping the range to 1-1.5%

The 270

p H

coil and 390 p F capacitor

o pins 10 and 11 form a quad-

ignal and provides recovered audio

7 is usually use dfo r a received

th me ter. As a result, its out-

o the incoming signal am plitude.

s output m akes a neat AM detec-

the AM a nd FM audio ou tputs

e are used to equalize

An LM386 au dio ampli-

e entire receiver operates from

ed from a 9 volt

is

tput level.

When building the circuit, take ca re to

ans short leads, keeping input and

ay from each other,

So-cal led dead-bug or

construct ion methods are f ine as

re careful. Overall results are

nt to a great degree on layou,t so

careful.

The com pleted receiver can be m ount-

ve the local oscilla-

equency may leakth roug h. This is the

Q that

tracks the local oscillator can reduce this

but that's some thing you will ha ve

play with. Regardless of what your

the NE605 is a chip worth

ith.

As a final note, we have not purposely

ed exact layouts or bills of mater-

whole point of building such a circuit

to cut an d try until you acheive results

8

1 East Arques Avenue, Su nny-

88-3409. Good luck and let

ow of your results.

73, Irwin, WA2NDM

It s a different kin d of ham m agazine.

Fun to read, interesting from cover to cover, written so you c an unders tand it. That s CQ. Read

by

over

90 000 people each mon th in 116 countries around the world.

It s mo re than just a maga zine. It s an institution.

I

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Say You Saw It In CQ

CIRCLE 71

ON

READER SERVICE C RD

August

998

CQ

5