G8MNY  > TECH     30.11.21 08:00l 149 Lines 7621 Bytes #194 (0) @ WW
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Subj: Analyser SWIRES RESEARCH SA87
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Sent: 211130/0812Z @:GB7CIP.#32.GBR.EURO #:54421 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                              (New Jan 21)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

I bought this /P Cable TV spectrum analyser at a rally in 2000. It came with a
nice leather carrying case & charger, but a flat PB battery. I was made from
1988 & my one in 1991 in Basildon Essex. The 1st SA in the world to use a LCD
display was their earlier SA85 model!
                                                          Brill  Freq
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
       oAux 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴    (_) (  )      
 ()In                                                on          o ()쿎al
 High  oDC                    L C D                   off o sweep oIF  
                  D I S P L A Y   S C R E E N        쿫and o  (  )      
       oLED                                           pk  o      o      IF
 ()In      읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴              (_) 쿒ain
 Low                                                      Y(_) X(_)      
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
                                                                    Phones

It came with no information, so a lot or reverse engineering done to make a
full set of diagrams. But I did have a little success with an information
advert sheet from the maker & some history.

FEATURES
Freq   : 2 bands 5MHz-450MHz & 450-910MHz (External mixer/osc to 1750MHz)
Input1 : 75 BNCs up to 77dBuV (17dBmV) (Actually 20dB Better) 
Input2 : 75 BNCs 30dB attenuated, to 117dBuV (47dBmV) (Actually 20dB Better)
IF Gain: 10x 3dB steps
IF B/W : 300kHz, added a 30kHz narrow filter option
Cal    : 75 BNC 50MHz @ 5mV terminated, 74dBuV (14dBmV)
Sweep  : Around 4 per sec, gives start & end frequencies
Y      : Cursor On floor (my mod) changes Y scale to 5dB/Div
Y      : Off floor scale is 3dB/Div & reads out to +/- 0.2dB, 0.1uV
Pk hold: Shows the peak added up over time
X      : Cursor line gives frequency readout @ its position
X      : Cursor on LHS stops sweep, & draws level line, & H/P can be used
Phones : I added AM Rx opamp driving 3.5mm jack, used when sweep stopped
Display: LCD, added 5 x 10 graticule to estimate the display
AUX    : Powers down converter & adjusts Freq display to 1750MHz max

TESTING
Other than an expired small 12V Pb battery it all worked.

INSIDE
Is a double conversion RF module, 10.7MHz IF Module & calibrator, Control PCB
with my piggy backed mods board, Screen Display PCB,LCD, & Controls, DC SMPSU &
battery on the top. All inter-connected with plug in lose wire leads (no frail
ribbons).
旼컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컫컴컴컴
                                        Xtal         
            Set                      Set Freq        
            Temp    C O N T R O L                    
                                                     
                                     Z80 CPU     RF   Underside
  Set                  P C B                         
 Floor                        Options EPROM     Unit  View
                                 SW                  
  IF                                                 
                                                      Topside has
 UNIT 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴       SMPSU & battery
       Controls      LCD Screen & Driver PCB          in the middle
읕쩟컴컨컫컫컴쩟컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컨컴쩟컴 & Set IF Gain.
  잎     읕  잎                                    잎
 Cal                                               Input

