OpenBCM V1.07b12 (Linux)

Packet Radio Mailbox

SR8BBS

[OBCM_Lublin]

 Login: GUEST





  
G8MNY  > TECH     27.11.21 09:51z 61 Lines 2540 Bytes #29 (0) @ WW
BID : 54209_GB7CIP
Subj: Spectrum Harmonic Demo circuit
Path: SR8BBS<SR1BSZ<IW0QNL<ON0AR<GB7CIP
Sent: 211127/0946Z @:GB7CIP.#32.GBR.EURO #:54209 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                              (Updated May 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Being involved with ham training, I have been doing all the technical demos
including AM & FM (Signal Generator) & this one for harmonics....

                                             ┌────────┐
                                          50ŕ│SPECTRUM│ ┌───────┐
                          Bypass           ┌─┤ADAPTOR ├─┤  X-Y  │
┌──────┐  ┌──────┐      ┌──────────┐       │ │0-90MHz ├─┤DISPLAY│
│RF SIG│  │DIODE │     o┘ ┌──────┐ │       │ └────────┘ └───────┘
│ 6MHz ├──┤PROBE ├──o─>o──┤ VIDEO│ └o      │┌─────────┐
│  1V  │  │INSERT│        │ WALL ├──o<─o───┴┤  SCOPE  │
└──────┘  └──────┘        │FILTER│         T│WAVEFOREM│
                          └──────┘          └─────────┘

I cheated with the use of a diode probe (series schotky diode for UHF) insert
to produce a poor signal when the sig gen is set to 1V output. This caused the
RF sine wave is bent enough to see the harmonics on 6MHz on a scope (>20MHz) & 
the diode output is terminated into 50ŕ by the spectrum analyser.

The filter I had is an 8 section M derrived video LPF & is 40dB down @ 8MHz,
but only 2dB down @ 6MHz. But any suitable filter will show the benefits of a
LPF after a harmonic rich source.

SPECTRUM DISPLAYS

              NO FILTER                                WITH FILTER
dB     f1  Rich harmonic spectrum              dB     f1
  0 ┤   │  f2                                   0 ┤    │  Cleaner
-10 ┤   │   |      f4                         -10 ┤    │  Spectrum
-20 ┤   │   │  f3   |      f6                 -20 ┤    │
-30 ┤   │   │   │   │  f5   |  f7  f8         -30 ┤    │
-40 ┤   │   │   │   │   |   │   .   |         -40 ┤    │
-50 ┤   │   │   │   │   │   │   │   │         -50 ┤    │    f2
-60 ┴───┴───┴───┴───┴───┴───┴───┴───┴─>F      -60 ┴────┴────┴──────────>F
        6  12  18  24  30  36  42  48MHz               6   12MHz
 

SCOPE DISPLAYS

        /''\        /''\                  /'`\        /'`\
       |    |      |    |                |    |      |    |
RF    _Ţ    Ů______Ţ    Ů____            Ţ    Ů      Ţ    Ů
                                        Ů      Ţ    Ů      Ţ  
                                               |    |
          Distorted RF              With Filter \../



See also my buls on "SSB Demo circuit", "Scope RF Trick", "Tuned Circuit Scope
Demo" & "Oscilloscopes".
 

Why don't U send an interesting bul?

73 de John G8MNY @ GB7CIP


Read previous mail | Read next mail


 29.11.2021 02:53:22zGo back Go up