Modification of Radio Receiver-Transmitter, RT-505/PRC-25
for use with AN/PCC-1

FSN 5820-191-8936 for Mod Kit

©Brooke Clarke, N6GCE: edited and typed

1.    This modification is required to enable the radio to pass broadband frequencies of the AN/PCC-1 without deterioration of the signal.  The signal frequencies to be transmitted and received are 0.3 to 20 kHz.

2. The RT-505/PRC-25 Radio Receiver-Transmitter to be modified for use with the PCC-1 must meet the operating standards in the summary of test data paragraph 67 of TM 11-5820-398-35.  The radio must be correctly aligned before the modification is performed.  If the radio is not correctly aligned, the modification is ineffective.

3. Modification of the RT-505/PRC-25 Receiver-Transmitter requires modification of the modules A25 and A20, replacement of filter FL-3, replacement of module Z1, and installation of two coaxial cables.  After the modification, the band-pass characteristics are measured to assure that the broadband operation of the radio is acceptable for use on AN/PCC-1 Terminal Set.

4. After assurance that the receiver-transmitter complies with the tests in accordance with TM 11-5820-398-35, Chapter 4, Section III, set up the receiver-transmitter in accordance with figure 1 to record the readings of the receiver output.  Remove the case from the radio chassis.  (See paragraph 13).

5. In addition to the test equipment required by TM 11-5820-398-35, the following is required:

Set the controls of the C-7673/PCC-1 Control Unit-Rectifier as follows: 6.    TS-382/F Audio Signal Generator: Set output meter to 1.0, multiplier to X10.  Connect output ot EXT MOD input connectors of the RF Signal Generator AN/URM-48.

7.     AN/URM-48 RF Signal Generator:  Set frequency output to 30 MHz and RF meter to line.  Set modulation to EXT MOD, adjust deviation to 10 kHz (on 25 kHz range).  Set RF attenuator to 0.7 micro volts.

8.    ME-30B/U AC Voltmeter:  Connect the ME-30B/U to pins A (common) and B (AUDIO) of the MX-9185/UR Adapter to perform the following tests.

9.    Test the DC voltage supply of the C-7673/PCC-1 Control Unit-Rectifier.  Measure positive 13.5 VDC at terminals E and F and positive 3 VDC at terminal H of the Test Adapter MX-9185/UR.  Terminal J is ground.

10.    Response Measurements:  Adjust the receiver-transmitter volume control to it's maximum clockwise position.  Set the TS-382 Audio Oscillator to each frequency setting of table 1 and record the receiver response obtained at terminals A and B of MX-9185/UR in table 1.  Plot the readings of table 1 in graph, figure 8, as "before modification" for use later to see the change.

Table 1.  RT-505B/PRC-25 Receiver Response Measurements

 
Audio Oscillator
TS-382F/U
Frequency
Setting
kHz
Unmodified
Radio
receiver
response
dB
Modified
radio
receiver
response
dB
Requirement
for modified
radio
1.0
0
 
0
0.3
-1
 
-10 +/- 2 dB
0.5
0
 
-10 +/- 2 dB
7.0
-12
 
-10 +/- 2 dB
11.0
-18
 
-10 +/- 2 dB
15.0
-24
 
-10 +/- 2 dB
20.0
-29
 
-6 +/- 2 dB
       
11.    At the completion of the receiver-transmtter test, set the function switch of the receiver-transmtter to OFF.  Set the C-7673/PCC-1 Power Source switch to OFF and disconnect the receiver-transmitter from the test setup.

12.    Perform the modification of the RT-505/PRC-25 Radio Receiver-Transmitter in the following steps.

13.    Loosen and disengage the four captive screws that secure the RT-505/PRC-25 case.  Pull the RT-505/PRC-25 straight out of its case.

14.    Modification of module A25 (figure 2) removes the noise bypass capacitor C7 form the module.

(a)    Remove the two module pulling tools from the module pulling tool holders.  Be careful not to cross thread the module bulling tools in the module tool receptacles.

