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G8MNY  > TECH     12.11.23 09:46z 248 Lines 12302 Bytes #7 (0) @ WW
BID : 60182_GB7CIP
Subj: RTT Comms Test Set, Cal & Use
Sent: 231112/0943Z @:GB7CIP.#32.GBR.EURO #:60182 [Caterham Surrey GBR]

By G8MNY                             (Update Dec 22)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Now it is all fully working properly, extensively modified (see previous bul) &
calibrated (see below), the "Radio Telephony Test Systems" test set was made in
Feltham UK in 1987-9, & although old, it can do quite a lot...
      /                                                           /|
     /                                                           / |
  /  |
  /___________________________________________________________/  |
 ޳Ŀ  |
 ޳ĿĿĿĿĿ  |
 ޳ \ AF   \SINAD 5 3 99 9 9 9 0 0  \MOD   \POWER  |
 ޳__\______\__________________________\______\ ___  |
o   _         _   Oven     _   _       Lock         _  Rx  |
_   (_)_______(_)          () (_)    o    ! ! !   (_)   _ |
AFo  _ ________    _           _      _     _        .-.     |
in@ (_)  o  o  (_)  (_)  ! !   =(_)   =(_)   (_)   o  ( o ) RF /
  CTCSS Lis Vol MOD     _    SIG GEN FREQ    _  _   _'-'_ in/
  1234   LS   12     ()   1 2 34 5 6 7   () () ()=() /

RF Input          N socket 50 Ohm 20dB Load atten. 1kW peak, 50W continuous
Power Meter       1,3,10,30,100,300W FSD, (RF detection for Counter & Rx mode)
Frequency Counter 9 digit 1Hz-540MHz in 3 gate times & 10s averaging to +/-1Hz
Freq Reference    Accuracy < 1/10^7/month, internal Xtal Oven & warming LED
Signal Generator  PLL 100Hz steps from 10 - 539.9999MHz, O/P -13dBm (50mV) BNC
Sig Gen Harmonics Better than -20dBc, Typically >-30dBc
Gen Attenuator    10x1dB & 8x10dB for 1.7uV-50mV, 40dB lower via Load Atten
Pilot tone(CTCSS) 4 Digit PLL 20-999.9Hz in 0.1Hz step, Mod Level, & Rx Counter
Modulation modes  CW AM FM & PM
AF Modulation     Internal/External, Level Pot & 20dB Atten.
AF Osc            Wayne type 100Hz-15.9kHz in 100Hz steps
Ext Mod/AF out    Needs >1V in, or 0-4V RMS AF out, 600 Ohm BNC
Xtal/IF           455kHz & 10.7MHz in built & ext Xtal socket & osc O/P BNC
AF Meter          Bal/floating 3mV-10V, 8 10dB ranges, 11Hz-27kHz -3dB
SINAD meter       Auto level, 1kHz Notch, 0 to -20dB/100-0% Noise & Distortion
Automatic Rx      Scans 2MHz->1GHz, 100mW-300W Load input, up to 60dB S/N
RF & IF O/Ps      Rear BNCs for RF & 450-470kHz IF
Rx AF Filters     Comms -3dB 300Hz-3kHz, or HiFi -3dB 50Hz-15kHz
Modulation meter  Auto Rx. +/- peak, AM 50/100%, FM 5/100kHz, PM 2/5 Rad
Monitor Amp & LS  Vol & 1W for Listening to: AF in, SINAD, AF Osc, & Rx
Power             AC IEC Mains input 230V/115 @ 60W, or XLR for 12V DC @ 5A
Weight            24kg in flight case

FULL CALIBRATION (see layout & access in previous bul) 
The PSU has only a -20V preset, & test points for all the other voltages. +26V,
15V, 8.5V, 5V, -12V.

For AM FM PM calibration of the Rx module (Tx Osc ref too) and for the AF volts
meter, I use a "FeelTeck Dual DDS Oscillator FY6600-60M" "calibrated by design"
source. (This is despite it having an AM mod meaning "% number" issue, & P-P
values needed.) Underside of Rx box are presets for FM PM & AM calibrations.
The AF voltmeter PCB has a cal pot too.

Auto tune Rx box has internal presets inside the inner RF box (as shown in
earlier bul). Set STOP preset for reliable action, then tune IF coils for
narrow bandwidth (scope IF O/P with wide dev sweep) and with constant level
from AGC for AM, centre the AFC action with FM discriminator for FM & PM modes
which are just able to give identical +/- 100kHz deviation readings.

