Topband: Hi-Z 160M 200' 8 Circle

[Doug Turnbull]

Dear Friends,

 

        Last night was again an interesting time to listen to TB.    I am
now pretty sure that the 8 circle will under the right circumstances
delivers a 30 dB Front to Back Ratio.    The F/B can drop to about 22 dB as
well with 25 dB being most commonly observed.   It all depends on whether
the signals is strong enough to still be above the noise after this amount
of attenuation; what the noise floor itself is doing; beam heading and of
course the angle at which the signal is arriving.    I can tell you that the
beam pattern is amazingly sharp especially when you consider this is top
band.    I have seen up to 20 dB drop in a signal just by turning the
bearing 45 degrees.   Sometimes if I turn another 45 degrees the signal
remains the same, lowers or even goes back up two or three dB - this is to
be expected.   Imagine the help this is in a contest reducing QRM from
adjacent stations.

 

        Having said all of this, the eight circle can not change band
conditions.    I have yet to hear JA but no one close by is working them
either.   I did hear Greenland working a string of JA stations but both
countries were on the grey line at the time.    I tried to copy HL5IVL (call
?)for hours last night, but though I knew Kim was there and heard odd bits
from him he was too weak to call.   Yet some EU stations including LA were
working him with some stations reporting 59 on the cluster.    Now I have
worked Kim many times in the past even copying reasonably well on the
inverted L TX antenna.   Still this is frustrating but I suppose it is also
160M.

 

         Saturday night, I was copying JT5DX with a true 57 signal through
all the EU noise on SSB.   He was great copy with me and I had to do this
through a contest with splatter and many stations calling on his frequency
as this is CQWW.   So I copy JT on SSB but not HL on CW.   Top band makes
you work for it.    No doubt as the season progresses the JAs will be there
and I hope to work many.   When I had an 800 foot Beverage on JA there were
many winter evenings when I could not copy JA. 

 

         It is hard to fully evaluate the Hi-Z 200' 160M 8 circle but my
impression is that it is significantly (74 degree lobe vs 52 degree lobe)
more directive than the previous 160 and 80 meter 114' foot diameter 8
circle.   The pattern is sharper and deeper.    I do copy many signals with
this antenna which can not be copied with the TX antenna.   The noise level
drops from S4/5 to S0/1 when going from 160M inverted L (100' ft vertical
run) to the 160M only 8 circle.    Signals also drop but again I copy
signals even in the clear with the 8 circle which can not be heard with the
TX antenna.   I have seen comparisons between this 8 circle and a 5 element
Yagi - they are not the same type of antenna and this comparison is a bit
"hoaky" but I can see the essence of it.

 

          On Saturday night there was an unusual high level noise from the
south and boy was it handy to be listening in a more northerly direction as
then this noise just dropped out.   

 

           I think that sometimes too much attention is paid to the RDF
factor of the RX antenna and not enough to directivity. You can model RDF
but testing is another matter.  Yes RDF and directivity are related but they
are not the same.   In a contest or when trying to work a DX station
operating simplex; the directivity is a great help.    Of course as
mentioned above it is also a help when nulling noise from a given direction.

 

           I am still waiting for a local friend to run tests at different
times of the day for directivity with.    It would be helpful to get a
better idea of the front to back.

 

           Presently a 80/40 meter Hi-Z interlaced (two four squares rather
than all 8 elements active simultaneously) 8 circle with delay optimized for
40 meters is being assembled at 120 feet distance from the 160M 8 circle.
According to Lee KTJR, this is more than adequate separation for the two
antennas.   This antenna also works on TB so when completed there will be
yet another report.

 

           Unfortunately I went to the scratcher too early last night to
catch the 3C1.

 

                                                        73 Doug EI2CN