Sensitivity Alignment

548 Pages·2016·10.05 MB·English

R-390A notes on alignment and overall sensitivity
---------------------------------------------------------------------------------------
Measuring Receiver Sensitivity by Chuck Rippel
------------------------------------------------------------------------------------------------------------
----
There may be an occasion when its appropriate to measure and record
receiver sensitivity in real terms using an accepted standard.     For radio
receivers, real term sensitivity is expressed as the value of a modulated RF
voltage applied to the antenna input necessary to provide a 10db S/N + N
figure.   This means, what input voltage is required to raise audio output
10 db over the receiver noise floor.
Measuring the receiver sensitivity in the R390A is an easy, straight
forward procedure.  The receiver Line Level meter can even be used to help
with the measurement.   Here is the procedure:
1- Turn the receiver and signal generator on and allow them to warm up
for 1 hour.
2- Put the receiver and generator on 4.8 mHz (or any other frequency of
choice)
3- Set the initial generator output to 1µv and modulation level 1kc, 30%
but do not connect the antenna input yet..
4- Set the R390A Function switch to "MGC," Bandwidth to 4kc, RF gain full
CW, BFO off.
5- Set the Line Meter range switch to -10 and carefully adjust the Line
Gain control for a -10db indication on the Line Level meter.
6- Watch the Line Level meter and peak the Ant Trim on receiver noise
alone; readjust the Line Gain control for a -10db indication on the Line
Level meter.  This level is now indicating a relative level of the receiver
noisefloor.
7- Connect the generator to the receiver antenna input (I use the
"Balanced" input) and adjust the Kilocycle Change control to center the
output of the generator in the receiver passband.
8- Adjust the RF output level of the generator to cause the Line Level meter
on the R390A to read "0."
9- Note the output of the generator in microvolts.  This value is the 10db
S/N + N receiver sensitivity.  It should be less than 0.5uv although the
official specifications of the receiver call for 3 microvolts.
...........................................................................................................................................
Once the receiver sensitivity has been established, you can then "massage"
the IF Gain (usually by dropping in nearly all the way) and tube lineup for
the best recovered audio.  The technique to "massage" the If gain is covered
in the Technical, IF Gain section of this site. Optimizing the vacuum tube
lineup in the signal part is another technique to maximize performance. 
Because changing them does not require re-alignment, an easy start is to
work with the tubes in the signal path of the IF strip.  These are the
5749W's IF amps, V-501, V-502 and V-503. The 6AK6 4th IF amp V-504
and the detector, V-506, a 5814A. With your generator set up and the
receiver at step 8 above, install a replacement tube at V-501, allow it to
warm up about 5 minutes and note the indication of the Line Level Meter.  
If it climbs above 0db, the new tube has improved gain, if not, reinstall the
old tube.   Repeat the same steps for V502, V503, V-504 and V-506.  You
may "find" a few extra db in your spare tube stores.
-----------------------------------------------------------------------------------------------------------
-
© 1996, 1997, 1998 Charles Rippel - All rights reserved.
------------------------------------------------------------------------------------------------------------
-
R390A IF Deck Alignment (Chuck Rippel)
R390's made after 1954 and those with mod 2 stamped on the IF chassis
have a field change installed to the mechanical filters. Filter input and
output trimmer capacitors have been added. The 4 input trimmer
capacitors are found by removing the 2 square can on top of the IF chassis
using the single nut in the top. The 4 output trimmer capacitors are
located behind 4 holes in the left hand side of the IF deck. The IF chassis
will need to be loose but still electrically connected to complete these
procedures.
An accurate counter, analog VTVM and a signal generator capable of
outputting 455.00 KC, is required for these alignments.
Connect the VTVM to the Diode Load bus on the rear and configure it to
read a negative voltage of approximately -7vdc. Set the receiver
FUNCTION control to MGC, BFO to OFF and the LOCAL GAIN control to a
comfortable level. Lift and tilt the IF deck resting the front captive (green)
screw over the front panel. You should be able to gain access to the
mechanical filter trimmer capacitors through the large ventilation holes
in the main chassis.