Rx Splitter atten preset (small hole to bias DC on diodes in Tx mode)
adjustment needs to be enough so, no Rx overload occurs on an AM signal @ 300W
carrier (3W SMA after load), & still leaves good Rx sensitivity @ 100mW (1mW
after load).

Once the Rx is calibrated, it is easy to check the sig gen is working correctly
against it & the counter is functioning correctly too. Inside the RF oscillator
box there are presets for the RF AGC, 6 AM bias pots 1 for each osc and they
are adjusted for best modulation shape over each osc range, checked with a
scope from Rx IF for the 4 lower PLL tuned circuit freq centring. FM deviation
modulation sensitivity varies depending on the varicap voltage needed for the
frequency, so +/- 100kHz deviation is not possible at all frequencies!

SINAD meter cal with its AGC, is done with the AF osc patched from the AF Osc/
Rx mod O/P, and for the 100% level set frequency to 2-3 kHz, then @ 1kHz the 2
null pots adjusted, for lowest 0% reading (listen Sinad O/P). The AGC range can
cause some slight distortion, so calibrate over the AF level range needed.

CTCSS Frequencies are accurately clocked from the 4 dig thumbwheel data, so
should be accurately seen on the counter with the CTCSS measure button. For
lowest distortion, set @ 300Hz and scope (distortion analyse) the Rx wave shape
and adjust the + & - clipper presets for best shape. Adjust the set square @
800Hz, LF correction (Previous bul Mod 8/) pot @ 50Hz and redo again for best
results. Distortion should be < 2% from 50 - 800Hz.

AF Osc, the 160 dial up frequencies were trimmed with added Wayne bridge caps
for the LF end, & gain setting caps around the op amp for the 15.9kHz. All are
now within 1% as measured on the counter. Distortion is < 0.3% (-50dB) @ 1kHz.

RF Frequencies are clocked from the 7 dig leaver thumbwheel data & PLL, so it
is very accurate if reference is OK. For calibrating the reference oven, I use
a scope and viewed a 1MHz locked from a 198kHz off air standard, with the sig
gen set to 10MHz & adjust for no drift when it is properly warmed up (10mins).
This calibrates the 9 digit counter too.

RF Level should be -13dBm measured with atten set to max level at the pre- Load
Atten BNC link. Adjustment is the ALC present inside the nested Osc box. Level
flatness (+/-0.5dB 10MHz-539.9MHz). Each Osc coil is tuned for good PLL lock
voltages on band edges. RF harmonics & sig gen's 90dB atten checked @ all
frequencies on spectrum analyser. And the 300W dummy 20dB atten load & Splitter
box 20dB with analyser tracking gen.

Power meter has 6 presets for the 6 power ranges. These have only been compared
with other meters occasionally & itself on range steps.

The Reference IF osc frequencies of 10.7MHz & 455kHz are adjusted with the
counter using the 2 Xtal trimmers.

Rx/Tx Xtal test
1/ For Transceivers with plug in Tx & Rx Xtals, the activity and freq of Xtals
can be tested, and nominal frequency confirmed by patching O/P to the counter.
N.B. this can read the wrong freq on over-tone Xtals!
AF TEST Mic/LS ccts
2/ AF Osc with up to 4V can be sent to Mic or Rx Vol it etc. (attenuate as
required) and its level can be measured on AF meter (3mV to 30V FSD). The AF
stage gain can be determined with the AF meter on the stage O/P. Also
distortion can be measured @ 1kHz on SINAD meter. e.g. when the FM Dev clipper
comes in etc. without a scope.

3/Tx & Rx AF filters response shape can be measured too as above with the AF
Osc 100Hz-15.9kHz and AF Meter.

4/ Tx connected to N socket of the 300W Load atten input you can measure...

Ŀ Ŀ  Ŀ  a) Tx power 0.1-300W with 6x 10dB power ranges.
PSUĴTx>Ĵ Test set
     b) Frequency 1Hz - 540MHz to 1Hz res (1 or 10s gate).
                         c) AM Mod 0-50%, 0-100%, FM Dev 0-5kHz, 0-100kHz,
                            PM 0-2Rad, 0-5Rad.

                         d) CTCSS frequency, & Dev @-20dB (e.g. max +/-250Hz?)

                         e) Hear the AM/FM/PM modulation on Test set's LS.

