Login: GUEST @ JH4XSY.14.JNET1.JPN.AS [Tsuchiura]
home | newest check | boards | help index | log | ps | userlogin | send sysop | slog | status forward | bcm news | users | version | remove cookie
G8MNY > TECH 09.11.25 18:24l 546 Lines 28157 Bytes #10 (0) @ WW
BID : 44607_GB7CIP
Subj: Spectrum Analyser mods 88-89
Path: JH4XSY<N3HYM<CX2SA<ED1ZAC<GB7CIP
Sent: 251109/0913Z @:GB7CIP.#32.GBR.EURO #:44607 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Sep 20)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here are 22 modifications I have done to this popular scope adaptor design that
was first published in the RSGB's Radcom Technical Topics Apr 1988.
This design used just 3 ICs, 4 regulators & 1 transistor. A MC3356 is the 1st
osc mixer and log IF (most of the 94 transistors in the IC are not used), a
MC602 (NE602) 2nd osc mixer, a TL084 quad op amp to do the sweep, and �12V 1A,
+5 and +6V 100mA regs. (in 1989 a similar mark 2 design and PCB kit was
published, with bells & whistles, very complex with loads of 741s and
calibrated switches).
LAYOUT
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾗﾄﾄﾄﾄﾄﾄｿOuter
ｳﾚﾙMainsﾀｿ ﾚﾄﾄﾄﾄﾄﾄﾄｿ Mains ｳBox My one was very neatly UGLY
ｳｳTransf-ｳ ｳ PSU ｳ ｳ constructed (not by me) with
ｳﾀｿormerﾚﾙ ｳ_______ｳ inner box ｳ double sided PCB made box and
ｳ ﾚﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂｿ ｳ aluminium folded U top cover.
ｳ ｳｳ ﾚﾄｿ r2 ﾚﾄﾄｿ ｳ Op ﾚﾄｿ ｳｳ ｳ
ｳ ｳｳ ｳMｳ ｳ()ｳ ｳAmpsｳ ｳ ｳｳ ｳ r1=78L06 Then again with the RF bits
ｳ ｳｳ ｳCｳ ｳ()ｳ ｳ ﾀﾄﾙ ｳｳ ｳ r2=78L05 in a 2nd bolted in PCB
ｳ ｳｳ ﾀﾄﾙL2 ｳ()ｳ ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴｳ ｳ box with individual screen
ｳ ｳｳ L ﾀﾄﾄﾙ ｳ ﾚﾄｿ r1 ｳｳ ｳ partitions and RF feed through
ｳ ｳﾃﾄﾄﾄﾄﾄﾄｿ IF1 ｳ ﾀﾄﾙ()2ndｳｳ ｳ caps for lines in & out,
ｳ ｳｳL1 ｳIFamp ｳIF2 Mix ｳｳ ｳ an RF tight fitting fingered
ｳ ﾀﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾙ ｳ aluminium lid.
ｳ ________ ____ Sweep ｳ
ｳ ｳ Attn ｳ ｳPot ｳ ﾚﾄﾄｿ ﾚﾄｿ ｳ
ﾀﾄﾁﾒuﾄuﾄuﾁﾄﾒﾄﾁﾄﾂﾂﾄﾁﾄﾒﾄﾁﾂﾂﾁﾄﾄﾁ=ﾁﾄﾙ
RF X ﾀﾙ Y ﾀﾙ on/off
MY IMPROVED DESIGN
Input LPF Protect HF Trim 1st 1st IF 2nd 2nd IF IF Filter
Atten 0-90 Clip EQ Bias Mixer 145 Mixer 10.7 Amp 10.7
ﾚﾄﾄﾄｿ ﾚﾄﾄﾄｿ ﾚﾄﾄﾄｿ ﾚﾄﾄﾄｿ V ﾚﾄﾄﾄｿ ﾚﾄﾄﾄｿ ﾚﾄﾄﾄｿ ﾚﾄﾄﾄｿ ﾚﾄﾄﾄｿ ﾚﾄﾄﾄｿ
o)ﾄｴ ｳ ﾃﾄﾄｴ~~\ﾃﾄﾄｴ ^vﾃﾄﾄｴ-ﾄ'ﾃﾄﾄﾁﾄﾄｴ< >ﾃﾄﾄｴ_ﾛ_ﾃﾄﾄｴ< >ﾃﾄﾄｴ_ｳ_ﾃﾄﾄｴｳ> ﾃﾄﾄｴ_ｳ_ﾃﾄｿ