Locate the cable running from the rear of the IF deck to the *IF OUT* BNC
connector in the rear panel, upper left side. Unplug the cable from the IF
deck only. Also unplug J-513 and the one next to it. Plug the cable
running from the rear IF Out jack into J-513 on the IF deck. Connect the
output of your 455.000 kc generator.
------------------------------------------------------------------------------------------------------------
----
Mechanical Filter Alignment-
Set the 455kc generator output level to cause the VTVM to read about -
2.5V.
With the IF deck oriented so that the bandwidth control is towards you,
set the bandwidth to 2Kc and align 1 of the four top trimmers.
Adjust C-569 which is at 9 o'clock for a peak on the VTVM.
Next, align the output trimmer in the left side of the IF deck, labeled C-567
Set the BW to 4KC
Align the top trimmer, C-568 located at 12 o'clock
Align the side trimmer, C-566 located at rear, bottom.
Set the BW to 8kc
Align the top trimmer, C-570 located at 6 o'clock.
Align the side trimmer, C-565 located at front, top.
Set the BW to 16kc
Align the top trimmer, C-571 located at 3 o'clock
Align the side trimmer, C-564 located at front, bottom.
------------------------------------------------------------------------------------------------------------
-----
IF Transformer Alignment-
Select the 16KC filter
Set the generator frequency to 467kc. Note: The generator output should
be increased until the VTVM indicates approximately -2vdc. Do not be
alarmed if that level is over 0.1 volts. Adjust the top slug (secondary) of T-
501 for a peak reading on the VTVM, Adjust the bottom slug (primary) of
T-502 for a peak reading on the VTVM
Set the generator frequency to 443kc. Note: The generator output should
be increased until the VTVM indicates approximately -2vdc. Again, do
not be surprised if that level is over 0.1 volts. Adjust the bottom slug
(primary) of T-501 for a peak reading on the VTVM, Adjust the top slug
(secondary) of T-502 for a peak reading on the VTVM. Decrease the
generator output and adjust the frequency to 455kc Note: The generator
output should be decreased until the VTVM indicates approximately -
3vdc.Select the 4kc filter then peak top and bottom of T-503 only
------------------------------------------------------------------------------------------------------------
----
AGC Alignment-
Verify the generator is still outputting 455.00kc. Set the FUNCTION
switch to AGC and connect the VTVM between the AGC bus on TB-102 3 &
4 located on the rear panel & ground.
Adjust the generator output for a reading of approximately -5vdc on the
VTVM. Peak Z-503.
------------------------------------------------------------------------------------------------------------
----
BFO Alignment-
Verify that generator is still at 455.00kc
Turn on the BFO and exactly zero beat it against the 455.00 generator
frequency.
Loosen the bristo spline socket on the BFO shaft coupler,
Verify that you still have exact zero beat.
Set the BFO Pitch control to indicate exactly 0.
Then, tighten the bristol socket on the non-mar clamp on the BFO shaft
coupler
The filters have been aligned to 455 kc.
(When a station broadcasting in AM is zero beat, the carrier will be in the
center of the filter selected).
Re-install the IF chassis in the receiver.
---------------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------------
Setting the IF Gain Control for best performance
The most common single item responsible for holding an R390A back is
not lack of sensitivity. Rather it is internally generated IF deck noise. In
an otherwise properly operating R390A, the cause of this excessive noise
is IF gain control being set to high. Even the mfg spec of setting the IF
deck gain such that -7vdc at the diode load when fed by 150uv @455kc
into J-513 is far too hot.
Here is a recently refined procedure to set the IF deck gain control.
Anyone can perform the procedure whether they have access to a signal
generator or not.
