G8MNY  > TECH     30.11.21 08:00l 149 Lines 7621 Bytes #194 (0) @ WW
BID : 54421_GB7CIP
Sent: 211130/0812Z @:GB7CIP.#32.GBR.EURO #:54421 [Caterham Surrey GBR]

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
       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(_)      

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.

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

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

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
            Set                      Set Freq        
            Temp    C O N T R O L                    
                                     Z80 CPU     RF   Underside
  Set                  P C B                         
 Floor                        Options EPROM     Unit  View
                                                      Topside has
 UNIT 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴       SMPSU & battery
       Controls      LCD Screen & Driver PCB          in the middle
읕쩟컴컨컫컫컴쩟컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컨컴쩟컴 & Set IF Gain.
  잎     읕  잎                                    잎
 Cal                                               Input

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
Phones o컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴

Understanding the internals does help you use gear better!

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

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.
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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