ﾀﾄﾄﾄﾙ ﾀﾄﾂﾄﾙ ﾀﾄﾄﾄﾙ ﾀﾄﾄﾄﾙ ﾀﾄﾂﾄﾙ ﾀﾄﾄﾄﾙ ﾀﾄﾂﾄﾙ ﾀﾄﾄﾄﾙ ﾀﾄﾄﾄﾙ ﾀﾄﾄﾄﾙ ｳ
ﾚﾄﾄﾄｿ ｳ ﾚﾄﾁﾄｿ 1.5MHz ﾚﾄﾁﾄｿ 50kHz 50kHz ｳ
/oﾄﾄﾄｴﾁﾁﾁﾃﾄ>ﾙ 145-235ｳOSCｳ ｳOSCｳ terminated for shape ｳ
ﾀﾄﾄﾄﾙMarkers MHz ﾀﾄﾂﾄﾙ ﾀﾄﾄﾄﾙ ｳ
Vernier ﾚﾄﾄﾄｿ ｳSweep 134.3MHz ｳ
Frequency<ﾄﾄﾄﾂﾄﾄ>ﾄﾂﾄﾄｴｳ> ﾃﾄﾄﾂﾄﾄﾄ>ﾄﾄﾄﾙ \ｳ/
Pot ｳ ｳ ﾀﾄﾄﾄﾙ ｳ ｳ
ｳ ｳ ﾚﾄﾄﾄｿ ｳCorrected ｳ
ﾚﾄﾄRamp ｳ ﾀﾄﾄｴ_./ﾃﾄﾄﾙSweep ｳ
ｳ Sweep<ﾄﾙ ﾀﾄﾄﾄﾙNFB Filter ｳ
ｳ Pot Log Amp & Detector 10.7 ｳ
X o)ｴ ﾚﾄﾄﾄｿ ﾚﾄﾄﾄﾄｿ ﾚﾄﾄﾄｿ ﾂ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄｿ ｳ
S ﾀﾄﾄｴ <ｳﾃﾄﾄｴ <ｳ ﾃﾄﾄﾄﾄﾄﾄﾄﾄｴｳ> ﾃﾄｴ< Sync ｳﾚ<ﾃﾂ<ﾃﾂ<ﾃﾂ<ﾃﾂ<ｳﾃﾄﾄﾄｴ_ｺ_ﾃﾄﾄﾄﾙ
C ﾀﾄﾄﾄﾙ ｳRampﾃﾄﾄ<50Hz ﾀﾄﾄﾄﾙ ｳ clamp ｳ 5 Detectors ｳ ﾀﾄﾄﾄﾙ
O Buffer ｳOsc ﾃﾄｴﾃﾄｿ Flyback ｳ ﾀﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾙ 300kHz
P ﾀﾄﾄﾄﾄﾙ ﾁ Amp ｳ 10kHz ｳsum Spurious
E ﾚﾄﾄﾄｿ1kHz ｳ ﾚﾄﾄﾄｿ ﾚﾄﾄﾄｿ ｳ Wall Filter
Y o)ﾄﾄﾄｴ~~\ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ<ﾄﾄﾄﾁﾄﾄｴ_/~ﾃﾄﾄﾄｴ~~\ﾃﾄﾄﾄｴ
o\ ﾀﾄﾂﾄﾙLP ﾀﾄﾄﾄﾙ ﾀﾄﾄﾄﾙ Y Cal
LPF ﾀﾄﾄﾄﾙVideo Detector S Video ﾁ
Switch Filter Correction Filter
After modifications here is the upgraded Specification:-
Frequency Range 200kHz-90MHz
Level flatness 200kHz-70MHz -3dB, 80 -6dB, 90-16dB
BNC 50R input @ up to +20dBm (0.5W Max with all atten in),
70dB of input Attenuators 10, 20, & 40dB.
IF bandwidth 50kHz @ -20dB
Video Bandwidth 10kHz or 1kHz @ -3dB
Sensitivity +20dBuV (10uV) for 10dB/Noise
1st IC protected by clipper (not attenuator)
70dB of vertical Y log scale. (�2dB)
60dB mixer dynamic range before onset of mixer overload
BNC Y Scope output calibrated to 100mV/10dB, with negative flyback syncs.
Sweep rate 50Hz flyback locked to supply (�1Hz)
BNC X scope Ramp Output 20V P-P
5MHz RF Markers up to 90MHz
Vernier Dial Frequency readout, Accuracy � 1MHz
No display of lower image sideband (below 0Hz)
210-254V 50-60Hz Mains Operation 10W.
CIRCUIT MODIFICATIONS:
INPUT
1/ There are 3 attenuators, the 10 & 20dB are accurately achievable with 1
double pole changeover switches separated by PCB screens. But the 40dB one is
not so easy, and needs some attention to detail, and an additional screening
plate between the connections to achieve it over the frequency range.
Note the 2K4 & 51R are E24 series, but 2K2, and pairs of 100R (* or 3x 150)
work quite well and may give higher dissipation if 500mW is put in. All Rs
small types and NOT WIRE WOUND! Very short leads are used on the 3 small
switches.
