The AM Forum

I'm pairing up my new K7DYY Super Senior transmitter with an old Kenwood R-599 receiver. I only have one antenna, and I want to use it with both the new AM setup and my old SSB rig. I have a spare coax switch, a CO-201 that supposedly shorts the unselected input. I've never run two rigs on one antenna before, and I want to make sure the rigs won't nuke each other. Will the CO-201 provide enough isolation between the rigs to prevent any damage?

Bobby Dipole ND9B

Whatz a CO-201 switch? Company? Picture? Specs?

Dawia 2 way switch with so-239 connections  dc to 600 mhz good for kw cw..

Maybe he means this one labeled Jetstream:

(http://www.jetstream-usa.com/images/co201.gif)
Their catalog: http://www.jetstream-usa.com/jetstream.pdf

Probably better to connect and disconnect the antenna.  You should be disconnecting the antennas from your rigs when they're not being used.

Fred

This is "The Other Fred" and yes manual connecting might be safer and this is lightning season now.......That sinking feeling rushes in when that surprise thunder storm happens and you're at work or on the road....."Did I disconnect my station from the antenna last night?"

I have made it a "force of habbit" to spin off all of the antenna connectors if I'm not in the shack. Winter, summer, no exceptions. This "force of habbit" totally eliminates that "sinking feeling" when I'm not home.

Since I have owned this house (25 years) I have taken 3 lightning hits! ! ! ! ! !  

Yes this is the switch. I always disconnect the antenna at the entrance to the house using an MFJ feedthrough panel when a storm is forecasted.

Bobby Dipole ND9B

  I have had more "Brain Farts" dealing with the 2 antenna's one one
rig.  IE: my Ft-857D, it seems so un-natural even after 3 or 4 years.

/Dan

[/quote]
I have made it a "force of habbit" to spin off all of the antenna connectors if I'm not in the shack. Winter, summer, no exceptions. This "force of habbit" totally eliminates that "sinking feeling" when I'm not home.   
[/quote]

I don't think that the question had anything to do with disconnecting the antenna during a lightning storm.

I just realized that I could measure the switche's isolation with my RF generator and the S-meter on my rig. I cranked the generator up on 20M (the highest freq band I use) for a reading of 60 over 9, then flipped the coax switch. The S-meter fell all the way to the end of it's range. The isolation must be at least 100db if the meter is right. I see no problem now.

Bobby Dipole ND9B

I have never experienced any failures for the last 4 years and I use a 6 position MFJ coax switch. When I operate I don't disconnect equipment that is not in operation. I simply set the switch to the gear I intend on using, leaving all other gear connected to the switch. Whether you use this method or not is entirely up to you.



73s
Mike

Buddy.  Go for it.  That switch grounds the other side and becuase that switch is on the other side of the TR switch in the SR.  You are ok.

C

Many coax switches have poor isolation especially at upper bands and could cause damage, the B&W, MFJ (old ones anyway), most CB are among the worst. Not sure if the Heath grounds unused positions.

I use Bird, Daiwa, Dow-Key and a few others that are well constructed and have high isolation to allow even 1500W safe passage.

Carl

Very true.  In this case, He is just switch his Receiver on the Reciver output of the SR.  So no power is here.

The One of the best coax switchs in my opinion is the Blue MFJ unit. I have had most major brands. The Alpha delta is not nearly as good as the MFJ.  The Bird do not short.  The diawa and others are just light duty.

Inside the Alpha is a thin contact rail.  If there is not perfect alignment, The switch arcs out.  I have had two fail in AM use.  The MFJ switch has very large contacts like a big relay.  Those contacts are at least 10 amp each.  There is a positive contact.  opened one up and looked inside. There is no comparison in quality of the switch. Its rare to find a super MFJ product but they are out there!

Where the Alpha delta failed for me was when I had two antennas in the near field.  I would transmit on the inverted V and the RF from that antenna was couple to the L outside on the same tower.  That RF would shotgun down the L and into the Alpha delta.  It was not long before that Alpha delta was shot.  The MFJ just puts that current to ground and never failed.

C

If you use a dummy load for tuning up, etc, you might consider putting together a manual transfer switch. It is a DPDT RF switch with four ports. There are relay powered ones on the surplus market for many $$$. You can set it up so that either radio connects to the antenna or alternately the dummy load. IF you ever operate with both radios powered up, you don't have to be concerned about transmitting in to an open or shorted line. IF you are mechanically inclined, you could fashion a linkage between two SPST switches and "T" the outputs, or just build one up using a quality HV ceramic DPDT rotary switch with 10A contacts, a small bud box, four Coax connectors of your choice, and buss wire. You may not get isolation of 100dB, but it will suffice for your HF application if you keep the wires short and perpendicular to each other.

If you go the "Roll Your Own" route, you might consider getting a multiple pole switch with at least as many positions. For example, a three pole three position switch would allow you to select which one of three radio went to the antenna while the other two went to one of two dummy loads.  

