Hi Rick,
One more comment. I believe AM broadcast stations try to avoid phase
cancellation between skywave and ground wave, and therefore they try and
avoid antennas that have a high angle lobe. I'm pretty sure that's why the
AM broadcast stations that tried such things as a 5/8 wave length radiator
determined that this caused phase cancellation problems between ground wave
and skywave and abandoned radiators that were this tall. (I might have
some of the exact details incorrect, but believe I have listed the general
problem they ran into which caused them to rethink ground wave versus
skywave and their antenna designs).
Don (wd8dsb)
On Sun, Mar 1, 2020 at 9:22 PM Don Kirk <wd8dsb@gmail.com> wrote:
> Hi Rick,
>
> I use a 68 foot base loaded vertical on 160 meters, but I also use 3
> different pennant RX antennas. Unless it's ground wave, my 160 meter TX
> vertical is often deaf for stations in adjacent states that are in close to
> me (say 100 to 200 miles away). Sometimes I can barely hear these stations
> on my TX antenna, but when I switch to one of my pennant RX antennas they
> are booming in. What's also interesting during these period of time is
> that I can hear the stations pretty good regardless of what pennant I'm
> using (pennant pointed 40 degrees, pennant pointed 160 degrees or pennant
> pointed 270 degrees) even though my pennants have very good front to back
> ratio at low elevation angles (but not at very high elevations angles), and
> this is a good indication that NVIS is at play. The modeled elevation
> pattern of my TX vertical compared with my RX Pennants appears to explain
> this phenomena (certainly does not contradict it). Therefore during
> stateside contests it sure appears I could benefit by using an NVIS TX
> antenna for working these stations that are in close (adjacent states).
>
> I have never observed this phenomena when copying DX stations, or stations
> US stations far away.
>
> I posted the following information on my pennant website many years ago,
> and it still holds true based on massive amounts of time I spent on 160
> meters.
>
> --------------------------------------------------------------------------------------
>
> *Typical skywave signal to noise improvement on 160 meters using my
> pennants compared with my TX vertical*
>
> 0 to 1500 miles = 6 dB (and often much more for stations within 200 miles
> depending on NVIS)
> 2000 miles = 3 dB
> 4000 miles or more = 1 to 3 dB (Note : most often 2 dB, but sometimes
> only 1 dB) Revised Jan 25, 2016
>
> (The above numbers are just approximations based on many hours of
> comparison testing of my pennants versus my TX vertical antenna on 160
> meters.)
>
>
>
> ----------------------------------------------------------------------------------------------
> Just FYI, and 73,TX
> Don (wd8dsb)
>
> On Sun, Mar 1, 2020 at 8:38 PM Richard (Rick) Karlquist <
> richard@karlquist.com> wrote:
>
>> On 3/1/2020 5:26 PM, Mike Waters wrote:
>> > However, during stateside contests such as the ARRL 160, not having some
>> > NVIS would be a disadvantage.
>> >
>> > 73, Mike
>> > W0BTU
>> >
>>
>> How come AM broadcast stations don't need NVIS?
>>
>> Rick N6RK
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