(b) Screw the module pulling tools into the module tool receptacles on the A25 module.

(c) Loosen and disengage the module retaining screw.

(d) Remove the module by pulling the module pulling tools.

(e) Remove the module pulling tools from the module;  replace them in the module pulling tool holders.

(f) Loosen and disengage the module cover retaining screws.

(g) Remove the module cover.

(h) Unsolder and remove C7 (figure 3).

(i) Clean the exterior surfaces of the module cover, which should be free from dust, dirt and grease.

(j) Position F60478 label on top of module cover.  Remove protective cover from the back of the label and press firmly in location selected.

(k) Place the module cover on the module base.  Engage and tighten the module cover retaining screws.

(l) Make sure that the module jacks mate with the module plugs when the module is being reinstalled.  Place the module into position on the chassis (figure 2).  Seat the module in it's connectors by applying pressure to each end of the module.  Tighten the module fastening screw.
 

15.     Remove 11.5 MHz filter and replace with filter, bandpass, F-1209/PCC-1 (figure 2).  Filter F-1209/PCC-1, affords wider frequency response for multiplex wide band operation.
(a) Tag and unsolder the wiring to the terminals of FL3.

(b) Loosen and disengage the three captive screws that retain the audio and control chassis A27.

(c) Swing A27 open on its hinge to gain access to the fastening screws of FL3.

(d) Remove the nuts and washers from the fastening screws and remove FL3.

(e) Swing A27 closed on its hinge and position Filter, bandpass F-1209/PCC-1 as shown in figure 2.

(f) Swing A27 open on its hinge to access the fastening screws of filter.

(g) Replace the washers and tighten the nuts to the fastening screws of F-1209/PCC-1.

(h) Swing A27 closed on its hinge.

(i) Solder all electrical leads to the terminals as shown in figure 4.

16.    Remove discriminator module 21 and replace with filter, band-pass F-1219/PCC-1 (figure 2).  This improves linearity and broadband frequency response of the IF filter.
(a) Unsolder the wiring to the terminals of Z1.

(b) Swing A27 open to gain access to the fastening screws of Z1.

(c) Remove the nuts and washers from the fastening screws and remove Z1.

(d) Install and solder cable A, end x (figure 2 and paragraph 17), in position.

(e) Swing A27 closed on its hinges and position Filter, band-pass F-1219/PCC-1, as shown in figure 2.

(f) Swing A27 open on its hinge to gain access to the fastening screws of filter.

(g) Replace the washers and tighten the nuts on the fastening screws.

(h) Swing A27 closed on its hinge.

(i) Solder all electrical leads, as shown in figure 2.

17.    Install cable A (F60334).
(a) Cable A has, at one end, a shield and conductor; this end is referred to as x; the other end, as y.

(b) Solder cable A, end x, to terminal posts adjacent to module Z1, as shown by schematic diagram (figure 4).  Use F54153 sleeve where indicated.

(c) Position cable on audio and control chassis A27, figure 2.

(d) Loosen cable clamp retaining screw; do not remove.

(e) Pass cable through cable clamp loop.

(f) Swing A27 open on its hinge and tighten cable clamp screw.

(g) Swing A27 closed on its hinges.

(h) Pass cable through bushing in wall of A27.

(i) Swing A27 open on its hinges; position the radio set with its front panel on a flat surface.

(j) Solder cable A, end y, to J3 terminal P, as shown by schematic diagram (figure 4).  Use F54154 sleeve where indicated.

(k) swing A27 closed on its hinge.

18.    Install Cable B
(a) Cable B has, at one end, a shield and conductor; this end is referred to as x, the other as y.

(b) Swing A27 open on its hinge.

(c) Solder cable B, end x, to synthesizer mother board A26, center conductor to pin E and shield to pin D of J-16, as shown by schematic diagram (figure 4).  Use F54153 sleeve where indicated.

