The relay is just an electrically operated single pole double throw switch - nothing more.  So, you can use it to connect one of anything to either of two other anythings.  For HF, insertion loss will not be a consideration.  But - why use a relay at all?  If you can locate a manually operated coax switch where you can easily reach it, a relay is overkill.  Coax relays are generally much more expensive than they were several years ago and one that will handle 1500W on HF with a 12 volt coil can be $180.  Other coil voltages may be less and you can often find coax relays with odd coil voltages (24 or 26V DC) on eBay for considerably less.  You may also find that a relay with BNC connectors is less than one with SO-239 connectors when buying one surplus.  Regarding radio damage due to human error: a dummy load is a good idea, but I'll bet that there aren't any modern transceivers that would be damaged by operating them into no load.  Transceivers almost all have protection circuitry that reduces the output power with a high SWR as you'd have with no load connected.  Most begin folding back power with an SWR of 2:1 or even less. 

I do use a coax relay on the output of my 1500 watt amplifier to switch between the antenna system and a dummy load.  Some amplifiers do NOT have SWR protection and accidentally operating them into an open circuit can cause real problems. 

73, Floyd - K8AC

 I just checked their website and it's available there for download.

You might want to try Triplett.  I needed a manual for a sweep generator of similar vintage a few years back and they had it in their archives.  Sent it to me at no charge.

Working 'em by the numbers for the USA in consideration of geography may have made sense in 1970, but makes little sense now.  For a significant percentage of USA stations today, the number in their call does not reflect the "call area" as once did.  This DXpedition seems not to understand that.  Seems like specifying the geography, such as, West Coast, Southeast, Northeast, etc. would be more productive.

73, K8AC ( residing in "4" land)

To QRPNEW: I just set up a test to get an idea of the right answer to your question.  I used a K1EL WinKeyer USB, set for 50 WPM using their software, and I'm just assuming that their speed calibration is correct - could be off.  I then keyed one transceiver (Drake TR7) with the 50 WPM keyer while monitoring the signal on a second transceiver (Tentec Orion II) whose audio was being recorded by Adobe Audition software to allow me to look closely at the waveforms.  Running with a weighting of 50, which should result in an equal length of dit to space, dashes were observed to be 70 milliseconds long and dots were 23 milliseconds long - just about right. 

Someone else measuring the same thing would find that the numbers differ depending on a lot of things, such as waveform shaping in the transmitter or QSK performance.  For measurement purposes, I chose to start an element with the first indication of a rise from noise level and stopped the element length just before the level returns to zero.  In practice, the wave shaping in the transmitter affects the dot to space ratio a lot.  In my test, a visual inspection of the waveform would suggest that the keying was too "heavy", while in fact it sounded just right.  This particular transmitter was modified to eliminate key clicks and the resulting "long tail" is what affected the dot to space ratio. 

73, Floyd - K8AC

I can see why some folks are reluctant to ask questions!  The truth of the matter is that it would be difficult for anyone to answer your question without knowing a lot more about your CW signal.  For example, how is the weighting adjusted on the device that is generating the CW?  For academic purposes, I suppose one could assume a weighting that results in a dit being just as long as a space and a dah being three times that long.  But, having measured a lot of CW signals (mine and others), I can tell you that very few keyers are producing that ratio.  At least one high end transceiver produces dits and dahs that are substantially below the ideal ratio to the point of sounding clipped, when adjusted for a supposed perfect ratio.  So, the question that you think is so simple is not simple at all, at least it isn't if you are interested in any sort of accuracy.

73, K8AC

Not nearly enough information given to hazard an intelligent guess.  Are you using a com port for the CAT interface to the Pro III, or a USB/serial converter cable?  In whatever software you're using, did you specify the Pro III address properly?  If you're using a USB/serial converter cable, is it powered from one of the interface lines, such as request-to-send (RTS)?  If so, do you have that line specified as always "UP" in the software configuration?

Smells like a troll, but deserves a response.  Both petty theft and grand theft are crimes.  The only difference is the dollar value involved.  Operating LSB on 7.126 is not just poor practice - it's a violation of the rules we operate under.  It's not up to us to judge which rules we choose to follow, nor decide which violations might cause the greatest problems.  It's a good idea for everyone to follow the rules as they're laid out.  I'll wager that every one of those who responded on 7.126 did so out of ignorance, not because he thought he could get away with a petty violation.  My post was an attempt to elighten some who either were not aware of the fact that 7.125 is the lower band edge for SSB operation in the USA, or that their LSB extends far below the carrier frequecy their display reads. 

If it were me, I wouldn't be using a Johnson T/R switch for SSB use.  There's no relay in the Johnson switch and as someone else mentioned, if there is current flowing in the transmitter final when you're not talking, you'll hear that as a high white noise level on receive.  I believe the HT-37 does have a switched output line on the connector on the rear panel, so you could use that to control a relay used to switch the antenna between transmitter and receiver.  We used to use a Johnson T/R switch for CW and that eliminated having to throw a switch when going from receive to transmit.  However, since there was generally no CW sidetone available at that time, we typically listened to our own sending on the receiver, which usually meant turning down the audio manually to save your ears.  Another common problem with the T/R switch approach was "signal suckout" which could reduce the signal level heard in the receiver.  T/R switch manuals often advised you to change the length of interconnecting coax to minimize or eliminate that.  Check DX Engineering for a box that meant to do the antenna switching in a properly timed fashion for old separate rigs.  There have also been articles in QST over the years for home brew versions of that.  I built one here years ago and it made using the old rigs on CW a pleasure.

Spratly has been cancelled.

Are the TV and Blu-Ray player SONY?  Turning on the SONY player will also turn on the TV if it's a SONY, and I think turning the player off then turns off the TV as well.  The HDMI cable probably serves as the com link in that case.  I'd put my money on the player being the source of the problem.  I have the SONY setup here, but have never had a problem with 1500W from a nearby yagi.

I use a FlightCom Denali - a lightweight aircraft headset with mic.  They're made to wear for extended periods, and you can often find them in great condition on the used market.  Check out sites where pilots buy/sell such things. 

But - you could miss that question and still pass the test!  And, just what is meant by "exactly at the edge..."?  A reasonable person could say that 7.126010 isn't exactly at the edge.  Just what the lower limit is in this case depends upon one's voice characteristics, how high you have the processor set, etc.  In some cases, 3 KHz might be too close, but in nearly all cases, just over 1 KHz assures that a significant portion of the sideband is outside the limit. 

I was amazed this morning listening to VK7ZX sitting on 7.126010 running US stations at the rate of about 100 per hour.  Transmitting on that frequency on LSB results in radiating quite a bit of sideband power well below the 7.125 limit for US stations.  The transceiver frequency reads the carrier frequency and a bit more care needs to be exercised when operating LSB near a bottom band edge or USB near the top edge. 

Way to go, Joe!  That's a far better rig than many of us had starting out decades ago, and our antennas weren't any better.  At that time, my ham friends were mostly broke teenagers and we got great pleasure out of making simple and inexpensive things work.  One of my more memorable QSOs happened while I was testing my Heathkit DX-20 transmitter using what we all thought was a decent dummy load - a 100 watt lightbulb on a piece of coax.  To my surprise, another Novice 300 miles to the west of me began calling me and told me I was 579 using the lightbulb antenna.