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ｳ ﾚﾄﾄﾄﾄ2K4ﾄﾄﾄﾄｿ ｳ ｳ ｳ
ｳ ｳ ﾚﾄﾄﾄﾄﾄｿ ｳ ｳ ﾚﾄﾄﾄﾄﾄﾄﾄﾄｿ ｳ ﾚﾄﾄﾄﾄﾄﾄﾄｿ ｳ__ 50R Coax
BNC o)ﾄﾁo/ | \oﾁﾄﾄﾄo/ \oﾄﾄo/ \oﾄ)__ to filter
Input ｳ ﾄｿ | ﾚﾄ ｳ ﾀﾂﾄ270Rﾄﾂﾙ ｳ ﾀﾂﾄ68Rﾄﾂﾙ ｳ
50R ｳ * 51R | 51R ｳ 68R 68R ｳ 100R 100R ｳ
ﾀﾄﾄﾄﾄﾄﾁﾄﾁﾄﾁﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾙ
40dB 20dB 10dB
I found that the losses reduced by the odd dB at higher frequencies, this is
due to.. switch crosstalk capacitance, series R capacitance or low R inductance
earth inductance etc.
2/ At the input to the low pass filter, add a 5MHz marker clock oscillator IC
mounted right beside the filter L. The output is loosely coupled by stray
capacitance with its short 1 cm lead for accurate frequency markers.
(The mk 2 SA has a marker already). The L1 is 5 turns wide spaced 5mm dia.
DC is via a push button.
Markers 14ﾚﾄﾄﾄﾄﾄｿ9 stray pick up protection
ﾄo\ﾄﾂﾄ470Rﾄﾂﾄﾄﾄﾂﾄﾄｴ 5MHzﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ L1 clipper HF lift Pin 20
+12V ｳ ｳ ｳ ｳ OSC ｳ from >ﾂﾄ(((()ﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄｴﾃﾄﾄ(((()ﾄﾄﾂﾄﾄ> MC3356
=== _ｳ_ === ｳ IC ｳ atten ﾃﾄﾄｴﾃﾄﾄﾄｴ _ｳ_ _ｳ_ ｳ 10n 8turns ｳ/\ 250�
u1ｳ 5V/_\' ｳu1ﾀﾂﾄﾄﾄﾂﾙ === 15p === \_/ /_\ 62R 6mm === I/P Z
ｳ ｳ ｳ ｳ7 1ｳ 56p ｳ 56pｳ ｳ ｳ ｳ /ｳ 20p
ﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄ
CLOCK IC LPF 2x1N4148 Term
3/ Change the low pass filter termination to 62R as it is in parallel with 250R
IC input Z. My filter is 3dB down @ 90MHz with about 30dB rejection above that.
4/ Add RF clipping diodes across termination R to protect IC1. These do not
conduct at all, for on screen signal levels. But do stop you blowing up the IC
with silly signals (e.g. from a handheld), but the input attenuator is
unprotected!
5/ The conditioned signals from the attenuator and VHF wall filter is fed
through a L & C trimmer for best HF level @ 70MHz into the 250R input Z of the
mixer IC1 (1st half of MC3356 IC). The IC is not designed for the Local Osc @
so high frequency, so there is some drop off of sensitivity @ 80MHz without
this tweak.
1st MIXER in MC3356.
A 2:1 step up ferrite transformer and no termination resistor will give 6dB
more gain, but no transformer is flat over 0.5 - 90MHz range so this is not
used. The mixer has a gain of about 5dB.
The osc provides 2 out of phase outputs (one with no RF!) that are buffered to
drive the Gilbert mixer cell (unbalanced), which has one RF input and 1 output.
Tuned cct OSC BUFFERS MIXER CELL
+12Vﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄ 4oﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄ +12V
=== ) L2 ｳ ｳ/ ｳ ｳ ｳ ｳ 4.3uH )
10n_ｳ_ ﾃﾄﾄﾄﾄﾄ 3oﾄﾂﾄﾄﾄ)ﾄ10Kﾄｴ ｳ ｳ ｳ IF ｳ L3 ) 1n
ﾚﾄﾄﾄｴ \ｳ ｳ ｳ\e ｳ/ ｳ ﾚﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄ)ﾄo5 ﾄﾄﾄﾁﾄｴﾃﾄ>
=== ｳ ﾃﾄﾁﾄ10Kﾄﾄﾄ)ﾄｴ ｳ ｳ ｳ ｳ ｳ to 145MHz
/_\ === 2p2 e/ｳ ｳ ｳ\e ｳ/ \ｳ ｳ/ \ｳ 50K IF Filter
Sweep ｳ ﾃﾄﾄﾄﾄﾄ 2oﾄｴ ｳ ﾃﾄｴ ﾃﾄﾂﾄｴ ﾃﾄｿ ｳ
>ﾄ10Kﾄｴ ｳ ｳ ｳ ｳ ｳ\e e/ｳ ｳ ｳ\e e/ｳ ｳ ｳ
ｳ ｳ ｳ ｳ ｳ ﾀﾄﾄﾂﾙ ｳ ﾀﾂﾄﾄﾙ ｳ ｳ
ｳ === 5p ｳ ﾃﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾙ ｳ ｳ ｳ
1n === ｳ ｳ ｳ ﾃﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾙ ｳ
ｳ ｳ RF in ｳ ｳ ｳ ｳ/ \ｳ ｳ
From>ﾄ)ﾄﾄﾄ)ﾄﾄﾂﾄ 20oﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄ)ﾄﾄﾂﾄｴ ﾃﾄﾂﾄ10Kﾄｴ
LPF ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ\e e/ｳ ｳ ｳ
ｳ ｳ ｳ ｳ ｳ ｳ ｳ ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄｴ ｳ ｳ
ｳ ｳ ｳ ｳ ｳ ｳ ﾀﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄ)ﾄ10Kﾄｴ
ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ _ｳ_
ｳ ｳ 1M 50K 50K 50K 330R 330R === \_/
ｳ ｳ Preset ｳ ｳ ｳ ｳ ｳ ｳ20p _ｳ_
ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ \_/
0V ﾄﾄﾁﾄﾄﾄﾁﾄﾄﾁﾄ 1oﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾄﾙ
L2 is a spread out coil 5 turns 5mm dia. The 12V is well decoupled with 10n @
L3. The original Varicap was a MV209.
