K1TTT Technical Reference

Subject: 
        Remote Coax Switch Redux
   Date: 
        Thu, 28 Nov 1996 10:47:49 -0500
  From: 
        jbmitch@vt.edu (John Mitchell)
    To: 
        cq-contest@tgv.com


Many thanks to all who responded to my request for experience with remote
coax switching.  Below are the responses received.
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>I've used the RCS-8v for several years with no problems (actually use 3 of
>them).  Cable run of up to 500 ft, in my case.  Have used scraped spools of
>cable that I got for free.  I'd be interested in hearing the comments about
>how well the rsc-4 works at a 1000 ft.  Gee, 1000 ft of coax-sure hope that
>isn't to the 10 meter antenna (hi-hi).
>
>73 WA0ETC
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>I realize you said you don't want control cable, John, but the Top
>Ten Devices boxes are great and totally automate antenna switching. 
>They do have a web site http://www.qth.com/topten
>=====================================
>Beryl D. Simonson  K3AR  (formerly KE3GA) Frankford Radio Club
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>Hi John,
>Yes please summarize.
>I am going to install a remote coax switch myself but my problem is not
>the distance. I need a switch to be reliable at very low winter
>temperatures (about -40F).
>Thank you.
>73! Vitaly (VE6JO)
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>I use the RCS-4 at a distance of about 200 ft. It works ok
>but the box itself affects the antenna's SWR and resonant freq.
>(I assume because of the inductance at the remote box needed
>to extract the control voltage). You may want to consider
>this. I plan on replacing it with a unit that uses a separate
>control line.
>
>73
>Kris N5KM 
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>I can only provide an anecdotal response.
>
>When I planned my treetop Force 12 installation in early 1994, I needed
>to switch between the two feedpoints of a F12 DXer, a 30m rotary dipole,
>and, ultimately, a 160m wire dipole whose center was near the same tree.
>Tom Schiller, N6BT recommended the Ameritron unit with the external
>control cable. Since that meant another expense and hassle, I asked him
>why he would not recommend the RCS-4. Tom, in his typical laconic
>response, said "because it won't blow up." He had lunched an RCS-4.
>-- 
>Garry Shapiro, NI6T
>Editor, The DXer
>newsletter of the Northern California DX Club
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>John,  mine is not a "long distance" but maybe of interest:
>I use the FCS-8V, which requires the additional run of cable.
>I feel that is worth not putting a cap. in the middle of my coax line.
>
>The other point is:  I've modified my 8V.  I added 3 micro switches
>from radio shack just right of the selector knob.  These are 
>connected to 1,2,3.  I can turn those relays on via the switch.
>Hence it is possible to feed four antennas at once.  The fourth
>being selectable between 4 or 5 via the front control.  Well you
>can figure out the combinations, but it does open up the possiblity.
>In reality two at once is proably all we'll use.
>-- 
>73 Robert  W5AJ  w5robert@blkbox.com   
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>I just built a control box for an 80-meter wire array, which I'm controlling
>through 350 feet of 4-wire telephone cable.  My box uses the same basic
>scheme as the RCS-4 and the Heathkit equivalent, and has no trouble
>switching through those #20 or #22 conductors, so I'm pretty sure you'll
>have no trouble using your hardline (which I do with my Heath switch on 200
>feet of hardline and 50 feet of RG-213).  See the copper wire table in the
>Handbook for further reassurance.
>
>73, Pete Smith N4ZR
>n4zr@contesting.com 
>West (bigawd) Virginia
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>I use an RCS-4 for switching my slopers and have had no problems.  It's
>about 200' out from the shack.  
>Power-wise: I've shoved 1.5kW threw it for years. 
>Temperature-wise:  Worked at -42 and +117. 
>Distance problem:  I don't know what the power requirements are so I can't
>really say if 1000' will be problem....but think of it this way - The center
>conductor and shield are equivalent to pretty large wire.  The voltage drop
>shouldn't be too great since the switch current can't be all that high.
>
>Have fun.
>
>Gary K7FR
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>     I have a similar situation although with several verticals.  If
>you could share your findings it would be greatly appreciated.
>
>73 - Doug - W2DR
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>Check out the Dunestar 808....new and will operate reliably at 9 VDc if
>you have that much drop.
>
>www.dunestar.com
>
>Jay WX0B
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>I designed the RCS-4 and 8V, as well as some switches for other companies.
>
>The RCS-4 will work with up to 30 ohms or more of loop resistance in the
>cable, the RCS-8V with 60 ohms or more. But the RCS-8 requires a seperate
>control cable but it can be cheap multiwire telephone cable.
>
>The RCS-8V will handle 8-10 kW for long periods of time ( the weakest link is
>the connectors, not the relays), has excellent return loss and port to port
>isolation up to 350 MHz, and a great service history.
>
>The RCS-4 is only safe to 2 kW and good to 30 MHz.
>
>73 W8JITom
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>John, I am using the RCS-4 and have been for 4 1/2 years.  I am extremely
>pleased with it.  My tower is located 250 feet from the shack.  I buried
>RG-9B, originally, for the full length of the 250 feet to the tower.  I
>later buried 7/8" hardline.  In both cases, the RCS-4 worked beautifully.
>I am using an Ameritron AL-1500 with the 8877 in the final.  It puts out
>as much power as it is legally possible to do.  (In fact, I have to watch
>the input closely because it can produce 2500 watts with no real problem).
>The RCS-4 has stood up to that legal output very nicely.  I do make a
>concession at the tower.  I put a plastic electrical connection box (it