Bobby Dipole,
Manually switching between TX and RX with an ANT switch is OK but you should also consider putting the RX in standby when the TX is keyed.  If you can rig up a relay to close when the TX is keyed and tie the relay contact closure to pins 7 and 16 of the connector on the rear panel of the RX you will put the RX in standby thus saving the front end and not have to worry about coax switch isolation. At amateur power levels the R-599 should be OK fine.  You could take it a step further and create a TX/RX relay so you don't have to mess around with manual control of a coax switch too.  

R-599 connection info here: http://www.n6wk.com/kenwood/R-599D%20Operating%20Manual.pdf

See page 18 of the document of the above link for connection info.

Bob, Been using cheap and dirty Heath 4-pos coax switch (one that shorts unused connections) with a Ten Tec Paragon, Jupiter, Homebrew pair of 4-400's (w/R-8A RX, or a Drake TR-7 rx, or various other boatanchor rx's), and the Gates BC-1G BC TX at 350 Watts (and an R-8 RX).  Never have had a problem injuring another piece of equipment. 

The lightning issue, of course, is a horse of a different color and that requires the actual antennas be disconnected from any equipment (plus lots and lots of other precautions)

73 Jeff W9GY

You are correct! There was a little diversion about remembering to disconnect all the extra equipment with Summer, and even now, storms starting up.

I would suggest getting one nice DOW T/R relay for the AM station beings that you gotta separate TX and RX and connect the common or antenna port of the DOW relay to PORT A of the MFJ unit. The SSB station or transceiver has it's own T/R relay. A coax jumper would go to the B port of the MFJ unit.
Select A for AM operation and B for SSB.
The general thought has been that the isolation should be ok.

Just noticed:::: The SUPER SENIOR has a phono jack for the Receiver. Does the Senior have it's own T/R relay??? I don't like the phono jack though, but should be ok.

Have used the Diawa two position switch in the die-cast housing.  It looks very similar to the MFJ pictured.  Seems robust,  and this switch does ground the unused port.  Have never looked inside,  but these work very well.  I have not had the guts to two High-Tap rigs on each port,  but have been wondering about doing just that.

IMHO,  the Bird,  while does not ground the unused port/s,  the center conductor of the N connector is the switching element.  This switch,  has only one center pin,  which is moved to the selected connector (for the single pole version).  Bird also makes Transfer Switch version  which has two center pins,  and selects two ports of four.  I cannot see how these would need any grounding mechanism  of unused ports.

Have a couple of these Bird transfer switches here.  I do not like putting N connectors on cables,  or using N-PL-259 adapters,  but seems to me that the Bird siwtch would be a good solution.  Any comments?  Thanks,  Vic

Yes the Super Senior has it's own T/R relay. It also has an output for muting the receiver during xmit. I actually like the idea of the phono jack for the receiver. It makes it less likely to get the two outputs reversed! (Hey, it happens. I've accidentally reversed the in/out on my linear several times.)

Bobby Dipole ND9B

My Hunter linear uses a RCA jack for the RF input, works fine. However, finding a male RCA to female UHF connector was a little difficult. When I first got on AM, I had an FT-101 that I used for transmitting and an IC-718 for receiving, and switched the two with a coax switch. If I would've known then what I know now, I could've set the Icom to receive only, then ran an RCA cable between the linear keying jack on it to the PTT jack on the yaesu, and used the 718 to key the yaesu, which should've worked and it would've muted the Icom, then either used the coax switch to switch between transmitter and receiver or used two antennas, one for each rig.

What was the question?  Oh yea.  That switch will be fine.

N connectors are available in crimp now but I still use USA made hamfest priced adaptors on the two 10 position Bird Model 74's I bought at hamfests in the 60's for around $20 each. They have handled everything Ive run thru them and get taken apart for a cleaning every 20 years or so.  I like that pull-turn-push solid feel.
For transfer I use Dow-Key and Transco relays.

Carl

I only suggested muting the receiver because I have several rigs on an ANT switches.  When I fire up the 813 rig I peg the S meter on the FT102 so I disconnect it because I have no way to mute the receive section but my stand alone receivers I mute to protect as much as possible even though the ANT switch is a shorting type. There's enough RF in the system to get to the receivers.

N- connectors are great for outside use. They are water proof and provide a more stable 50 ohm than the PL259's.

And ok on the phono jack. You are right on when there can be confusion between TX and RX and you are trying to connect in a dark rack.

The antenna switch seems to be a decision you will have to make. MFJ is cheap copies of branded stuff. Sometimes their items are just as good as the higher priced stuff. And you know what??? You see that little Antenna Analyzer EVERYWHERE...the entire whirl has them!!! It's not NIST quality, but gets the job done. I wouldn't be without one.
Fred

I figure even with 100 dB isolation, you will still get a few mV of signal into the unselected rig. In my case, the unselected rig will always be off, so no problem.

Bobby Dipole ND9B