------------------------------------------------------------------------------------------------------------
Procedure to set R390A IF Gain-
Once the receiver has been fully mechanically and electrically aligned, the
final procedure to perform before buttoning it up is to set the IF gain
control. Many otherwise very sensitive R390A's are thought not to be due
to weak signals being covered by noise generated by excess IF deck gain.
Allow the receiver to warm up for at least 1 hour then:
Disconnect the antenna
Set receiver for 15.2 mHz
Set the FUNCTION control to MGC
Select the 4kc filter with the BANDWIDTH
Set RF GAIN control to 10 or maximum
Peak the ANTENNA TRIM for maximum noise as indicated on the LINE
LEVEL meter
Set Line Meter switch to -10db scale
Set Line Gain control to full CW or 10.
Adjust IF gain control, R-519 to cause Line Level meter to indicate
between -4 to -7 db.
Re-zero the carrier meter control, R-523
Set controls above for normal operation and reconnect antenna
Discussion:
This will yield the best compromise on all bands. I usually poll those
bands which I normally spec out. Then, using an HP signal generator set
for internal modulation of 800 hz @ 30%, massage the gain setting and
even specific signal path tube selections for the best overall performance.
Contribution by Chuck Rippel, WA4HHG
------------------------------------------------------------------------------------------------------------
-
from EIB-836:
-----------------------------------------------------------------------------------------------------------
Variable IF Reference & Stage Gain
by Chuck Rippel
12/24/2001
Part of the secret behind the R390A's incredible selectivity and its
immunity to near RF fields is found in the two tracking IF sections. The
First Variable IF operates while receiving frequencies below 8 Mhz and is
tuned to pass IF signals from 17 to 25 mhz. This represents the sum of
the actual received frequency that is amplified by V-201 and then applied
to the grid of the First Mixer, V-202. The 17.0 Mhz output from the 1st
Crystal Oscillator, V-207 is also applied to the cathode of the same tube.
The signal represented by that sum is directed to the tracking coils Z-213-
1, 213-2 and 213-3 which are kept tuned to the correct frequency within
the 17 - 25 mhz IF frequency range by the cam system. This signal is then
known as the First Variable IF Frequency.
During reception of frequencies 8 Mhz and below, the composite output of
the First Variable IF is routed through S-208 (front), then C-286 and is
applied to the grid of the 2nd Mixer, V-203. For reception of frequencies 8
Mhz and above, the amplified recived signal signal from V-201 is routed
around the First Mixer by S-206 and applied to the grid of the 2nd Mixer
through S-208 and C-286. The output of the 2nd Crystal Oscillator, V-401
is also applied to the cathode of V-203. The resultant output is the 2nd
Variable IF Frequency which is always between 2 and 3 Mhz. That
difference is applied to the tracking coils Z-216-1, 216-2 and 216-3 which
are also kept tuned to the correct frequency within the 2-3 Mhz IF
frequency range by the cam system.
The 2nd Variable IF frequency is applied to the grid of the 3rd mixer, V-
204 where it is mixed with the output of the PTO (V-701) applied to pin 7.
The PTO tunes from 3.455 to 2.455 Mhz . The difference frequency
between the 2nd Variable IF Frequency and the output of the PTO is
always 455kc. This difference frequency is applied to T-208 which is
tuned to 455kc. The result is the 3rd IF Frequency which is then routed
from the RF deck to the IF sub-chassis through P-213 and P-218.
In analyzing a failure in the variable IF system, it can be seen that a signal
related failure in the First Variable IF will result in low gain during
reception of only the frequencies below 8 Mhz. A like failure in the 2nd
Variable IF or 3rd IF would affect all frequencies.
Here is a quick test to see if the Variable IF stages are generally working.
Initial checks:
First Crystal Oscillator output as measured at pin 7 of V202:
Normal is approx 4V P-P
SecondCrystal Oscillator output as measured at pin 7 of V-203:
Normal is approx 3.2V P-P
PTO output measured at pin 7 of V-204:
Normal is approx 6V p-p
First Variable IF Gain Test:
Tune the receiver to 00 500, AGC OFF, VTVM connected to read voltage at
the rear Diode Load point.
