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G8MNY > TECH 19.12.24 08:23z 133 Lines 6617 Bytes #178 (0) @ WW
BID : 22225_GB7CIP
Read: GUEST
Subj: Marconi 2019A Sig Gen
Path: SR1BSZ<IW0QNL<IZ3LSV<DB0ERF<DK0WUE<DK0WUE<VK5RSV<VK5LEX<VE3KPG<GB7CIP
Sent: 241219/0818Z @:GB7CIP.#32.GBR.EURO #:22225 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Corrections Nov 19)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I acquired this old large 19" 3U rack unit in 2015, it is a digital entry
controlled PLL signal generator. The very similar 2018 model only does half the
frequency.
Frequency Modulation Level
___________________________________________________________
³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³
³ ³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄ¿ ³ ³Freq Cal
³ ³ ³ 1040.0000 MHz ³ ³ 75.0 kHz ³ ³ -127 dBm ³ ³ ³<side hole
³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÙ ³ ³
Mod Fr³ ³[]::: [] [][] [][][] [] [][] [] ³ ³
Ex ALC³ ³[] step [][] [][][] [] [][] fun2 (ú) ³ ³AF out
³ ³ [][] [][][] [] [][] ³ ³
On/Off³ ³ o (ú).(ú) [][] [][][] [] [][] ( o ) ³ ³RF out
³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³
~~~~~ÜÜÜÜ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ÜÜÜÜ~~~~~
Ex mod Parm Data Unit Disable
FAULTS
1/ Its front panel was falling off, a few screws sorted that, but I had to also
replace missing side cheek strips (no front handles) & provided a mains lead &
test lead. It seems to work OK, & I was able to fully test it.
2/ The 6 fixed AF Osc frequencies were all a bit low in Frequency, so I changed
the 2 Wayne bridge Osc's 10nF Cs for 9.75nF as I had some, spot on now.
3/ FM Deviation calibration using 1st Bessel null @ 2.405kHz Dev & 1kHz was out
of cal range, so I added a tweak R, feeding the preset. (See calibration below)
But exact calibration was variable especially when cold "by many times" the
wrong level! With aid of a down loaded .pdf service manual, this variability
1st proved to the AB2 PCB relays & ops amp for FM mod high level AF
attenuators. On a 2nd look, at it it seemed to be R1 50R link through in the
Osc Board, but that was not it either! Then on the 3rd look, I found a nickel
(gold used for RF) AF SMA plug lead had a poor braid earth connection, that was
used as the relay atten reference earth. (Modulation board has software
controlled digital attenuators too). Some contact cleaner & a retighten sorted
it OK, so I now have an accurate reliable calibrated FM signal source at last.
4/ External FM Modulation was also not flat < 20Hz as the PLL gave a +3dB lift
@ 7Hz. (common issue with PLL controlled Osc fighting the Modulation)
+3dB_³ _
0dB_³ / \_______________________________
-3dB_³ / before mod \
-6dB_³/ \ So added LF cut compensation
of a 2u2 in series with
0dB_³ __________________________________ 10K R91 on the mod PCB.
-3dB_³ / after cap \ Now quite flat 6Hz-100kHz @-3dB.
-6dB_³/ \
ÀÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄ
3 10 30 100 300 1k 3k 10k 30k 100k Hz
5/ Any mains spikes/breaks cause the signal generator to crash. A CPU reset
occurs when the 5V drops to 4.5V (to protect the memory from corruption!). So I
added 2x 4,700uF to the 5V rail's input +10V, to aid the main 15,000uF resivour
C to nearly double the bad mains OK "hang on in time".
NEW SPECIFICATION
Frequency : Range 80kHz (Usable from 30kHz) to 1040.0000MHz in 100Hz steps
PLL Frequency has 7.5 digit LCD readout
Mod AF : 300, 400, 500, 1k, 3k, & 6k Hz @ +/- 2%, for AM FM PM & AF output
Ext Mod : BNC, 6Hz-100kHz, Cal Level warning LEDs/ALC for level calibration
Ext FM Mod: 2nd Mod input allows pilot tones etc. to be added
Mod Level : AM 0-99%, FM 0-1MHz (10%) Dev, PM [0M] 0-999 Radian. 3 dig LCD
Distortion: AM <5%, >-30dBc higher order sidebands @ 99% mod.
AF Output : BNC, 100uV to 5V RMS. -77.8 to +16.2dBm max. 3.5 dig LCD readout
RF Output : N 50R. 0.1uV to 1V RMS, -127.0 to +13.0dBm max. (6dB less on AM)
Memories : Store & recall of 100 freq, 0-20 has full params, non volatile
Key Colour: Orange start data entry, Black Data, Grey Unit end. Blue 2nd mode
Accuracy : <1/10^7 after 5 min. Temperature controlled Xtal oven reference
In out Ref: Rear 10MHz (1MHz Programmable) BNC for ref Out/In
Spurious : Harmonics -30dBc, typically -50dBc, & spurii better than -65dBc
Protection: Accidental Tx RF input OK to 50W Max!
Power : 55W 230V Adjustable. IEC socket RT angle plug to stand up on end
Weight : 17kg.
CALIBRATION
Hole on RHS with rubber cover, is very accurate Ref Osc tweak with thin driver,
(inside on 2018). Inside the top cover there are PSU for voltages +24 +15 +5 &
-15V. Behind the front panel is the plug in Modulation PCB & its row of presets
(left to right) for:-
"Ext Gain, Ext ALC, Ext Threshold (hi/low leds), AF Level, PM, AM, & FM."
Marconi software, maps the AF Gain changes for the 4 FM oscillators at 82
frequencies points, to keep calibration reasonable. Similar mapped changes are
used for AM, Phase, & RF Levels.
OPERATION
Power up gives software version 003 for a few seconds, then default setting
1040MHz @ -127dBm, 0 mod. (Memory 10 for other power up parms, see user manual)
1/ Press Orange Freq key, enter freq, & end with Grey MHz/kHz/Hz key.
2/ Press Orange RF Level key, enter level, & end with Grey dBm/V/mV/uV key.
3/ Press Orange AM/FM/PM if needed, enter mod level & its Grey unit key.
4/ Select a Black Disable key, eg. RF/Int/Ex/AF/Mod off/on etc. as needed.
/_\ Delta, shows unit steps for the ^ up & v down keys. & allows changes.
2nd Function key, for additional set-ups see handbook. Any Orange key resets.
External key, can give error code ---15--- if no Ext Ref. Orange key resets.
USES
Although far more complex to use than my old Systron Donner Sig gen, it is
lighter, & lends itself for:- FM & AM demos on Ham training courses, etc. Rx
alignment & sensitivity tests, as it has a well screened RF output with 140dB
range in 0.01dB steps. Also its wide FM modulation of 1MHz deviation (>100MHz)
with up to 100kHz of External AF, is useful for accurate calibration of
broadcast deviation meters, measuring & compensating frequency response etc.
See my tech Buls on "Syston Donner Sig Gen", "FeelTeck Dual DDS Osc FY6600-60M"
"Analyser Takeda Riken TR4122B","RTT Comms Test Set", "198kHz Off Air Standard"
"Comparing Off Air Freq Standards", "Off Air Lock for Ref Osc" & "Scope RF
Trick".
Why don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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