N.B. never accidentally put earth on pin 2 or 3, that will destroy the OSC NPN!
6/ To get the last drop of balance out the 1st mixer, I found a 1M preset from
RF input to ground could give a slight improvement in balance and reduce a 2nd
harmonic of a pure RF signal by 2dB.
dB 0Hz
+70ｴｳ
+60ｴｳ .Fo If the balance is the other
+50ｴｳ ^ ｳ way, try the pot to +12V.
+40ｴｳ | ｳ Adjust 1M
+30ｴｺ ~60dB ｳ for Min Use a well filtered Osc (2-30MHz)
+20ｴｺ | ｺ \|/ so the 2nd harmonic > -60dBc
+10ｴｺ v ｺ 2Fo Noise
0ｴﾐﾄﾄﾄﾄﾄﾄﾄﾄﾟﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄ Floor
7/ The varicap tuned first local VHF oscillator's range has extended to tune
from 145MHz to 235MHz by adding further UHF Varicaps across the initial one and
stretching/reducing the osc L2. This may depend on the varicap used & stray C.
8/ The local oscillator coil is adjusted to give 0Hz line (e.g. osc = 145MHz)
when the FREQUENCY control vernier is set to 0 (mechanically near the -12V end
of the pot, so that tuning sweep voltage after the amp is near to +12V). This
also stops the unwanted image side of the 0Hz from being displayed & causing
confusion. The 22uF bipolar cap removes any scratchyness in the freq pot.
+12Vﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
FREQ<ﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄ>Tuning ｳ 0Hz
10K POT ｳ DC ｳ ｳ
ｳ ===22u ｳ No ｳ 5MHz
80MHz CAL ｳBipolar ｳInvertedｳ ｳ Markers
5K PRESET _ｳ_ ｳDisplay ｺ | ｳ ｳ
-12Vﾄﾄﾄｴ<ﾃﾄﾄﾄﾄﾙ ｳ \ｳ/ ｺ ｳ ｳ ｳ ｳ ｳ
Thermal ｳ________ｺ_ｳ_ｳ_ｳ_ｳ_ｳ_
compensation. (See 21/ & 22/)
1st IF FILTER
9/ Mine used a standard 50R 2M three pole TOKO 144-146MHz filter, (the original
article said to build your own). The TOKO one can be modified from a bandwidth
of about 3MHz (-10dB) with 3 peaks, to a single peak 1.5MHz wide, by adding 2
small metal shielding strips (6mm x 8mm) to cover the 2 apertures between the 3
coil sections, BUT this is fiddly to do!
Underside view After mod
ﾚﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄｿ ﾚﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄｿ
ｳ( ) ( ) ( )ｳ ｳ( )ｳ( )ｳ( )ｳ
ﾀﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾙ ﾀﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾙ
To see the 1st IF response on its own on the display, to tune it up, temporally
remove connections to the 2nd IF filter and bypass it with a bridging 1nF cap
and feed a carrier in (marker).
_ _ _ ..
ｳ / \./ \./ \ ｳ / \
ｳ | | ｳ | |
ｳ ｳ ｳ ｳ ｳ ｳ
ｳ | | ｳ | |
ｳ_./ 3MHz \._ ｳ____./ 1.5MHz \.__
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ
Once the 1st IF's bandwidth is reduced then the number of signals reaching the
2nd mixer is greatly reduced and hence this reduces the amount of unwanted
distortions and close in mixing products being displayed.
2nd MIXER.
This uses a NE602 osc and a balanced Gilbert cell mixer (used unbalanced) with
similar internal circuit to that of the MC3356 RF part, it runs on its own +6V
regulator and RF decoupled. Mixer gain is about 17dB.
