[TowerTalk] TowerTalk Digest, Vol 156, Issue 54
wosborne44 at gmail.com
wosborne44 at gmail.com
Wed Dec 16 10:03:02 EST 2015
Thanks Dave, that is very helpful.
------ Original Message ------
From: towertalk-request at contesting.com
To: towertalk at contesting.com
Sent: 12/16/2015 6:16:31 AM
Subject: TowerTalk Digest, Vol 156, Issue 54
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>Today's Topics:
>
> 1. Re: [Bulk] Fwd: WTB Rohn 25G tower insulator (Grant Saviers)
> 2. Re: [Bulk] Re: Reverse Fed Towers (Drax Felton)
> 3. Re: Reverse Fed Towers (Dave Thompson)
> 4. Reverse Fed Towers (n0tt1 at juno.com)
> 5. Re: Reverse Fed Towers (Chuck Dietz)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Tue, 15 Dec 2015 13:58:17 -0800
>From: Grant Saviers <grants2 at pacbell.net>
>To: towertalk at contesting.com
>Subject: Re: [TowerTalk] [Bulk] Fwd: WTB Rohn 25G tower insulator
>Message-ID: <56708CF9.8010200 at pacbell.net>
>Content-Type: text/plain; charset=windows-1252; format=flowed
>
>I have some white UHMWPE that was used as combo thrust and axial
>bearings in side arm rotators, sections are over 1" thick. All are
>pretty badly crazed and not quite cracked thru after 7 years in the OR
>"sun". I didn't make these, so I don't know the grade or supplier of
>the material but am cautious about the UV stability of UHMWPE as a
>result. I use black material where UV exposure is likely. TIVAR info
>on UHMWPE, many grades: http://www.bayplastics.co.uk/polyethylene.htm
>
>Generally, natural UHMWPE is not considered to be UV stable.
>
>I find it hard to machine to tolerance since it is so slippery and
>gummy. Very sharp, correct relief tooling is required. Otherwise it
>is a very useful material and cheap.
>
>Grant KZ1W
>
>On 12/15/2015 13:31 PM, Hans Hammarquist via TowerTalk wrote:
>> UHMWPE is available at Walmart (at all places). It's called "TIVAR
>>GRA0133002037" as sheet Stck, 12 In.x 24 In.x 0.500 In. @ $87.84.
>> Hans - N2JFS
>>
>> .
>>
>>
>> -----Original Message-----
>> From: Andre VanWyk via TowerTalk <towertalk at contesting.com>
>> To: towertalk <towertalk at contesting.com>; rcm <robrk at nidhog.net>
>> Sent: Tue, Dec 15, 2015 3:17 pm
>> Subject: Re: [TowerTalk] WTB Rohn 25G tower insulator
>>
>> I will use these if all fails. UHMWPE material will outlast
>>fiberglass in
>> the sun too.
>>
>> 73's
>> NJ0F
>>
>> -----Original Message-----
>> From: rcm
>> Sent: Tuesday, December 15, 2015 1:40 PM
>> To: towertalk at contesting.com
>> Subject: Re: [TowerTalk] WTB Rohn 25G tower insulator
>>
>> http://www.wb0w.com/tower_insulators
>>
>> On 12/15/2015 01:06 PM, Andre VanWyk via TowerTalk wrote:
>>> I am getting parts together for a 160m vertical, using Rohn 25G
>>>sections.
>> _______________________________________________
>>
>>
>>
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>
>
>
>------------------------------
>
>Message: 2
>Date: Wed, 16 Dec 2015 02:02:07 +0000 (UTC)
>From: Drax Felton <draxfelton at gmail.com>
>To: Peter Voelpel <dj7ww at t-online.de>, Grant Saviers
> <grants2 at pacbell.net>, <towertalk at contesting.com>,
> <wosborne44 at gmail.com>
>Subject: Re: [TowerTalk] [Bulk] Re: Reverse Fed Towers
>Message-ID:
>
><AA176A7399F20B16.91FC6671-6B2D-4ACA-9EBB-B6B6989B25D6 at mail.outlook.com>
>
>Content-Type: text/plain; charset=UTF-8
>
>It had no effect on that stuff when I did it. ??
>
>Sent from Outlook Mobile
>
>
>
>
>On Tue, Dec 15, 2015 at 1:26 PM -0800, "Grant Saviers"
><grants2 at pacbell.net> wrote:
>
>
>
>
>
>
>
>
>
>
>Curious as to how one manages all the rf induced into yagis, rotators,
>coax, control cables, etc when an antenna loaded tower is QRO excited.