5/ Tx connected to N socket of the 300W Load atten input you can measure...

Ŀ Ŀ  Ŀ            a) With external spectrum analyser after
PSUĴTx>Ĵ Test set               the 20dB high power atten & 20dB splitter
                  (40dB less), but the power meter's diode
      Mic  BNCĿ    load increases some of the harmonics!
          LinkSpectrum Analyser
        @-40dB  b) Other Tx spuri can also be safely seen.
                or a Scope on HF

6/ Tx connected to N socket of the 300W Load atten input you can measure...

Ŀ Ŀ  Ŀ            a) With a scope connected to IF output
PSUĴTx>Ĵ Test set>ĿRx          and 2nd Beam or Trigger from Rx AM Mod
     AM          then AM modulation linearity, or
      Mic   IF Ŀ mod         any AM Hum can be seen.

7/ With Rx AF mod BNC patched to AF input banana sockets on test set.

Ŀ Ŀ  Ŀ  a) AM/FM/PM Tx Signal Noise to <70dB can be measured
PSUĴTx>Ĵ Test set     via the Comms or Hifi filters.
      Mic       >   b) Hear the AM/FM/PM Tx noise on Test set's LS.
                Rx   AF

8/ Mod AF Osc BNC out patched to Mic (or acoustically) with a suitable atten

Ŀ Ŀ  Ŀ  a) AM/FM/PM Tx Distortion can be measured on SINAD
PSUĴTx>Ĵ Test set     Meter & hear notched distortion on Test set's LS.
    Mic<  >   b) AM/FM/PM modulation freq response 100Hz-15.9kHz.
          AFMod  Rx  AF     Read on AF meter's dB scale. (e.g. -40dB @ 4kHz??)
          1kHz              SSB response only done to the power meter.

                         c) Single Sideband actual Tx freq (+1kHz) measured.

9/ Rx patched to load N, or BNC after stepped atten. for 40dB more (50mW max).

Ŀ Ŀ  Ŀ  a) AM/FM/PM Rx can tested for freq error & selectivity
PSUĴRx<Ĵ Test set     with sig gen set to correct or off +/- frequency.
            Mod on/off   b) Rx CTCSS recognition, dev & sensitivity checks,
                            with and without comms mod present.

                         c) Rx S meter calibration checks. (S9+20dB HAHA!)

                         d) Rx Image Rejection, put in +/- 2x IF frequency etc.
                            and check RF level needed compared to normal Rx.

10/ Rx patched to load N, & Rx LS to AF input banana sockets on test set.

Ŀ Ŀ  Ŀ  a) AM/FM/PM Rx Frequency response seen on dB scale.
PSUĴRx<Ĵ Test set
     b) AM/FM/PM Rx Distortion @ 1kHz on SINAD meter.
     LS>AF  1kH or
             .1-15.9kHz  c) AM/FM/PM sensitivity MEASURED in uV/dBm, sig gen
                            set and 1kHz modulation for 12dB SINAD & best
                            sensivity including SSB (AM) mode.

                         d) AM/FM/PM max S/Noise (hum etc).

Sinad meter is used for best Rx S/N sensitivity & FM discriminator adjustments.
For that, 5 turns of the LS lead on a ferrite ring, stops it being an added
aerial on weak test signals! RF & DC leads may need the same treatment!

All of the above 24 rig tests, also permit rig adjustments to improve things.

With SSB kit AM mode has to be used to the Rx only. But SSB Tx 2 tone tests can
be done using CTCSS & beating AF osc (e.g. 0.8 & 1kHz) from mon LS to the mic &
scoping the Tx RF envelope (200Hz) beat note on a separate dummy load.

So a useful lab or /P test set. A one stop shop for all rigs, when taken to my
local club's regular test & fixit evenings.

See my tech Buls on "RTT Comms Test Set", Analyser Takeda Riken TR4122B", "AF
Waveform Generator (RS)", "RTT Mod Meter (100)", "FeelTeck Dual DDS Osc FY6600
-60M", "Marconi Distortion Meter TF2337","Marconi 2019A Sig Gen"," Systron
Donner 1702 Sig Gen" "Marconi Counter Type 2432A", "198kHz Off Air Standard",
"Comparing Off Air Freq Standards", "Off Air Lock for Ref Osc", & "Scope RF

Why don't U send an interesting bul?

73 de John, G8MNY @ GB7CIP

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