Inject a 17.5 Mhz signal at approximately 15uv through an RF coupled
probe to E-210. This should result in a reading of approximately -5V at
measured at the diode load point. This bypasses the coils Z-216-1, 216-2
& 216-3 and can be used as a reference.
Inject a 17.5 Mhz signal at approximately 40uv through an RF coupled
probe to pin 1 of V 202. This should yield approx -3.5V at the diode load
point.
Discussion: An indication at the diode load point of approximately 1.5V of
loss is nominal. If there is loss which cannot be corrected by proper
alignment of coils Z-216-1, 216-2 and 216-3 or no signal at all, change
the injection point coil to coil to moving "away" from the 2nd mixer to find
the failure.
Second Variable IF Gain Test
Tune the receiver to 01 000+, AGC OFF, VTVM connected to read voltage
at the rear Diode Load point.
Inject a 2.0 Mhz signal at approximately 15uv through an RF coupled
probe to pin 1 of V203. This should result in a reading of approximately -
2.2V at measured at the diode load point. Again, this bypasses the coils
Z213-1, 213-2 & 213-3 and can be used as a reference. Inject the 2.0 Mhz
signal at approximately 15uv through an RF coupled probe to pin 6 of V-
204. This should yield approx -4.2V at the diode load point.
Discussion: An indication at the diode load point of an increase of
approximately 2V is nominal. Again, If there is loss which cannot be
corrected by proper alignment of coils Z-213-1, 213-2 and 213-3 or no
signal at all, change the injection point coil to coil to moving "away" from
the 2nd mixer to find the failure. To align the variable IF stages, I use a
different method from that found in the various military manuals. My
technique yields better results by taking a systems approach and also not
loading down the stage to be aligned. Its a bit lengthy to explain here but
that procedure, along with many other techniques are demonstrated in
the 7 hour long, R390A video tape series available from Hi-Res
Communications. Don't forget to ask about the new 4 hour addendum to
the 7 hour series.. R. Charles Rippel
--------------------------------------------------------------------------------------------------------
Date: Sun, 12 Oct 1997 10:03:40 +0500
From: "Chuck Rippel" <crippel@...>
Subject: [R-390] R390A alignment note
The following is probably the single most important alignment
component in the R390A receiver. It's relevence is not really spelled out in
any of the techincal manuals I have seen but it is the real key to getting
the receiver properly aligned.
- - - -
PTO tracking on the R390A is very important. Due to the tracking nature
of the RF and IF circuitry, the PTO end points must be very carefully
adjusted. If the PTO is "long" or "short," it will not tune in the designed 1
mHz segments that match the mechanical cam profiles which drive the
slugs in the various coils. In as much as I restore R390A's, I find that PTO
mis-tracking by a little as 10 kHz can noticably degrade overall
performance. Don't believe it? Losten the PTO coupler then tune the radio
on simple band noise. At this point, changing frequency with the
KILOCYCLE CHANGE knob will only tracking the cam stacks and not the
PTO. Observe that the band noise drops away at about (+-) 7 kc or so from
your original frequency. That's is how tight the mechnical tracking on the
'390A is.
Here is a quick check for proper PTO tracking: Let the radio warm up for
about an hour.
Tune the radio down to (-) 000 and zero beat the calibrator. Next, tune the
radio up and note the frequency where it zero beats. The dial should read
close, say to plus or minus 3 kc's of (+) 000. If that is not the result, both
the PTO end points AND the dial over run need to be reset. This is followed
by setting (timing, actually) the various cams which now need to be
mechanically realigned. Follow this by an an electrical alignment as
outlined on top of the "Utah shaped"
plate on top of the RF deck.
Successful completion will result in the mechanics of the receiver tracking
with the electronics.
