Note: the following is not a theoretical or untested antenna. There
are working antennas in the field using the folded counterpoise
described below, scoring well in contests**, in use up to a year and
more. Contest scores of the sort attained are not made using antennas
with significant deficiencies or fundamental flaws.
A miscellaneous end-fed inverted L or end-fed inverted U over an
elevated 5/16 wave single wire folded counterpoise (FCP) will have
good radiation from a small lot, with the ability to put out a strong
signal not usually associated with small lots. In the simple
implementation of this antenna (160 only), the length of the L or U is
adjusted for zero reactance, usually resulting in a 50-60 ohm feed Z
at resonance.
There are NO radials. The main design point of the antenna is to
minimize lossy currents induced in the dirt and confine TX signal
current to the FCP and the radiating wire. This is a real, and lossy
issue for a few short or miscellaneous radials. Enough of an issue to
kill 15 dB.
The radiating wire first goes up as much vertical as you can manage,
then out as far as manageable, and then down if length is still needed
to prune to resonance. The main point is to pick a feed point on the
property that has your best vertical rise and then get the rest of the
length for resonance however you can. For some properties this has
meant putting extra angles in the up+over+down radiator. Some
properties will not need the "down" part.
The antenna uses a REQUIRED isolation transformer at the feed point
because the counterpoise is NOT resonant, and the feed would really
rather use the much lower Z but hugely lossy coax shield current as a
counterpoise. The folds in the FCP are designed to maximally reduce
counterpoise fields at the ground, reducing lossy currents in the
dirt.
The isolation transformer's leftover inductive reactance, a
disadvantage in many applications, in this case helps to tune out the
capacitive reactance of the FCP and reduces the length of the
radiating wire needed to achieve simple resonance for the antenna.
The counterpoise extends plus and minus 33 feet from the feed point,
167 feet folded into 66 linear feet occupied on the property. The
middle 20 feet of the 66 should be straight, but either end can be
bent away from the straight line to accommodate the property. Up 8
feet or higher is recommended. Lowering the counterpoise increases
the coupling to dirt, increasing losses.
The isolation transformer uses the same physical components as a
balun, but the unlike the balun there is NO connection of any kind
between the primary and secondary windings. This is accomplished with
twenty bifilar turns of double polyimide insulated #14 with teflon
sleeving wound on an Amidon T300A-2 #2 material powdered iron toroid.
One wire is the primary, and the other is the secondary. The low MU
powdered iron toroid was picked over time to avoid heating, still
provide required coupling, with other choices sometimes failing in
spectacular fashion. We have no information of our currently-used
winding method on the Amidon T300A-2 ever failing for any cause,
though we would not expect it to survive a direct lightning strike.
With the isolation transformer, the antenna and FCP is entirely above
ground and not connected to anything else. We use a 5 megohm resistor,
in parallel with a non-resistor lawn mower spark plug, from the FCP to
ground as a static drain. The gap drains lightning induced voltage to
protect the resistor, the resistor drains wind, snow, rain static.
The resistor and gap protect the winding from a voltage puncture that
will grow into a carbon track to ground.
73, Guy.
** As reported in Dec 2011 CQ, Jan 2011 CW160CW contest, USA low
power unassisted, the 29 scores over 100K out of 335 scored logs in
class:
Station, state, score, QSO, ST+PROV, DX
K9AY WI 259,346 991 58 36
W0UO TX 250,716 882 58 44
K1EP MA 232,750 909 56 39
K2AV NC 223,908 907 57 37 << No radials, 5/16 FCP
K8BL OH 203,328 819 58 38
KU1CW KS 197,885 795 58 37
N2WN TN 191,090 640 55 42
WB8JUI OH 190,372 852 58 38
N7IR AZ 183,855 856 58 27
W2TZ NY 178,633 723 56 35
NA8V MI 177,030 793 59 31
W4AA FL 173,619 494 56 45
K1HTV VA 172,956 733 55 32
W1WBB RI 161,550 654 55 35
KU8E GA 152,613 615 58 35
W7RH AZ 135,369 500 55 34
K4WI AL 128,520 509 55 30
N9NCK WI 126,162 516 55 31
KV8Q OH 125,741 674 57 20
N9AUG OH 125,330 608 55 28
W2TX FL 121,800 504 52 35
K9QVB IL 120,120 641 56 21
WW3S PA 119,848 706 55 16
K2UF NY 119,392 541 53 29
K0PK MN 118,400 678 58 16
WF4U UT 114,239 664 56 15
W1BYH MA 106,444 404 54 35
W5WMU LA 106,020 574 54 22
N4JF AL 101,920 493 54 26
** 3830 claimed scores listing of Dec 2011 ARRL 160 contest, North
America low power unassisted, top 20 of 119 listed as of this writing:
Station, state, score, QSO, ST/PROV, DX
2011 ARRL 160 - 3830 Claimed Scores 06Dec2011
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Call QSOs Sec Cntry hr Score Club
NA Single Op LP
K8FH 920 74 18 27 175,076 Medina 2 Meter Group
NE9U 978 75 14 172,927 MWA
K4FT 976 75 9 28 166,236 KCG
WB8JUI 940 71 9 21.32 152,560
K0TI 920 76 5 21 150,255 MWA
K0DI 875 75 8 28 146,495 Lincoln ARC
K2AV 788 65 9 21.5 119,066 PVRC << No
radials, 5/16 FCP
W0DLE 725 74 3 21 112,343 Grand Mesa
K9MMS 653 74 10 16 112,224 SMC
K0PK 657 72 6 19 104,130 MWA
K3PA 618 74 7 101,817 Kansas City DX Club
WA1FCN 645 68 7 99,864 ACG
K2ZR 695 64 4 20.0 90,112 Western NY DX Associ
K0AD 584 75 6 10 88,500 MWA
W0UO 519 71 9 14 85,680 NTCC
K0CN 478 73 11 83,076 MWA
N1IX 516 60 10 13 78,540 YCCC
VE3OSZ 442 68 15 77,854 CCO
W9ZRX 492 69 8 20.5 77,616 SMC
W7RH 437 72 8 76,869 Arizona Outlaws Cont
On Sun, Dec 4, 2011 at 8:18 PM, Jim Miller Waco Texas WB5OXQ
<wb5oxq_1@grandecom.net> wrote:
> With limited space what is the best antenna for 160? The only room available
> is a 130X50' area. Ground radials will be nearly impossable to put in large
> enough to be of much value. 1/4 wave antenna tried, very narrowband and
> interfeared with every receiving device in a block. I may just be out of
> luck. wb5oxq
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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