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Author Topic: ANTENNA COUPLER AT BASE OF 43' VERTICAL  (Read 4474 times)
K3MOV
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« on: May 12, 2011, 11:40:51 PM »

I have operated my Zero Five 43' vertical for about five years using an MFJ 998 Tuner in the shack.  After thinking and talking about it for almost five years, I now want to move the tuner to the base of the antenna.  I have a couple of quick questions: Has anyone used a tuner such as the 998 ouside?  If so, what precautions did you take to protect it from the weather as it is really meant  to be used inside?  I use a PROIII and Ameritron ALS 600 amplfier.  Do you think I would be better off using a tuner manufactured to be used outside such as the SGC 235?  It is very pricey and I read somewhere that it does not like any vertical shorter than 50'.  I have a pretty good radial field of 40 radials about 45' long.

Thanks for any constructive input you can offer.  73, Tom K3MOV
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K3GM
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« Reply #1 on: May 13, 2011, 04:31:49 AM »

http://www.eham.net/ehamforum/smf/index.php?topic=69673.0;wap2
http://forums.qrz.com/archive/index.php/t-256481.html

Obviously you understand that the 998 was not designed for outdoors use.  I'd be particularly concerned about operation at high humidity levels.  As the threads above suggest, you can put it in an enclosure.  But unless it's purged with dry nitrogen, and then hermetically sealed, you're going to have some level of moisture inside which could promote dendritic growth on the PC board and possible flashover or failure.  A plain old enclosure like a Tupperware box will also "breathe" over time, and when it does it will exchange air inside with air outside.  So personally, if I couldn't seal it completely, I think I'd use an enclosure that would allow free exchange of inside and outside air so it wouldn't promote sweating.  It sounds like a great idea, and you would probably see better performance from your antenna system.  But, I would question its long term survival being outdoors.  Perhaps a trial run on a nice day with the 998 located at the base of the antenna would help you decide if it's worth the trouble of fabricating an enclosure.
« Last Edit: May 13, 2011, 05:04:25 AM by K3GM » Logged
AD5X
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« Reply #2 on: May 13, 2011, 04:39:28 AM »

Tom - Neither the SG-235 nor the MFJ-998 autotuners can tune a 43-footer on 160 meters, unless you add an external series inductor (see the "Articles" section at www.ad5x.com where I did this with a MFJ-927).  However, both tuners will tune 80-10 meters fine (43-foot vertical).  The SG-235 is also only rated for 200 watts continuous, 500 watts PEP.  I'd recommend using a MFJ-994B mounted outside as it will easily handle the power of the ALS-600 in this application.  The MFJ-994B is also much smaller than the MFJ-998 and so should be easier to find a box for it.

Rumor has it that MFJ will be releasing outdoor packaged versions of both the MFJ-994B and the MFJ-998 shortly.  Also, the Elecraft KAT500 autotuner is supposed to be availble in both indoor and outdoor packaged versions (expected release is sometime this summer).  So it might be worthwhile waiting a few months to see what is available.

Phil - AD5X  
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ND6P
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« Reply #3 on: May 13, 2011, 08:14:26 AM »

Just tossing out an idea here.

If you were to build a matching unit at the base of the antenna to bring down the SWR on your favorite bands, you could leave your autotuner inside.  This would mean taking a trip out to the antenna to change bands.

Jim, ND6P
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K3MOV
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« Reply #4 on: May 13, 2011, 08:51:17 AM »

Thanks for all of the useful input, gents.  It appears that once again my procrastination may have paid off.  With newer outside models on the drawing board and coming down the pike, I guess I can wait a little longer, having put this off for five years already.  In the meantime, I'll just stick with what I've got as is allows me to work the world with no problem.  But since the day of my original installation, I knew sooner or later I would want to try the increased efficiency of the coupler at the base of the vertical.

Phil, thanks for the info on 160.  I have, of course, read all of your articles and reviews.  At one time wasn't the Chinese company supposed to come out with CG 800 which could be used outside?  I read a couple of good reviews about it but then it sort of disappeared.

73, es tnx agn, Tom K3MOV
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N3OX
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« Reply #5 on: May 13, 2011, 06:08:39 PM »

If you were to build a matching unit at the base of the antenna to bring down the SWR on your favorite bands, you could leave your autotuner inside.  This would mean taking a trip out to the antenna to change bands.

Naaaaah...

http://www.n3ox.net/projects/lowbandvert
http://www.n3ox.net/projects/sixtyvert
http://www.n3ox.net/projects/stepperswitch

Going outside to change bands isn't realistic for me.  I change bands every few minutes usually, when I'm running around the bands searching for DX.  As of the last iteration above, I don't even have to touch anything.  My antenna automatically follows me around the bands.
 
It was a lot of work but I'm glad I did it.  Easily handles 500W-600W (all I've got) and probably would be fine at full legal at least on 80, 40, and 30.  Don't use it above 30.  Doesn't quite handle 500W on 160 because the fierce voltage is enough to arc that switch.  

If I were trying to use this on many more bands I'd probably go with an autotuner but the set-and-forget setup is good for what I'm doing.

That said I think I'd probably just build a trap vertical if I did it again Grin
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W6RMK
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Posts: 649




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« Reply #6 on: May 13, 2011, 09:12:35 PM »

Just tossing out an idea here.

If you were to build a matching unit at the base of the antenna to bring down the SWR on your favorite bands, you could leave your autotuner inside.  This would mean taking a trip out to the antenna to change bands.

