AN/FRT-24 Navy 1kw HF AM/CW Transmitter

1951 Advertisement for Collins Type 430 transmitter family - thanks to 

Video showing autotune operation of K6GLH's AN/FRT-24

Video showing operation of KC8ZUL's AN/FRT-24

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AN/FRT-24 photos - thanks to Phil KS4FE

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AN/FRT-24 Transmitter Photos - thanks to Russ WA3FRP

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C-1362/FRT-24 Remote Controller
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010_016.jpg (179169 bytes) 011_015.jpg (150326 bytes) 4-1000A driven by 4-65A
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4-1000A driven by 4-65A
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014_012.jpg (189114 bytes) 016_010.jpg (140862 bytes) Pair of 4-400's in modulator
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019_007.jpg (171380 bytes) 021_005.jpg (191399 bytes) Power Supply for Master Oscillator
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Master Oscillator
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CU-390/FRT-24 Output coupler found at Dayton hamfest

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TRANSMISSION LINE COUPLER CU-390/FRT-24 (see figure 2-29) .-The Transmission Line Coupler is a device that provides both balancing and impedance transformation. It matches the unbalanced 52-ohm output from the pi-L coupler of the transmitter to a balanced 600-ohm, two-wire line feeding the antenna system Figure 2-30, A through C, illustrates the basic theory from which this coupler was derived. Figure 2-30A shows an ideal long transmission line whose input impedance (Zin) is equal to the terminating or output impedance (Zo) and also shows an ideal matching transformer with a balanced input and a balanced output and an impedance-matching ratio of 1:1. If long, equally terminated transmission lines are connected in parallel at one end and in series at the other end, the output impedance (Zo), as shown in figure 2-30B, the result is the same as putting lumped resistances in series at the Zo end and in parallel at the Zin end. The impedance transformation at the input end (looking from the coupler to the transmitter) is step down, and at the output (looking from the coupler to .the actual antenna transmission line), step up; in either case, it varies as the square of the number of transmission lines used regardless of whether the circuit constants are lumped or distributed. Since three separate transmission lines are used, the output impedance (Zo) will appear as nine times Zin, or 450 ohms, for balanced impedance transformation.
Figure 2-30C shows the equivalent circuit for the conditions represented in figure 2-30B except that an unbalanced input is fed through the coupler to a balanced output; the circuit also uses artificial transmission lines having lumped constants instead of long terminated lines. If a 600-ohm load is connected across the 450-ohm·output of this device, a standing-wave ratio (SWR) of 1.33:1 (600/450) will exist, assuming a balanced input and output condition. In practice, this is very difficult to achieve with antennas and transmission lines, particularly when they have to work over a wide frequency range such as 2 to 30 mc. Any unbalanced currents in the transmission line would cause a high standing-wave ratio, with subsequent distortion of the radiation pattern. Lumped transmission lines L2001 and L2002, L2003 and L2004, and L2005 and L2006 are arranged so that their windings offer opposition 'to the flow of unbalanced currents (always in the same direction) and no opposition to the flow of balanced currents (always in opposite directions) . Balance is obtained by the use of a coil Balun, L2011, to couple the matching unit to the unbalanced 52-ohm transmitter output jack (P2001). frt24-cplr-man-03.jpg (1975882 bytes)
This Balun consists of a coaxial line wound as an inductance and connected as shown in the schematic in figure 2-29. As connected, the center conductor of the grounded half of this coil is not used, and the circuit operates as if it were comprised of two tank circuits balanced to ground. The unbalanced 52-ohm output, taken from Radio Transmitter T-440/FRT-24 through an RG-17/U coaxial cable and connector J107, is introduced to a 52-ohm balanced circuit, L2011, which converts this output to a balanced 52-ohm input. This input impedance is then stepped up in impedance by a device similar to the type discussed above. L2011 is made up of two sections of coiled r-f coaxial cable, which together with their distributed capacitances, act as two parallel resonant circuits equivalent to a center-tapped input over the entire operating range to maintain line balance. L2011 covers a 4 :1 range in frequency; the use of capacitors C2001 through C2064 ( 64 capacitors in all) and coils L2009 and L2010 extends the low-frequency range and the over-all coverage to 15:1. An improvement in the standing-wave ratio is obtained by the use of tuned circuit C2065 and L2007, in series with the sections of artificial transmission line consisting of spiral windings L2002 and L2003; and by the use of tuned circuit C2006 and L2008, in series with the other sections of artificial transmission line consisting of spiral windings L2004 and L2005. Two loading coils (L2012 and L2013) are used to extend the frequency range of the coupler to 31.25 mc at the high-frequency end of the range, to prevent an otherwise rapidly rising SWR at 30 mc. These series loading coils, together with the feed-through bowl capacitance of 3.6 micromicrofarads to ground (existing at E2003 and E2004, and E2005 and E2006, respectively), also form a small L-type network that matches the 450-ohm theoretical output impedance of the coupler to a 600-ohm load. A horn gap, E2013 and E2014, connected to one side of the balanced line, and E2015 and E2016 connected to the other, protect the equipment from .damage due to extremely high voltage surges such as occur during lightning storms.

O-243/FRT-24 oscillator seen on eBay

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Related Collins 432D-2 Commercial Transmitter
thanks to Russ WA3FRP

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