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G8MNY  > TECH     19.10.19 09:45l 76 Lines 3949 Bytes #7 (0) @ WW
BID : 26399_GB7CIP
Read: GUEST
Subj: Spectrum IF Demo circuit
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 191019/0739Z @:GB7CIP.#32.GBR.EURO #:26399 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                (New Feb 10)
(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 for
the advanced course, this one shows "under", "critical" & "over" coupling
between 2 tuned circuits.

SETUP
                           ┌────────┐
┌──────┐  ┌────────┐50ŕ    │SPECTRUM│ ┌───────┐
│  RF  │  │ DOUBLE │Pickup │ANALYSER│ │       │
│ NOISE├──┤ TUNED  ├───────┤ADAPTOR ├─┤  X-Y  │
│SOURCE│  │XTAL SET│Single │0.4-2MHz├─┤DISPLAY│
└──────┘  └────────┘turn   └────────┘ └───────┘

I cheated with the use of my RF Noise Bridge as a noise source & my Crystal Set
with its 2 sliding coils on a ferrite rod, as the variable couple tuned
circuits.

Using a noise source instead of a spectrum analyser's tracking generator is not
ideal & the display is quite wobbly, but using a low display video bandwidth &
slow sweep rate (50Hz) helps.

DEMO 1                                               ┌─────────────────────┐
Single tuned circuit                                 │          _          │
┌──────┐ = = = = = = = = = = = = = = = =             │        /' '\        │
│  RF  ├─(((()┐_   long ferrite rod   ┌()──To        │       /     \       │
│ NOISE│      │/|                     └────Analyser  │      /       \      │
│SOURCE│     ===                                     │    ./         \.    │
└──┬───┘     /│                                      │-──~             ~──-│
 ──┴──────────┘                                      └─────────────────────┘
                                                    Shows broad tuned circuit

DEMO 2                                               ┌─────────────────────┐
Under coupled tuned circuits                         │          _          │
┌──────┐ = = = = = = = = = = = = = = = =             │         / \         │
│  RF  ├─(((()┐_              _┌(((()┐┌()──To        │        Ů   Ţ        │
│ NOISE│      │/|            |\│     │└────Analyser  │        Ţ   Ů        │
│SOURCE│     ===              ===    │               │       /     \       │
└──┬───┘     /│                │\    │               │   _.-~       ~-._   │
 ──┴──────────┘                └─────┘               └─────────────────────┘
                                                     Narrower & better skirt

DEMO 3                                               ┌─────────────────────┐
Over Coupled tuned circuits                          │      _       _      │
┌──────┐ = = = = = = = = = = = = = = = =             │     / \     / \     │
│  RF  ├─(((()┐_  ┌(((()┐┌()──To                     │    Ů   ~-.-~   Ţ    │
│ NOISE│      │/| │/|   │└────Analyser               │    Ţ           Ů    │
│SOURCE│     === ===    │                            │   /             \   │
└──┬───┘     /│  /│     │                            │.-~               ~-.│
 ──┴──────────┘   └─────┘                            └─────────────────────┘
                                                    Always wide & double hump

DEMO 4                                               ┌─────────────────────┐
Critical Coupled tuned circuits                      │                     │
┌──────┐ = = = = = = = = = = = = = = = =             │        /~──~\       │
│  RF  ├─(((()┐_      ┌(((()┐┌()──To                 │       Ů      Ţ      │
│ NOISE│      │/|     │/|   │└────Analyser           │       Ţ      Ů      │
│SOURCE│     ===     ===    │                        │      /        \     │
└──┬───┘     /│      /│     │                        │  _.-~          ~-._ │
 ──┴──────────┘       └─────┘                        └─────────────────────┘
                                                     Almost ideal square top



See also my TECH buls on "RF Noise Bridge for LF, MF, & HF", "A Quality Crystal
Set" & "Spectrum Analyser mods 88-89".


Why don't U send an interesting bul?

73 de John G8MNY @ GB7CIP


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