Or, build several matching networks and use a remote relay box of some sort to select them. The matching network would "get you close", and the tuner in the shack does the fine tuning.  Saves the trip outside
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WA7NCL
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« Reply #7 on: May 15, 2011, 05:32:32 PM »

I had a buddy who put one of the marine type SGC tuners inside a plastic dog house to protect it from the direct rain and other elements.  The plastic enclosure of the SGC kept the bugs out.  The system worked well with a few radials and a vertical piece of wire run up a small tree about 40 feet.  Maybe you could try some thing like that.
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KD0NFY
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« Reply #8 on: May 16, 2011, 11:12:30 PM »

Although it sounds like you've already got this sorted out, here's my take on a tuner at the feed point.

I use a horizontal loop with an SGC 230 tuner just shy of the feed point.  I run about 20 feet of window line from the tuner to the antenna feed point in order to keep the tuner out of the weather.  My longest contact so far (just licensed last year) has been a little over 6000 miles to Nigeria on 17 meters with 100 watts.  I routinely work stations around 5000 miles away on 20 and 17 meters.  I don't think there's any way I could do it with a tuner in the shack because of coax losses.  But that tuner is only rated for 200 watts.  Still might be worth messing with if you could find a deal on one though and band hopping is quick and easy. 
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KF6A
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« Reply #9 on: May 17, 2011, 01:36:05 AM »

Although it sounds like you've already got this sorted out, here's my take on a tuner at the feed point.

I use a horizontal loop with an SGC 230 tuner just shy of the feed point.  I run about 20 feet of window line from the tuner to the antenna feed point in order to keep the tuner out of the weather.  My longest contact so far (just licensed last year) has been a little over 6000 miles to Nigeria on 17 meters with 100 watts.  I routinely work stations around 5000 miles away on 20 and 17 meters.  I don't think there's any way I could do it with a tuner in the shack because of coax losses.  But that tuner is only rated for 200 watts.  Still might be worth messing with if you could find a deal on one though and band hopping is quick and easy. 

Don't take this the wrong way but being licensed since last year hardly qualifies you to comment on what it takes to work DX. 5000 miles is easy on 20m, I used to do that daily running HF cw mobile while driving to work using just a hamstick and 100w.
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KD0NFY
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Posts: 75




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« Reply #10 on: May 17, 2011, 08:00:38 AM »

Although it sounds like you've already got this sorted out, here's my take on a tuner at the feed point.

I use a horizontal loop with an SGC 230 tuner just shy of the feed point.  I run about 20 feet of window line from the tuner to the antenna feed point in order to keep the tuner out of the weather.  My longest contact so far (just licensed last year) has been a little over 6000 miles to Nigeria on 17 meters with 100 watts.  I routinely work stations around 5000 miles away on 20 and 17 meters.  I don't think there's any way I could do it with a tuner in the shack because of coax losses.  But that tuner is only rated for 200 watts.  Still might be worth messing with if you could find a deal on one though and band hopping is quick and easy. 

Don't take this the wrong way but being licensed since last year hardly qualifies you to comment on what it takes to work DX. 5000 miles is easy on 20m, I used to do that daily running HF cw mobile while driving to work using just a hamstick and 100w.

Thanks for the tip.  I'll take down my loop antenna and replace it with a hamstick and try to work DX.  It's nice to have help from someone that's really qualified. 
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K3GM
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« Reply #11 on: May 17, 2011, 09:17:04 AM »

Don't take this the wrong way but being licensed since last year hardly qualifies you to comment on what it takes to work DX. 5000 miles is easy on 20m, I used to do that daily running HF cw mobile while driving to work using just a hamstick and 100w.

...I'm sorry, but I think I missed your comment to the original poster...... What was it again??

Keep posting, Harry.
« Last Edit: May 17, 2011, 09:18:56 AM by K3GM » Logged
K5USF
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Posts: 82




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« Reply #12 on: May 17, 2011, 12:24:03 PM »

My MFJ-998 is in a NEMA enclosure.  It has 2 small bug proof vents.  I ran a Z11Pro2 in a lowes outdoor box (without vents) for almost 2 years and the unit looks and operates like new.  It worked in summer rain, 110 degree temps and this past winter at -5F.  Of course, I am in the desert.  But, we do get summer monsoon rains with humidty from the end of June through August. 
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K3MOV
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« Reply #13 on: May 17, 2011, 08:33:44 PM »

K5USF... can you give me some specifics on your NAMA enclosure?  Tnx es 73, Tom K3MOV
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K5USF
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« Reply #14 on: May 18, 2011, 09:11:15 AM »

I bought this one:

http://store.solutionsdirectonline.com/am2068-nema-4x-fiberglass-enclosure-with-lift-off-screw-cover-20x16x8-p96.aspx

It meets or exceeds the following standards:

UL Types 1, 2, 3, 4, 4X, 12, and 13
• CSA Types 1, 2, 3, 3R, 4, 4X, 12 and 13
• NEMA Types 1, 2, 3, 3R, 4, 4X, 12 and 13
• IEC 60529 Type IP66
• Compliant with RoHS directive (Restriction of Hazardous Substances)


I also bought the 4 dollar ventilation kit.

You may be able to go one size smaller on the box.  I drilled a hole for a coax bulkhead connector.  Then drilled two holes for stainless steel bolts (1/4 inch) and wingnuts.  I put the bias tee in the box and pulled the power off inside the box.  The two bolts are for the radials and the vertical.  Also, I used a pigtail (coax to two wires) in the box from the tuner ANT to the two bolts (radials and vertical).  I added a third bolt for DC ground.  But, the tuner seemed to work much better without the DC ground.  My other bias tee in the shack does not have a on-off switch, so I added one.  This comes in handy when changing bands because the tuner at times needs toggled off-on to "wake up."  There is a picture on my QRZ site.

I did place alot of rice in a womans stocking and put that in the box to help absorb moisture.  Thats about it.


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