It just dawned on me that the reason why an inverted-L works so well for
many is because it radiates both vertically and horizontally.
Remember W8JI's experience where a nearby ham, using an inverted-L on a
small city lot in Toledo, Ohio did nearly as well as Tom with his 120'
tower with 120 full size radials?!
Barring unforeseen circumstances, the drone we just ordered will get here
in time to put a pulley for an inverted-L back up in the tree before the
Stew Perry.
73, Mike
www.w0btu.com
On Mon, Nov 26, 2018, 3:19 PM Mike Waters <mikewate@gmail.com> wrote:
> This has been an eye-opening discussion for me! I have always preached the
> 'gospel' of vertical-is-usually-best based on W8JI, ON4UN, and *many*
> other long-time Topbanders. Someday I'll have to revise
> www.w0btu.com/160_meters.html and include a link to this thread.
>
> I stand corrected. Thank you, gentlemen! :-)
>
> 73, Mike
> www.w0btu.com
>
> On Mon, Nov 26, 2018, 12:56 AM Steve Ireland <vk6vz@arach.net.au> wrote:
>
>> Hi Frank (and Rick)
>>
>> Somewhere I have a map of the lines of geomagnetic latitude superimposed
>> on a Mercator projection of the world, but I can’t find it right now.
>> Unlike the ruler-straight lines of conventional latitude, geomagnetic
>> latitude lines wander across the world like a collection of snake tracks.
>>
>> As a result of how geomagnetic latitude snakes across the globe, a
>> comparison can’t be directly made between similar geomagnetic latitudes in
>> the northern and southern hemispheres – where Tom W8JI lives is probably
>> very different to me in terms of the closeness of his geomagnetic latitude
>> to the electron gyro-frequency. As Carl K9LA points out, the geomagnetic
>> latitude relates to polarization and involves the ordinary and
>> extraordinary waves that propagate through the ionosphere, and how 160m is
>> affected by being close to the electron gyro-frequency.
>>
>> About 10 to 15 years ago, Carl, Nick Hall-Patch VE7DXR and Bob NM7M (SK)
>> (also a physicist like Carl, as I’m sure you recall) helped Mike VK6HD (SK)
>> and I to understand why our horizontal cloud-warmers outperformed efficient
>> vertical antenna systems in SW WA.
>>
>> You are quite correct, the Fresnel zone where I live (the mostly far
>> field region where ground gain is developed) has very poor conductivity.
>> And, to repeat your point as this is not as widely known as it should be,
>> poor Fresnel Zone conductivity has very little impact on the performance of
>> horizontally polarized antennas, while having a major impact on vertically
>> polarised ones.
>>
>> While the Fresnel (far field) zone of my location, is basically rock
>> (granite and ‘coffee rock’), Mike’s final location beside the Kalgan
>> estuary appeared to have much better Fresnel zone conductivity, with less
>> rock than me and, in around half the compass directions, salt water.
>> However, his inverted-L with an 80’ vertical section over 120 buried
>> quarter-wave radials at Kalgan performed only marginally better than our
>> previous attempts at vertical antenna systems did.
>>
>> On this basis, I came to the conclusion that the dominant problem was
>> likely to be the geomagnetic latitude issue, rather than poor conductivity
>> in the Fresnel zone – which it certainly is also an issue here.
>>
>> To investigate this further, I sought out the opportunity to operate
>> directly by the sea here with a good vertical antenna. After much
>> paperwork, I managed to get permission to operation from the Cape Leeuwin
>> lighthouse, which is 40m-plus high and on a narrow finger of land
>> surrounded by sea for over 300 degrees.
>>
>> In a Stew Perry TBDC in the early 2000s, with the assistance of my friend
>> Phil VK6PH, we put up a full-sized quarter-wave wire vertical on the most
>> seaward side of the lighthouse, less than 60 metres from the sea. This was
>> fed against a quarter wave counterpoise and the feeder decoupled with a
>> large ferrite choke to stop common mode effects. On the other side of the
>> lighthouse was an inverted vee half-wave dipole. Both antennas were
>> supported from the lighthouse balcony (at about 40m!) and detuned when not
>> in use. An Yaesu FT-1000MP was used, running less than 100W
>>
>> Unfortunately conditions were poor during our evening time into North
>> America, but at about three hours before sunrise the 160m band opened into
>> Europe. Right from this point, the vertical was slightly down on the
>> inverted vee by a few dB, but I would always call on the vertical first and
>> then switch onto the inverted vee if I got no response. All the way until
>> just after sunrise, the inverted vee outperformed the vertical, mostly
>> raising the stations who did not hear us on the vertical.
>>
>> The only time this situation was reversed was when 160m started to go out
>> as the sun started to rise and I had by then switched over to just calling
>> stations on the inverted vee.
>>
>> After about five minutes of this, the Europeans I could still hear were
>> not coming back to me anymore. Out of curiosity, I switched to the
>> vertical – and found I could still raise a few of them. I recall vividly
>> the last QSO with a CT1 using the vertical about 20 minutes after sunrise,
>> exchanging 559 reports.
>>
>> The crazy thing is that the vertical appeared to be doing exactly what a
>> dipole is known for doing on 160m in the northern hemisphere in some cases
>> – extending the sunrise opening. However, this was the only time the
>> vertical outperformed the inverted vee.
>>
>> As far as I know, Mike VK6HD never experienced this phenomenon when he
>> was comparing his inverted-L quarter wave antenna against his inverted vee
>> dipole. However, my vertical antenna was directly adjacent to the sea,
>> surrounded by sea, which may have helped.
>>
>> The final event was highly interesting, but did not sway me into
>> repeating the experiment the following year when I also operated from the
>> lighthouse in the Stew Perry TBDC.
>>
>> The fact was the inverted vee had been responsible for 80 to 90 per cent
>> of my QSOs - can’t remember exactly how many – while the vertical had only
>> accounted for three or four.
>>
>> Mike VK6HD, Phil VK6GX and I are not the only ones to have experienced
>> the “verticals aren’t always best for DX” situation here. About five to ten
>> years ago, I understand a group of German DXers came here and operated in
>> the CQ WW CW (I think).
>>
>> The group operated from the the Northern Corridor superstation
>> VK6ANC/VK6NC, using a quarter wave vertical on 160m. After disappointing
>> results, one of the ops (Mar DL3DXX, I think) recalled Mike, Phil and I
>> used inverted vees at 90 to 110’ and suspended a inverted vee dipole as
>> high as they could and changed over to using this. My understanding is then
>> they found they could work a much larger amount of DX stations on 160m.
>> ...
>
>
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
|