Topband: INV-L with traps
Joe Subich, W4TV
lists at subich.com
Sat Sep 26 08:40:17 PDT 2009
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 at contesting.com
> [mailto:topband-bounces at contesting.com] On Behalf Of Alex
> Sent: Saturday, September 26, 2009 9:33 AM
> To: 'cris blak'; topband at 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 at contesting.com [mailto:topband-
> > bounces at contesting.com] On Behalf Of cris blak
> > Sent: Friday, September 25, 2009 5:09 PM
> > To: topband at 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 at contesting.com
> > http://lists.contesting.com/mailman/listinfo/topband
>
> _______________________________________________
> Topband mailing list
> Topband at contesting.com
> http://lists.contesting.com/mailman/listinfo/topband
More information about the Topband
mailing list