+6Vﾄﾂﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄｿ * see /11 for value
=== 8t ｳ,/\ ｳ *ｳ === 10n
1n_ｳ_ 5mm (| ｳ8 430R _ｳ_
/(| 6ﾚﾄﾄﾄﾄﾁﾄﾄﾄﾄｿ ｳ
134.3MHzﾃﾄﾄﾄﾄﾄｴ ｳ4 ｳ to 10.7MHz
3p9 === 7ｳ NE ﾃﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄ>ceramic
145MHz ﾃﾄﾄﾄﾄﾄｴ 602 ｳ filter
IF >ﾄﾄﾄｴﾃﾄﾄﾄ)ﾄﾄﾄﾄﾄｴ ｳ N.B. as with 1st osc
1n ｳ 1ﾀﾂﾄﾄﾄﾂﾄﾄﾄﾂﾙ an accidental earth
=== ｳ2 ｳ3 ｳ5 on pin 6 or 7 will
6p8 ｳ 1n=== ｳ ===1n destroy the osc NPN.
ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄ
10/ The VHF oscillator in the 602 should be run on a lower frequency (core "in"
position) to the 1st IF, this is to reduce spurious images. e.g. 10.7MHz 2nd
IF needs 134.3MHz, (or a 6MHz IF needs 139MHz). Due to the ferrite core this
osc is susceptible to changes in magnetic fields, so mains transformer flux can
be a problem for "zoomed in" stability!
2nd IF FILTER
11/ The 2nd mixer's output has in internal pull up of 1K5 to so get 330R source
impedance for the filter a 430R on pin 4 determines the 2nd IF filter source
impedance. (This is not applicable to the Mark 2 with narrow filter option.)
ｳ .-ﾄ-ﾄ-. ｳ .--. If the filters are deliberately
ｳ ﾞ ﾝ ｳ / \ mismatched then they can give
ｳ ﾝ COMMS ﾞ ｳ | | a better analyser friendly
ｳ | Filter | ｳ | | "rounded peak response" rather
ｳ_./ 50kHz \._ ｳ_./ \._ than the flat topped ringy
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ edges of communication filters.
Correctly terminated Mis Terminated
RINGY FILTER sweep friendly filter
To find the best values for your filters use small 1k presets to source and
terminate the filters to see this effect on the display of a carrier, find the
optimum value for best IF shape and then replace the presets with nearest fixed
values.
+12Vﾄﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
=== u1 ｳ IF ｳ
+6V _ｳ_ ｳ AMP 470R
2nd Pin 8<ﾄｴ 220K ﾚﾄﾄﾄﾄｴ
Mixer 430R ｳ ｳ/ ｳ
602 Pin 4>ﾄﾁﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄｴ T1 ｳ ﾚﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄ>Pin 7 To
Pin _ｳ_ _ｳ_ BFX90ｳ\e _ｳ_ _ｳ_ _ｳ_ _ｳ_ 330R MC3356
3 ﾚﾄﾄﾄﾄﾄｿ ｳ ﾚﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄｿ ﾃﾄﾄﾄﾄﾄﾄ>Pin 9 Log
ｳ 50kHzﾀﾄﾄﾄﾄﾄﾙ 100R ﾀﾄﾄﾄﾄﾄﾙ ﾀﾄﾄﾄﾄﾄﾙ ﾀﾄｴﾃﾄﾂﾄ>Pin 8 Detector
ｳ 10.7 ﾄﾄﾄﾂﾄﾄﾄ Preset ﾄﾄﾄﾂﾄﾄﾄ ﾄﾄﾄﾂﾄﾄﾄ ===
ﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄ>Pin 19
1st filter 2nd Wide filter
Adjust the 100R gain preset for the optimum noise floor that can just be seen.
12/ Adding an inter filter buffer stage using a single transistor T1 adds some
preset gain for setting the overall noise floor of the analyser, as well as
matching into a 2nd filter. This filter is terminated by the input load on the
detector 330R. Two 50kHz 10.7MHz ceramic filters provide a reasonable
compromise of selectivity for sweeping 0-80MHz @ 50Hz without too much ringing
distorting and loss of the peaks levels (up to 10dB) while still looking good
in close "zoomed in" sweeps. However a 3rd filter was put in tandem with the
2nd filter to clean up poor filter skirt rejection of my particular narrow
filters @ 7MHz!
LOG DETECTOR
13/ The detector (S meter output) uses 5 IF amps & detectors (with limiters) to
obtain log response and it is quite accurate for over 40dB range. But ignoring
the slight overload in the mixers this range can be extended on the display, by
increasing the gain calibration preset (1K preset now 2K2), and then adding a
non linear correction attenuator with diodes D1 (Schotky/Ge) and D2 (Si) to
give 30% stretch @ the highest and lowest levels where the detector has lower
sensitivity.
Ge 1.0 ｴOutput from _.-'
MC3356 pin ﾚﾄｴ>ﾃﾄｿ Y to .9 ｴDetector .-'
LOG 14>ﾄﾂﾄﾄﾄｴ ﾃﾄﾄﾄﾄﾂﾄﾄﾄﾄ> scope .8 ｴ .'