>
>Also, how the same cables are decoupled from the tower at whatever
>levels are appropriate and what is done at the shack end if anything.
>
>Grant KZ1W
>
>On 12/15/2015 12:55 PM, Peter Voelpel wrote:
>> I use a system like that.
>> My tower is loaded with some yagis and 46m high at the top.
>> I feed it at the 25m level against a single sloping radial.
>> The inner conductor is connected to the radial, the shield to the
>>tower.
>> The connection point was simulated with EZNEC before and was right at
>>less
>> then 1m difference.
>> The antenna works perfectly well for me, SWR2 band width is about
>>200kHz and
>> fine tuning can be done at the radial.
>> It is also very good on receive, picks up much less noise then the
>> previously used ground fed T-vertical.
>> >From distances beyond 1000km it is already better then the 30m high
>> inverted-vee.
>>
>> For cq160 I usually add an inverted-L reflector for directivity to
>>VE/W.
>>
>> If you are interest I will email the EZNEC file.
>>
>> 73
>> Peter
>>
>>
>>
>> -----Original Message-----
>> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf
>>Of
>> wosborne44 at gmail.com
>> Sent: Dienstag, 15. Dezember 2015 18:46
>> To: towertalk at contesting.com
>> Subject: [TowerTalk] Reverse Fed Towers
>>
>> I have a tower that has a base that is in concrete and grounded. I
>> would like to make it a vertical without installing insulators. Has
>> anyone used elevated radials with reverse feeding, i.e., connecting
>>the
>> center conductor to the radials and the shield to the grounded tower?
>> I
>> see this in the ARRL handbook but I cannot seem to make a model of it
>> work. Any help would be welcome.
>>
>> Thanks,
>>
>> William Osborne--K5ZQ
>>
>> 270-205-9565
>>
>> Wosborne44 at gmail.com
>>
>>
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
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>> _______________________________________________
>>
>>
>>
>> _______________________________________________
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>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
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>------------------------------
>
>Message: 3
>Date: Wed, 16 Dec 2015 01:30:06 -0500 (GMT-05:00)
>From: Dave Thompson <thompson at mindspring.com>
>To: towertalk at contesting.com
>Subject: Re: [TowerTalk] Reverse Fed Towers
>Message-ID:
>
><7743743.1450247406879.JavaMail.root at mswamui-valley.atl.sa.earthlink.net>
>
>Content-Type: text/plain; charset=UTF-8
>
>
> Tom N4KG explained reverse feeding a tower in as I recall the May 1994
>QST.
>
>Tom does a good job of making it easier and yes, this is an elevated
>radial system. My main concern was not getting the radials far enough
>off the ground
>to avoid ground loss. ON4UN told me the radials needed to be 40 feet
>off the ground to be safe. There was a report by Christman released at
>Dayton in the early 1980's where he built a half wave vertical dipole
>that required isolators to be effective. K4PI looked at the design and
>told me it was too complicated.
>
>I built one using Spi-Ro short radials and using the MFJ 259 found that
>my 71 foot tower top loaded was matched at 1830 at 18 feet. A couple
>of others used the design to make effective 160 or 80 meter verticals.
>
>Dave K4JRB
>
>
>
>------------------------------
>
>Message: 4
>Date: Wed, 16 Dec 2015 07:23:40 +0000
>From: <n0tt1 at juno.com>
>To: TowerTalk at contesting.com
>Subject: [TowerTalk] Reverse Fed Towers
>Message-ID: <AABMHCFFAAKT2F2A at smtpout04.vgs.untd.com>
>Content-Type: text/plain; charset=us-ascii
>
>
>On Tue, 15 Dec 2015 17:45:39 +0000 wosborne44 at gmail.com writes:
>> I have a tower that has a base that is in concrete and grounded. I
>> would like to make it a vertical without installing insulators.
>> Has
>> anyone used elevated radials with reverse feeding, i.e., connecting
>> the
>> center conductor to the radials and the shield to the grounded
>> tower?
>
>Hi William,
>
>Yes, I did that this Summer/Fall, for a 7mhz antenna.
>
>Details, details.....
>I have a 70-ft BX tower and I installed
>12 radials (taking Rudy, N6LF's advice) that are
>insulated from the tower in groups of
>4 aluminum wires.
>
>BTW, it's interesting to note that our favorite
>frequency standard, WWV, has 9 radials
>on their vertical dipole antennas.