(d) Feed cable under A26 (figure 6).  Dress cable with existing wiring harness.  It may be necessary to loosen A-26 circuit board to assist in feeding the cable under the board.

(e) Loosen cable clamp retaining screws; do not remove.

(f) Pass cable through clamp; tighten clamp screws.

(g) Position radio set on its front panel on a flat surface.

(h) Dress cable behind existing wiring harness at rear of front panel to J3 (figure 2, View A-A).

(i) Solder cable B, end y, to J3 terminal R, as shown by schematic diagram (figure 4).  Use F54153 sleeve where indicated.

(j) Swing A27 colsed on its hinge.

19.    Modify sidestep oscillator, Module A20 (figure 5).  This applies broadband signals to the junction of R8, R7 and C5, via pin E of J16, directly into the sidestep oscillator, bypassing module A22.
(a) Loosen the three captive screws that hold audio and control chassis A27 in position (figure 2).

(b) Swing A27 open on its hinges to reach the module fastening screw (figure 6).

(c) Loosen the module fastening screw.

(d) Pull the module out with your fingers.  (Slight pressure on loosened fastening screw may aid this removal).

(e) Remove the module cover retaining screw and washer.

(f) Remove the module cover.

(g) Solder Wire F60324 in position indicated by figure 7.

(h) Clean the exterior of the module cover.

(i) Position an F60478 label on module cover on opposite side of identification markings.

(j) Remove protective cover from the back of the label and press firmly in position.

(k) Position cover on module base.  Make sure that the hole in the cover marked J2 aligns with connector J2.

(l) Replace the module cover washer and retaining screw.  Tighten the screw.

(m) Make sure that the module jacks mate with module plugs when the module is being reinstalled.  Place the module into position in the RT-505/PRC-25 (figure 5).

(n) Seat the module in its connector by applying pressure to the center of the module.

(0) Swing audio and control chassis A27 open on its hinge to gain access to the module fastening screw.

(p) Tighten the module fastening screw (figure 6).

(q) Swing audio and control chassis A27 back into position.

(r) Tighten the three captive screws that were loosened in accordance with preceding paragraph 19(a).

20.    Refer to figure 1 and paragraph 2 for test setup.
(a) Repeat the audio response test of paragraph 6-2d at 300 Hz, 500 Hz, 1 kHz, 7 kHz, 11 kHz, 15 kHz and 20 kHz, and record the readings in table 1.  Plot the response readings recorded in table 1 as "after" in graph figure 8.  The "after" will show a marked rise at the high frequencies.

(b) Remove the cover from the A21 module of the RT-505/PRC-25 under test and loosen the Glyptol on L4, T1 and T2 with a drop of solvent (methyl-ethyl-ketone, aka MEK).

(c) Set the Audio Signal Generator, TS-382, to 19 kHz and adjust L4, T1 and T2 for a maximum dB reading on the ME-30B Meter.  Adjust the tunable slug in the A5 module for  a minimum reading on the ME-30B mater.

(d) Recheck the frequency response curve to ensure against excessive loss at 300 Hz and large dips at the middle frequencies.  The response at 300 Hz should be approximately 10 dB down +/_ 2 dB and at 18 kHz, approximately 6 dB +/- 2 dB.
 

21.    (a) Wipe the inside of the case with a clean, lint free cloth; make sure that its interior is dry.  Inspect the gasket adjoining edge on the front of the case for chips or burrs.
(b) Carefully move the case over the chassis; make sure that the plug aligns with the hole in the rear.  Be sure the front panel is seating evenly on the gasket.  Tighten the case securing screws.
22.    Use a label F60478 to indicate that the receiver-transmitter has been modified for use with AN/PCC-1.
(a) Clean the front panel area to receive the label.

(b) Position label on front panel above PRESET.

(c) Remove protective cover from the back of the label and press firmly to secure.

(d) The RT-505/PRC-25 modified in accordance with the foregoing procedures is renomenclatured RT-505B/PRC-25.

Packing List for FSN 5820-191-8936 for Mod Kit

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