DETECTOR ｳ ﾃﾄ10Kﾄｴ ｳ .7 ｴ .'
2n2ｳ 680R ｳ ｳ T2 .6 ｴ .' S
Video === ｳ 22K \ｳ Timebase .5 ｴ .' Correction
Filter ｳ 2K2 _ｳ_ ﾃﾄ<Sync/ .4 ｴ _.-'
ｳ Y CAL \_/Si e/ｳ Blanking .3 ｴ_.-'
Pin 11>ﾄﾄｴﾃﾄﾁﾄﾄﾄﾁﾄﾄﾂﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄ .2 ｴ
Lim out 1n _ｳ_ .1 ｴ Display
is RF 0v ﾅﾄﾂﾄﾄﾂﾄﾄﾂﾄﾄﾂﾄﾄﾂﾄﾄﾂﾄﾄﾂﾄﾄﾂ>output
grounded 0 10 20 30 40 50 60 70 dB
With this correction you can get good display linearity to 70dB. Easily tested
with input attenuator and a signal generator to see equal height 10dB steps.
14/ The sensitivity is set by the Y Calibration preset to give 100mV/10dB. A
2.2nF capacitor limits the Y video bandwidth to about 10kHz (50%), but having
hardly any degradation of pulse height at the widest sweep range.
VIDEO FILTER
15/ For some applications lower video bandwidth is needed to reduce noise, I
added a 33nF switched across the Y output incorporated with the above mod, to
give about 1kHz Y bandwidth (50%).
ﾄ10kﾄﾄﾄﾂﾄ>Y to
ｳ scope
o\ﾄｴﾃﾙ
_ｳ_ 33nF
It needs to be switchable as it causes the output to lie about the fine detail
with wide sweeps.
POWER SUPPLY
16/ The hot +12V regulator has been heatsinked, and the + rail input smoothing
capacitor increased from 680uF to 2m2. Transformer and rectifier pulse currents
wiring and layout have been kept away from the regulators as far as possible to
reduce supply hum ripple pickup.
Heatsink
4x 1N4001 +17V ﾚﾄﾄﾄﾄｿ
ﾚﾄﾄﾄﾂﾄｴ>ﾃﾄﾂﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄｴ7812ﾃﾄﾂﾄﾄﾄﾄﾄﾄ> +12V Much larger output
L >ﾄo/ oﾄﾂﾄｿ ｳ _ｳ_ _ｳ_ 2m2 ｳ+ ﾀﾄﾂﾄﾄﾙ+ｳ330u 200mA caps have been
100k )ｺ( /_\ /_\ 25v=== ｳ ===16v used to reduce
240V ｳ )ｺ(___ ｳ ___ ｳ ______ｳ____ｳ____ｳ______\ 0V the last remnants
NEON )ｺ( ｳ ｳ 680uｳ+ ｳ ｳ+ / of hum & noise.
ｳ )ｺ( ｳ ｳ 25v=== ｳ ===330u This is most
N >ﾄﾄﾄﾄﾄﾄﾁﾄﾙ ｳ ｳ ﾀﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄｴ ﾚﾄﾁﾄﾄｿ ｳ 16v important
ｳ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾂﾁﾄﾄｴ<ﾃﾄﾁﾄﾄﾄﾄｴ7912ﾃﾄﾁﾄﾄﾄﾄﾄ> -12V for close in
E >ﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾙ 14-0-14 ｳ -19V ﾀﾄﾄﾄﾄﾙ 20mA stability.
ﾀﾄ> 0V 0.3A ﾀﾄ>50Hz
The mains transformer has also been varnished to reduce acoustic hum and an
outer copper short circuit added to reduce magnetic fields that can affect the
2nd osc stability. The other 2 low power regulators +6V for 2nd osc, and +5V
for Log amp, are placed near those circuits for best noise/voltage error
rejection.
17/ A 50Hz synchronisation line is provided for ramp timebase locking. This is
important for close "zoomed in" stability of the sweep.
RAMP GENERATOR
In the simple mark 1 design, it uses 4 operational amplifiers IC3 (e.g. TL084)
that run on the �12V. The original circuit produced a symmetrical 500Hz ramp up
and down oscillator which was far too fast for wide sweeps and half the time
was wasted during the flyback. Mod 18/ solves this.
18/ IC3a forms a 50Hz ramp oscillator with the 100K & 12K in parallel during
flyback due to the diode D3, and a 1uF timing capacitor to give close to mains
frequency. Then a small injection of 50Hz from the mains transformer alters the
flyback time (D3, 12K & 1uF) to cause lock up to mains frequency. This method
ensures constant sweep MHz rate and the mains lock ensure a stable display even
with some sweep hum present when zoomed close in.