>
>The radials attach to a "buss" that
>is insulated from the tower legs with a short,
>ceramic "strain" insulator. The insulator
>is clamped to the tower via a small bracket
>and two SS hose clamps. Each "buss" is
>connected to a center insulator via 3 wires
>stripped from RG8 type coax and wrapped
>in tape to prolong their life. Each radial terminates
>in SS hardware on the "buss" to provide a mechanical
>connection. Each radial electrically connects to the "buss"
>via a homebrew wire clamp and a short copper jumper
>with AL/CU terminals.
>
>Connection to the tower is at 3 places via a 3/16" thick
>aluminum plate, triangular in shape, with 3 "arms" that are
>made adjustable in their length. At the ends of the arms
>I have a block of aluminum with slots cut into them that
>clamps onto the heavy sheet metal legs of the tower with
>a couple of SS screws. The top of the plate holds the
>center "beehive" type of insulator and the bottom
>holds a PVC electrical box. Inside the box I have a
>1:1 balun/choke wound on a FT240-61 (gasp!) toroid.
>
>The output of the choke connects to the beehive insulator
>and the supporting aluminum plate. The "leads" are reversed
>so that the radials are at DC ground via the shield of the
>coax matching section that feeds the input of the balun.
>The shield is grounded at the base of the tower. The
>matching section is the usual 1/4-wave length of two 75-ohm
>RG-11 coax in parallel.
>
>Up on the tower, with a antenna analyzer connected to
>the input of the balun, I found, as expected,
>no noticable change in input impedance when I shorted the
>coax shield to a tower leg. (Remember, the shield connects
>to the radials.) So, there's no issue with running the coax
>feed over to a tower leg (inside the tower) and then down to
>the base.
>
>About radial and tower lengths....I did start to model the
>antenna using EZNEC 6.0+. It was, for me, a waste of time
>because of all the angles of the tower, the 3 jumpers that
>feed the radial from the center of the tower, etc etc. A complicated
>mess! So, I started with a vertical tower length of 234/f and a little
>longer
>for the radials...something like 34 feet each. I expected
>that the vertical radiator length would be shortened
>by about 6-10%. It turned out that it was much more than that.
>I ended up about 7 ft shorter than the 234/f length. I ended
>up with the radials being about 33ft each.
>
>I measured the current in each wire on the
>"output" of the choke/balun and found that they were
>virtually equal at resonance. Per Rudy's white paper,
>(Google it) it's important to balance the currents in this antenna.
>
>The instrument I used was a homebrew current meter.
>I powered up the antenna with my MFJ-269 antenna analyzer placed
>right at the input of the choke/balun and the current meter
>probe was clamped onto each output lead of the choke/balun....
>obviously not at the same time.
>
>I attached some photos for you.
>
>Well, that's about it except to say, that I'm pretty sure that
>the radials could be attached directly to the tower legs and then
>feed the vertical section fed with a gamma match. That's not
>been tried here, but it's on my list of things to do for another
>vertical antenna.
>
>73,
>Charlie, N0TT
>
>
>
>------------------------------
>
>Message: 5
>Date: Wed, 16 Dec 2015 06:16:27 -0600
>From: Chuck Dietz <w5prchuck at gmail.com>
>To: Dave Thompson <thompson at mindspring.com>
>Cc: "towertalk at contesting.com" <towertalk at contesting.com>
>Subject: Re: [TowerTalk] Reverse Fed Towers
>Message-ID:
> <CAOk0j1-33W7hpvFxr+Vg5R56Sr7MKRA8m=r8DMKwUyz4N3aopQ at mail.gmail.com>
>Content-Type: text/plain; charset=UTF-8
>
>To avoid RF in the shack, bury the coax/hardline.
>
>Chuck W5PR
>
>On Wed, Dec 16, 2015 at 12:30 AM, Dave Thompson
><thompson at mindspring.com>
>wrote:
>
>>
>> Tom N4KG explained reverse feeding a tower in as I recall the May
>>1994
>> QST.
>>
>> Tom does a good job of making it easier and yes, this is an elevated
>> radial system. My main concern was not getting the radials far
>>enough off
>> the ground
>> to avoid ground loss. ON4UN told me the radials needed to be 40 feet
>>off
>> the ground to be safe. There was a report by Christman released at
>>Dayton
>> in the early 1980's where he built a half wave vertical dipole that
>> required isolators to be effective. K4PI looked at the design and
>>told me
>> it was too complicated.
>>
>> I built one using Spi-Ro short radials and using the MFJ 259 found
>>that my
>> 71 foot tower top loaded was matched at 1830 at 18 feet. A couple of
>> others used the design to make effective 160 or 80 meter verticals.
>>
>> Dave K4JRB
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
>
>------------------------------
>
>Subject: Digest Footer
>
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>------------------------------
>
>End of TowerTalk Digest, Vol 156, Issue 54
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