SCHEMATIC
                 旼컴컴컴컴
Cal o)컴컴컴컴컴캑50MHz Osc                                 旼컴커
                 읕컴컴컴컴                             +25V    쳐Charge DC
Bandwidth>컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴  +16V SM 
Gain>컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커          +5V    쳐12V Battery
      /Tally dB                      Tally dB/          -8V PS 
Low o)컴컴컴컴                                            읕컴켸
Inputs旼컴컴  旼컴커 旼컴컴컴컴커 旼컴커 旼컨컴 旼컨컴컴 旼컴컴컴커
Hi  o)퀮tten쳐좔퀾ix1쳐951MHz IF 쳐퀾ix2쳐퀮tten쳐10.7 IF쳐퀽OG IF  첼
      읕컴컴   읕쩡켸 읕컴컴컴컴켸 읕컫켸 읕컴컴 쿑ilters 쿏etector납
        旼컴컴컴컴좔 旼컴컴왯컴컴커 旼좔컴커      읕컴컴컴 읕컴컴컴켸
Freq>컴캑Osc  951 - 쳐 Pre 납 Pre 쳐 Osc                            
Band>컴캑1/2 1872MHz 쿞cale납Scale 940MHz                          
        읕컴컴컴컴컴 읕컫컴牡컴쩡켸 읕컫컴켸                          
       旼컴컴컴컴커 旼컴컨컴컴컴좔컴컴컴좔                            
Brill>캑64 x 25ch     Counter     PLL   쳐<Tally dBs                 
       쿗CD Screen쳐퀱ata  CONTROL PCB    쳐컴컴컴컴컴컴컴컴컴쩡컴컴컴켸
       읕컴컴컴컴켸 읓컫컴쩡컴컴컴컫컴컴컴                   
Y >컴컴컴컴컴컴컴컴컴     旼컴컴좔컴컴커             旼컴컴좔컴커
Cursors                    8MHz Ref Osc             쿌M H/P Amp
X >컴컴컴컴컴컴컴컴컴컴    읕컴컴컴컴컴켸             읕컴컴쩡컴켸
AUX>컴컴컴컴컴컴컴컴컴컴컴                                   
Phones o컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴

Understanding the internals does help you use gear better!

MODIFICATIONS
1/ Change Pb battery for a 10x 500mA Nicad pack. Adjusted charging shutoff
2/ Added charger plug top status indicators
3/ Added switched narrow 30kHz filter, with sweep width reduction
4/ LCD Brill, range reduced so display not lost
5/ Added another 930MHz IF image trap
6/ Vertical range increased from 18dB to 30dB when Y cursor at bottom
7/ Made graticule for 5/3dB per div indication
8/ Added Sweep stop, with X cursor at LHS
9/ Added H/P amp & 3.5mm socket for AM Rx
10/ Modified Eprom data to remove annoying error message on over scan
11/ Added LCD front panel foil screening to reduce aerial QRM pick up
12/ Made Down converter to see & read to 1750MHz with 900MHz free running osc

IN USE
This /P Spectrum Analyser with no pick up leads, has the advantage it is easily
used to identify QRM sources, to show where they are. With a telescopic aerial
or clip on ferrite pickup one can identify leads that need attention & actually
measure any improvement.

The peak hold can be used to log the occasional QRM source & identify its level
& frequency.

In aerial testing the accurate 0.2dB readout can be used for comparing aerials
measuring gain etc. I use a Scanmaster SP-25 gasfet pre-amp too.

With my VHF pulse tester or a high-level noise source, filter can be tuned up,
like a tracking generator.
    
MATCHING
Although the 75 impedance may be a nuisance. However a simple 2 resistor
impedance change 5dB attenuator using a 42 in series & 91 across the 50 port
will match correctly (non inductive Rs).

50 o)컴쩡42컴>75          50 o)컴컴컴왯컴>75
       91             OR         ())))))           5x5=25, x2=50
     읕컨컴컴컴                  읕좔컴컴컴켸 1dB??   6x6=36, x2=72
        5dB                     Broadband ferrite beed

Or use a 5-6 turn ferrite bead auto-transformer.


Further reading;-
Also see my Tech buls on "Plug Top PS charge indicator", "Spectrum Harmonic
Demo circuit", "A Versatile Pulse Tester", "Clip on QRM Probe". "Spectrum
Analyser mods 88-89", "Analyser Takeda Riken TR4122B", "Power Line Telecomm QRM
"SSB Demo circuit", "Marconi 2019A Sig Gen", "FeelTeck Dual DDS Osc FY6600-60M"
& "RF Directional Coupler".


Why don't U send an interesting bul?

73 de John G8MNY @ GB7CIP


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