ﾄｿﾚﾄﾄﾄｿ
50Hz 12VAC >ﾄﾄ100Kﾄﾂﾄ12Kﾄﾂﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄｿ ﾀﾙ ﾀﾙ _
from bridge _ｳ_ ｳ 100k ｳ ﾚｿ _ｳ \____
MAINS D3 /_\ 100k ｳ ｳ ﾄﾙﾀﾄﾄ
LOCKED /ﾃﾄﾄﾄﾄﾄﾄﾄﾄｴ ｳ ﾃﾄﾄｴ\ ｳ - ﾚﾄﾄｴ>ﾃﾄﾂﾄ22kﾄ>Y Blanking
50Hz <ﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄ<'IC3b ｳ ｳ ｳ ｳ>ﾄﾁﾄﾄｴ\ ｳ ｳ Transistor
RAMP,. ｳ n47 `\ﾃﾄﾂﾄﾄｿ ﾃﾄﾄﾄﾄﾄﾁﾄﾄ)ﾄﾄｴ/' +ｳ `>ﾄﾄﾁﾄﾄ2k2ﾄｴ T2
,/ ｳ ﾃﾄｴﾃﾄﾄﾄﾄﾄﾄｴ ｳ ｳ ｳ IC3a ﾚﾄﾄｴ/' ｳ
,/ ｳ,/ ﾀﾄﾄﾄ10kﾄﾄﾄﾙ 1k2 ===1u 10k ｳ IC3d u1===
' ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄ
Buffer x9 ,/'ｳ,/'ｳ 50Hz Ramp Osc Sweep Settle Delay
19/ IC3d buffers and
inverts the banking dB 0Hz
pulse and it is +70ｴ ｳ | /|\ + 0.9V
lengthened with CR +60ｴ ｳ Sweep |
and a diode before it +50ｴ ｳ Centre 100mV
drives blanking +40ｴ ｳ | /10dB
transistor T2. This +30ｴ ｺ |
eliminates any sweep +20ｴ ｺ |
folding due to VHF osc +10ｴ ｺ Noise Floor \|/
sweep settling delay 0ｴ ﾚﾟﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ + 0.2V
with RF sweep filtering SYNCSｳ SWEEP ^ ｳ
to be masked. And the ﾄﾄﾄﾙ | ﾀﾄﾄﾄﾙ - 0V
banking also gives Scope^ Scope
the scope a 0V sync Trigger Flyback
pulse to lock to. < - - - - 20mS - - - - ->
20/ IC3c is the sweep correction amplifier, this amplifies the selected sweep
width together with the centre frequency DC, then corrects for VHF oscillator
varicap frequency control non linearity by pre-distorting the ramp waveform
with 5 gain changes using 4 diodes, D4-D6 & ZD2 zener.
-12V>ﾄ3K3ﾄﾄﾄﾂﾄﾄ2K2ﾄﾄ<+12V MHz Tune
10 Turn 390K 240ｴRamp _
Tune<ﾄ68Kｿ R1 230ｴInput _..--''~
Pot ﾃﾄﾄ27Kﾄﾄﾂﾄｴ<ﾃﾄｴ 220ｴ Five _.--'~ R4
ｳ 27K _ｳ_ 210ｴ Slopes _.-' R3
Ramp ｳ ﾚﾄｴ\ ｳ /_\ To VHF 200ｴ .-'
ｳ ｳ ｳ ｳ>ﾁﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄ>Osc 190ｴ .-' R2
Sweep ﾃﾄ)ﾄｴ/'IC3c ｳ Varicap 180ｴ .'
Pot<ﾄ68Kﾙ ｳ ｳ 2.7V 170ｴ .' R1
10k ｳ ﾃﾄｴ>ﾃﾄﾄﾂﾄｴ<ﾃﾄｿ 160ｴ ;
ｳ ｳ R2 47K ﾙ 15K 4K7 150ｴ: Varicap Volts (ref to +12V)
ﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾁ 140ﾅﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂ
R3 R4 +12 9 6 3 0 -3 -6 -9 -12
The R1-4 values used for the gain corrections are set up using the marker to
give even spacings on the display.
0Hz
ｳ
ｳ . Even spaced 5MHz markers
ｳ ｳ . ｳ | | . . .
ｺ ｳ ｳ ｳ ｳ ｳ | ｳ | ｳ | ｳ | ｳ | ｳ | ｳ
ｺ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ 90
_ｺ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_ｳ_
5 15 25 35 45 55 65 75 85 MHz
FREQUENCY CONTROL
21/
+12Vﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
FREQ<ﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄ>Tuning The multiturn vernier
10K POT ｳ DC centre frequency control
ｳ === 22uF has a 22uF bipolar
80MHz CAL ｳBipolar! capacitor to ground
5K PRESET _ｳ_ (or elect to +12V near the ICs)
-12Vﾄﾄｴ<ﾃﾄﾄﾄﾄﾄﾄﾙ //// to remove any pot scratchiness.
Thermal
compensation.
22/ A multiturn preset pot on the positive rail of the control is added to
calibrate 80MHz position on the vernier scale. A diode in series gives some
temperature drift compensation. Together with the correction circuit of IC3c
fairly accurate frequency readouts are possible on the vernier scale. 0-90MHz.