>has a particular name and is about 12 inches wide, 6 inches deep, and
>16-18 inches high.  It is completely waterproof.  I cut two holes (about
>2" in diameter) for the incoming cable and the outgoing cables.  This
>serves to keep the RCS-4 relay box out of the weather and it does not
>rust, as a result.
>
>My personal opinion is that it is the only way to go.  My antennas are
>400 feet from the shack (tower is 140 feet) and 4 separate lines of
>hardline of 400 feet in length is unthinkable.  It is my opinion that
>you will be pleased.  73, Rod. W5HVV
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>       Just wonder if your aware of the Dx Engineering swithch box.
There at 618 Spaulding, Brownsville, Or., 97327 . Its heavy duty and
uses rotor cable for control of the 5 positions on the switch. Their
phone number is: 503-466-3138. This switch has sealed relays and a metal
cover over the outside unit. The Ameritron does not ! I used the RCS-8
for about 4-5 years but think I was getting RFI thru the plastic relay
cover. I just bought the Dx box this Aug and it sure beats the
Ameritron. The Dx box sells with shipping for less than $200.00 . Its
well worth the extra $. Rotor cable lists in their catalog for .18 per
foot. (#22) It says you can use that cable on runs 1000 feet away.
>Carl KF8VW
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>At my old QTH I had a half mile of hardline to a woods where I installed
>three beverage antennas. I "piggybacked" DC on the hardline so I could
>select any of the 3 beverages. On this and other long runs I first tried
>using 12 VDC relays but occasionally the voltage drop through the isolation
>RFC was great enough to cause problems. So I switched to 24VDC relays. On
>the long runs I will actually feed about 40 volts into the line and then
>there is plenty at the other end-- 25 or 30 volts or so. Also, surplus 24V
>relays tend to be cheaper since they are in less demand.
>
>All my relay boxes are homebrew. I use the same basic technique for beverage
>switching and for transmit antenna switching. The relays are mostly Potter
>and Brumfield, open face, with 10 amp contacts. These handle 1.5 KW without
>any problem (no hot switching, please!). At the feed end there is an RFC
>(typically 1mh or 2.5 mh) to isolate the feedline from the power supply, and
>a capacitor (typically .01 mf or .001 mf) in series with the feedline to the
>RX, for isolation. At the antenna end, another capacitor isolates the
>feedline from the antenna. And another RFC isolates the feedline 
>from the relay coil.
>
>For Beverage antennas the capacitors are usually disc ceramics. For
>transmitting I usually use big old Mica capacitors from WWII, picked up at
>hamfests!
>
>If you use the Ameritron you might have to raise the conrol voltage to allow
>for the voltage drop in the feedline. 
>
>My homebrew relay boxes have worked for 10-15 years with few problems. The
>boxes I put them in are "weatherproofed" but not water tight; in fact I put
>a small drain hole in to allow moisture to escape. If not used for extended
>periods -- such as over the summer -- the contacts may oxidize a bit and I
>have to switch them on/off a few times to restore normal operation.
>
>73/Jon AA1K
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>I've used an RCS-4 for several years now.  It always switched reliably, even
>when cold.  The problem I had was that it crispy-crittered on 160.  Not
>enough choke or something.  The antenna had about a 2:1 SWR and I was
>running legal when it overheated.  I rebuilt it to separate the relay feed
>from the main coax.  I used a piece of old RG-58 to carry the switch
>voltages and it works fine.  I do know of several people who use the other
>model and use dirt cheap telephone wire (3 or 4 pair) to feed it and they
>switch just fine.  In short, if you don't have the 160 meter problem, it
>should work just fine, even over 1000'.
>                                        Dan KL7Y
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>I have no experience at runs over 200' but have some input into remote 
>switches.  I am presently using a DX Engineering 6 position remote switch.  I 
>have used a Heathkit remote switch that is identical to the RCS4 in the past.
>
>1.  The DX Eng unit is electrically sound and has had several years of use 
>with no problems.  The enclosure (a NEMA 3 box with a 2" knockout in the 
>bottom with a bushing for coax) leaves a lot to be desired.  I actually had a 
>squirrel's nest in the bottom of the switch complete with acorns.  The switch 
>requires a 7 conductor cable which I recommend (later).
>
>2.  The Heathkit switch was reliable but after awhile I could hear a slight AC 
>hum in the receiver directly traced to the switch.  No good!
>
>3.  I sometimes regret using a remote switch due to the fact that it precludes 
>the use of these antennas with more than one rig at a time.  If I redesigned 
>my station at least I would mount the switch at the bottom of the tower.
>
>4.  The cable that I am using is regular rotor cable (#22 & #18).  No heavy 
>gage wire is necessary due to the light load of the relays.  You can use 
>multi-pair telephone cable if you like, even at 1000 ft.  A voltage drop calc 
>may be necessary depending on the relays in the switch.  I did have a problem 
>with cable.  Squirrel's again.  They ate though the jacket and two of the 
>conductors about 15 ft up the tower.
>
>5.  One last thought.  I have bought several products from Top Ten devices.  I 
>don't have one of their remote switches but have seen pictures. Taking the 
>above comments into consideration I would recommend their switch.  If I have 
>to buy another switch, it will be a Top Ten!
>
>Dan
>AB4RX@MSN.COM
>
--------------------------End of  Response
Transcripts------------------------------------

Final Comments de IQ:  Nothing like this group to come forward with
excellent experience on any topic related to the hobby!  Many thanks again,
and I will take some time to digest all this and check out the Top Ten and
Dunestar sites. 

73,
John K4IQ