-------------------------------------------------------------------------------------------
Date: Sat, 1 Nov 1997 23:56:59 +0500
From: "Chuck Rippel" <crippel@...>
Subject: [R-390] Filter and BFO alignment
R390A's made after 1954 and those with "mod 2" stamped on the IF
chassis have a field change installed to the mechanical filters. Filter input
and output trimmer capacitors have been added. The 4 input trimmer
capacitors are found by removing the 2" square can on top of the IF
chassis using the single nut in the top. The 4 output trimmer capacitors
can be seen behind 4 holes in the left hand side of the IF deck.
If you have a counter and a generator which can put out 455.00 KC, you
can align filter network:
Connect a VTVM (NOT DVM) to the "Diode Load" bus on the rear and
configure it to read negative voltage. (It'll be about -5 volts)
Locate the cable running from the rear of the IF deck to the "IF OUT" BNC
connector in the rear panel, upper left side. Unplug the cable from the IF
deck only. Also unplug J-513 and the one next to it. Plug the cable
running from the rear "IF Out" jack into J-513 on the IF deck. Connect the
output of your 455.00kc generator.
Set the .455kc from the generator to cause the VTVM to read about- - 2.5V
With the If deck oriented so that the bandwidth control is towards you, set
the bandwidth to 2Kc and align 1 of the 4 the top trimmers. Adjust the one
which is at 9 o'clock for a peak on the VTVM. Next, align the output
trimmer in the left side of the IF deck, located at rear, top.
Set the BW to 4KC
Align the top trimmer located at 12 o'clock.
Align the side trimmer located at rear, bottom.
Set the BW to 8kc
Align the top trimmer located at 6 o'clock.
Align the side trimmer located at front, top.
Set the BW to 16kc
Align the top trimmer located at 3 o'clock
Align the side trimmer located at front, bottom.
Peak top and bottom of T-503 only!
Verify that generator is still at 455.00kc
Turn on the BFO and exactly zero beat it against the 455.00 generator
frequency. Loosen the bristol spline socket on the BFO shaft coupler, verify
that you still have exact zero beat. Set the "BFO Pitch" control to exactly
"0" then tighten the bristol socket on the non-mar clamp on the BFO shaft
coupler
The filters have been aligned to 455 kc. When you zero beat a station
broadcasting in AM, the carrier will be in the center of the filter selected.
------------------------------------------------------------------------------------------------------------
Date: Wed, 5 Nov 1997 11:08:49 +0000
From: crippel@...
Subject: [R-390] Re: R390A question
> Thank you Chuck for coming back to my call.... I have a 1st OSC problem
> in the R390A. After it gets good and hot in the chassis the osc dies.
> Sometime I can shock it back by unplugging the heated xtal assy. I
> thought I fixed this about 4 yrs ago when I first got the rcvr. Any way
> do you have any suggestions ? I am going to pull it out of the rack and
> start snooping. I have a manual and the radio never saw military service
> so the radio is really in very nice shape. TNX again FRED KC4MOP
See that one all the time as it kills wht low bands when it fails.
The fix is; its an easy. Remove the HR-202 xtal assy and:
A: Replace it (Fair Radio has replacements)
B: Take it a part and put a new 17mhz crystal in it. May as well replace the
calibrator crystal while you're at it. It fails also. I favor "B" as the HR-202
assy's are getting hard to find. '390A xtals, 1st and 2nd oscillators) are
dying right and left due to age. International crystal has the JAN cross
reference. Take the number off the crystal case, (I know that the the
R390A 2nd oscillator crystals are HC6/U) and give it to them.
----------------------------------------------------------------------------------------------------------
From: rerobins@... (Rick Robinson)
Date: Tue Nov 18, 1997 1:18 pm
Subject: [R-390] RF alignment
My radio weekend was nearly ruined by sunny skies and temps in the
high'50s. Fortunately the "honey do" list was very short so there was
plenty of R-390A time.
Now that the front panel is off, here is the next bear to cross. My RF cams
do not align anywhere in the 7Mcs band. Part may be my fault in my