I N U S E
IMAGES
Other than the 0 Hz line, there is only one unwanted image @ 10.7MHz, it is at
a low level and its appearance depends on the IF gain setting. It is due to the
second IF detector being in the same IC as the RF input section!
dB 0Hz
+70ｴ ｳ
+60ｴ ｳ VHF images are all well
+50ｴ ｳ down due to the VHF LPF
+40ｴ ｺ & the chip sensitivity
+30ｴ ｺ cutting off as well as
+20ｴ ｺ the input filter & double
+10ｴ ｺ Noise screened box.
0ﾅﾄﾟﾄﾄﾄﾄﾄﾄ^ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ Floor
10.7MHz
OVERLOADS
These can be seen as higher levels of harmonics increasing at a greater rate
than the fundamental. e.g. a 10dB increase in level, causes the fundamental to
increase by 10dB (1 division), but the 2nd harmonic increases by 15 to 30dB!
dB 0Hz dB 0Hz
+70ｴｳ +70ｴｳ Fo
+60ｴｳ Fo +60ｴｳ ^ ｳ
+50ｴｳ /|\ ｳ +50ｴｳ | ｳ Mixer
+40ｴｳ | ｳ +40ｴｳ | ｳ Generated
+30ｴｺ <60dBｳ +30ｴｺ >60dBｳ Harmonics
+20ｴｺ | ｺ +20ｳｺ | ｺ 2Fo
+10ｴｺ v ｺ 2Fo 3Fo Noise +10ｴｺ v ｺ ｳ 3Fo
0ﾁﾟﾄﾄﾄﾄﾄﾄﾐﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ Floor 0ｴﾟﾄﾄﾄﾄﾄﾄﾟﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄ
Filtered Osc test Filtered Osc test
OVER LOADING 1st MIXER
They can also be detected as unwanted sidebands around the markers too.
dB dB
+70ｴ Signal +70ｴ
+60ｴ ｳ +60ｴ
+50ｴ ｳ +50ｴ
+40ｴ ｳ Marker +40ｴ
+30ｴ ｳ ｳ +30ｴ Base Noise Floor
+20ｴ SﾄM ｺ ｳ S+M +20ｳ Raised __
+10ｴ Mix ｺ ｳ Mix +10ｴ __..--""~~
0ｴﾄﾄﾁﾄﾄﾄﾄﾟﾄﾄﾄﾄﾐﾄﾄﾄﾄﾁﾄﾄﾄﾄ 0ｴﾄﾄ""~~
POSSIBLY OVER LOADING MIXER GROSS OVERLOAD
Other signs of overload is a raised noise floor.
CLOSE IN OVERLOADS
These are much the same as above, but occur when the 2nd mixer sees 2 large
signals passing through the 1st IF filter. So if the narrowing of that filter
has been done, strong signals will need to be closer than 1 MHz to suffer this
problem. (e.g. using the analyser closer than 1 MHz from 0 Hz reduces dynamic
range due to the increased noise floor from its' own 2 oscillators)
FILTER NOISE SIDEBANDS
dB With large carriers are looked
+70ｴ at close in, you will see noise
+60ｴ /~\ sidebands (phase noise) added
+50ｴ ｳ ｳ to the filter response, this is
+40ｴ ﾝ ﾞ normal for this sort of analyser.
+30ｴ ﾞ ﾝ
+20ｴ Sideband ﾜﾝ ﾞﾜ Sideband Lower frequency Y display filtering
+10ｴ Noise _ﾜﾛﾟ ﾟﾛﾜ_ Noise can mask this, but at the cost of
0ｴﾄﾄﾄﾄﾄﾍｼﾟﾟﾟ <50kHz> ﾟﾟﾟﾈﾍﾄﾄﾄﾄﾄﾄﾄ peak pulse height accuracy.
SWEEP NOISE
Some of this phase noise can be noisy sweep amps, as the S/N needed on the VHF
osc will be >120dB, e.g. 24V max sweep and < 24uV of noise! I have used active
sweep filtering on some analysers to overcome this failing where the sweep rate
is low and a CR filter after the last opamp does reduce the HF noise sent to
the oscillator.
ﾚﾄｴ>ﾃﾄｿ The diode direction (depends on circuit)
ｳ\ ｳ ｳ ensures the flyback charges up the cap
OP ｳ `>ﾄﾁﾄﾄRﾄﾄﾁﾂﾄﾄﾄﾄ>VHF OSC voltage quickly, so there is little cramping
amp ｳ/' === C at the start of the sweep.
ﾄﾄﾁﾄﾄ e.g. Xc = R (-3dB) @ 10x sweep freq.
See my tech buls "Spectrum Harmonic Demo circuit", "RF Directional Coupler",
"Analyser SWIRES RESEARCH SA87" & "Analyser Takeda Riken TR4122B".
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
前のメール | 次のメール