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Re: Topband: INV-L with traps

To: "'Alex'" <kr1st@amsat.org>, <topband@contesting.com>
Subject: Re: Topband: INV-L with traps
From: "Joe Subich, W4TV" <lists@subich.com>
Reply-to: lists@subich.com
Date: Sat, 26 Sep 2009 11:40:17 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
If you already have a wire inverted L, it's not that 
hard to convert to a trapped antenna using either the 
Reyco traps or home made coaxial traps.  See the info 
from K1ZM many years ago concerning the wire version 
of the BC Special: 
http://lists.contesting.com/_topband/1998-02/msg00057.html 

I'm including an edited version of the AA8U "Ugly-as-L 
Dxpedition Antenna" using Reyco (Unadilla) traps since I 
can't find the original e-mail in the archives.  Some have 
reported problems with trap failure when running high power. 
The Reyco traps seem to survive reasonable power levels but 
not "big"  amplifiers.

The Reyco/Unadilla available from many amateur shops seem 
to be the only off the shelf wire antenna traps covering 
all of the HF bands I can find these days.  

73, 

   ... Joe, W4TV 
 


> -----Original Message-----
> From: Bruce (AA8U)
> Subject: "Ugly-as-L" DXpedition Antenna
> 
> 
> I have been building an antenna to take on a DXpedition in 
> July to the South Cook Islands. I have received many requests 
> for dimensions and construction details since this design was 
> first mentioned on the reflector. 
> 
> This design evolved from a simple 160M inverted-L to its 
> present four-band form, as I realized we would likely have 
> some restrictions placed on the number of antennas we could 
> erect at the Rarotongan Resort Hotel. 
> 
> The first 160M version was a straight forward 234/f length 
> antenna with 60' vertical and the rest horizontal. It only 
> had 5 ground radials, each 133' spread out and laying on the 
> ground. It was fed with a 28:50 ohm Un-Un (W2FMI design).  As 
> I added traps to get additional bands, the overall length 
> decreased. I think the single band antenna would probably 
> perform slightly better than the final version. 
> 
> Bandwidth is adequate on the final version, but not generous, 
> except for the narrow 30M band. 
> 
> Ground losses for this design haven't been measured. 
> 
> The feed point resistances and SWR figures below were 
> obtained at the feed point using an MFJ-259 Antenna Analyzer. 
> A real nifty piece of test equipment!!! It has a calibration 
> error on the bands tested as indicated in the notes below. It 
> does give reliable indications when this factor is taken into 
> account.  
> 
> ==============================================================
>  Dimensions To Trap Centers      Fo         SWR    Feedpoint R
> --------------------------------------------------------------
> Feed point to KW-30 = 21' 4"   10.12 mHz.  1.10:1        50
> KW-30 to KW-40      =  7' 8"    7.05 mHz.  1.15:1        44
> KW-40 to KW-80CW    = 23'       3.61 mHz.  1.20:1        36
> KW-80 to insulator  = 39' 1"    1.83 mHz.  1.60:1        28
> 
> MFJ-259 resistance calibration: 50 ohms = approx. 42 ohms 
> actual @ 1.0:1 SWR.
> 
> Feed point 1' 6" above ground, mounted on short ground rod 2' 
> in earth.
> 
> Radials: 5 @ 133'
>          5 @  68'
>         10 @  33'
> 
> Wire use for the radiator and radials is #14 MTW (600 V 
> Insulation). Using bare copper wire for the radiator will be 
> require these dimensions to be increased by about 2%. 
> 
> ################################################################
> #   The "Ugly-as-L"  160/80/40/30M   DXpedition Inverted-L     #
> #   Antenna Designed and tested by AA8U                        #
> ################################################################
> # Tall                                                    Tall #
> # Tree      HI-Q Insulator      HI-Q Insulator            Tree # 
> # O---Dacron---====....39'1"........====------5/32"Dacron----O # 
> #                 [=] KW-80CW                                  # 
> #                  :                                           # 
> #                  :                                           # 
> #                  :                                           # 
> #                  :   23'                                     #

> #                  :                                           # 
> #                  :                                           # 
> #                  :                                           # 
> #                 [=]  KW-40                                   # 
> #                  :                                           # 
> #                  :    7' 8"                                  # 
> #                  :                                           # 
> #                 [=]  KW-30                                   # 
> #                  :                                           # 
> #                  :                                           # 
> #                  :   21' 4"                                  # 
> #                  :                                           # 
> #                  :                                           # 
> #                  X  feed point   (w/28:50 Un-Un on 160M)     # 
> #                  :    1' 6"                                  # 
> #   _____________radials__________________________________     # 
> #              (on ground)                                     #
> ################################################################


 


> -----Original Message-----
> From: topband-bounces@contesting.com 
> [mailto:topband-bounces@contesting.com] On Behalf Of Alex
> Sent: Saturday, September 26, 2009 9:33 AM
> To: 'cris blak'; topband@contesting.com
> Subject: Re: Topband: INV-L with traps
> 
> 
> Hi Cristi,
> 
> What a coincidence! I just finished building 80m and 40m 
> traps last night myself and was going to build the "Battle 
> Creek Special" this weekend. I have already an inverted L 
> (coaxial version), but supports in my small backyard are hard 
> to come by and always thought it was a waste to use the one 
> 60ft support I use for the inverted L for just one band (and 
> the radials!).
> 
> There are a lot of myths out there about traps being very 
> lossy (just like with anything else in hamradio). Some of 
> these myths are propagated by antenna manufactures who sell 
> antennas without traps. The loss incurred by traps is 
> actually not all that great. I found this article by W8JI very
> helpful:
> 
> http://www.w8ji.com/traps.htm
> 
> That pretty much convinced me to go ahead and build the 
> Battle Creek Special to get the best bang for my buck (and 
> who can't use that these days). The loss for coaxial traps 
> seems to be about 1.6 dB for TWO traps (he evaluates 
> dipoles). Of course some will cry tears over that kind of loss. 
> 
> The nice thing about the BCS antenna is that it will fit 
> using the same supports I have now for the coaxial inverted 
> L, which is only 125 feet in length.
>  
> I have no experience to share with you, but I thought it was 
> funny that you were thinking and doing the same thing at the 
> same time. :)
> 
> 73,
> --Alex KR1ST
> http://www.kr1st.com
> http://www.airlinkexpress.org
> 
> 
> > -----Original Message-----
> > From: topband-bounces@contesting.com [mailto:topband- 
> > bounces@contesting.com] On Behalf Of cris blak
> > Sent: Friday, September 25, 2009 5:09 PM
> > To: topband@contesting.com
> > Subject: Topband: INV-L with traps
> > 
> > Hello,
> > 
> > I have an INV-L for 160m which is working fine along with its 30 
> > radials. The vertical part is about 16m. I intend to add 
> two traps in 
> > order to use it on 80m and 40m. Is there anybody who use 
> such a design 
> > for DX (meaning "in practice"). What is the difference in terms of 
> > quality between an 160m INV-L and an 160m INV-L with trap or traps 
> > (80/40m)? I already build the traps for 80 and 40m with 
> RG58 coaxial 
> > cable and tune it with my miniVNA. The Q factor is around 20.
> > 
> > Thanks for any advice/ report.
> > 
> > 73 de YO3FFF
> > Cristi
> > 
> > 
> > 
> > _______________________________________________
> > Topband mailing list
> > Topband@contesting.com 
> > http://lists.contesting.com/mailman/listinfo/topband
> 
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