brief specs on various rigs available...
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GRC-46
The T-195 & MD-203 combo makes true FSK and is hardwired for MARK HIGH ops. The CV-278 is switchable MARK HIGH or MARK LOW. The GRC-46 junction box can be modified to allow transmitting MARK LOW.
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GRC-106
The GRC-106 is a USB radio, and the MD-522 is normally set up for MARK LOW ops. Easy to set it up for MARK HIGH - for receive the switch is on the front panel and for transmit the switch is on an internal module.
The GRC-106 receiver/exciter has a 'FREQUENCY VERNIER' control, but it changes the receive frequency only.
Early GRC-106s tune in 1KC increments, but the GRC-106A tunes in 100CPS increments.
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PRC-47 & CV-2455
The PRC-47 is a USB only radio, and the CV-2455 was originally hardwired for MARK HIGH ops - this combination is probably the least agile of all military RTTY sets. The radio tunes in 1KC increments.
There is a Marine Corps Modification Instruction for the CV-2455 - it changes the unit around for MARK LOW ops.
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TRC-75
The TRC-75 is normally set up for MARK HIGH ops, but can switch to MARK LOW by changing sidebands. It tunes in 1KC increments, so the swap sidebands trick works only if the RF center frequency is on a 1KC interval.
The CV-786 (the modem in the TRC-75) can be changed to MARK LOW, and there is a Marine Corps Modification Instruction to do just that.
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TSC-15
The TSC-15 is normally set up for MARK HIGH ops, but can switch to MARK LOW by changing sidebands. It tunes in 1KC increments, so the swap sidebands trick works only if the RF center frequency is on a 1KC interval.
The CV-1086/TGA-1 (the 850 shift modem used in the TSC-15) can be changed to MARK LOW, and there is a Marine Corps Modification Instruction to do just that.
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Al Tipsword W6GER, myself, and a group of other 850 shift enthusiasts meet weekly on 30 meters. We use MARK LOW USB ops, in order to accomodate standard PRC-47 & CV-2455 sets & standard GRC-106 sets. Al is running a Kleinschmidt page printer with either a PRC-47 & CV-2455 setup or a GRC-106, and I use either a battery-powered PRC-47 & CV-2455 & 28V MITE teleprinter or a Sunair RT-9000 & Dovetron & Model 28 skintight.

We'd be pleased if you would join us - Saturday mornings at 0930 Pacific time
on 10137 KCs (MARK at 10138575 & SPACE at 10139425)
(alternate frequencies 7087 & 3607).

 Any comments or additions?
EMAIL me...        Dave Ross     N7EPI

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