[Hi-zreceivingarraydiscussions] DIRECTIVITIY 8 CIRCLE

Sat Nov 30 20:34:47 EST 2013

I just ran some theoretical plots of the array at 1.84 MHZ. The 200 foot dia
8 element array shows 44 dB of F/B. Of course it is unlikely we would ever
see that much. However I routinely see 30+ dB in practice. I scaled all
phases on an 8 element 200 foot dia array  to 1MHz in the BCB and sure
enough as I remembered there is little if any low angle pattern. It is
almost circular with less than 10dB of F/B. This 8 element array was
designed to only work from 1.8 to 2 MHz. Or 3.5 to 4 MHZ when scaled to 100
foot dia and new delay cables.
  Interestingly enough I have tried the Broadcast F/B determination many
times. What I have discovered is that not all BCB stations seem to have that
ground wave low angle and do not always show F/B on the arrays. No, I have
not tried to figure out why. Maybe it's a mix of high angle skywave and
ground wave. What I do know for a fact is that early morning signals
sometimes come in at high angles and show little directivity for a period
during sunrise.
  A classic example of that was FT5XO that came in solid on arrays and
beverages until late in the sunrise and then switched to no directivity and
best reception on my TX vertical.
  We have had some recent reports from Alaska where there is no soil only
rock dust from glaciers. The reports showed that at low frequencies like 160
a Hi-Z array needed some extra ground help. Adding some short radials has
helped the situation but I remember back to my original research where I
found radials to be pretty sensitive to placement. I also at times have
suggested shallow burying of a plate of metal to increase the surface area
of the element ground to the earth. My early research indicated this to be a
bit more stable than hoping to place radials accurately. Accuracy is why
these arrays are able to do what they do.
Lee   K7TJR

-----Original Message-----
From: Hi-zreceivingarraydiscussions
[mailto:hi-zreceivingarraydiscussions-bounces at hizantennas.com] On Behalf Of
Dave Anderson, K4SV
Sent: Saturday, November 30, 2013 4:18 PM
To: Hi-Z Receiving Array Discussions
Subject: Re: [Hi-zreceivingarraydiscussions] DIRECTIVITIY 8 CIRCLE

Hi Everyone,

I have had my 200' 8 circle for nearly 2 years now.  In my case I have
installed my 4 square inside of the 8 circle.  This allows me to have both
controllers in the same cabinet. 

For 160 meters,
The 4 square works very well with great F/B.  My 8 circle works well but
depending on the arrival angle of the signals the F/B varies.  I do not
think the 8 circle has ever has 30+ DB of F/B.  I am using a ~3 foot 5/8"
ground rod (8 foot rod cut into three pieces) for each antenna.  My array is
out all by itself away from any metal objects on a small hill.

Lee's comment about it should have a 30+ DB F/B is interesting.  If
grounding is the key I will go out tomorrow and add more ground rods/radials
and give it a try to see if it will indeed improve F/B.  Comments?

My 8 circle works not bad on 80 meters either, directional too.

When I test my 8 circle/4 square and other receive antennas for F/B I try to
do this during the middle of the day using ground wave from an AM broadcast
station 100 miles away or so.  This was suggested by Jose N4IS when testing
the Waller Flag I built.  When using an application called Polar plot and
testing the WF I can easily see the pattern of the WF.  This might be a
trick that can be used to check F/B on other receive antennas. 

I have attached a plot of the 8 circle when using Polar Plot.  Once I
started Polar Plot I switched the 8 circle through its range.  You can read
the F/B from an AM station some 80 miles away.

Comments?

Dave Anderson, K4SV
Tryon, NC
 828 777-5088

www.K4SV.net

On Saturday, November 30, 2013 6:54 PM, kd9sv <kd9sv at comcast.net> wrote:

Lee, 30db F/B is about what I am seeing on my 4sq with 80ft/side which is
>located about 400ft in the clear in an open field...de gary
>
>-----Original Message-----
>From: Hi-zreceivingarraydiscussions
>[mailto:hi-zreceivingarraydiscussions-bounces at hizantennas.com] On 
>Behalf Of Lee K7TJR
>Sent: Saturday, November 30, 2013 5:56 PM
>To: 'Hi-Z Receiving Array Discussions'
>Subject: Re: [Hi-zreceivingarraydiscussions] DIRECTIVITIY 8 CIRCLE
>
>This will be an interesting thread. The Hi-Z 8A was only designed to 
>work on a single band, but to produce the best SNR currently available on
that band.
>I suspect your observations are what I would expect on other bands. If 
>operating on multiple bands, I would suggest changing over to a 4-8Pro 
>which is a 3 band array and shows reasonable directivity on all three. 
>With of course, slightly less available SNR of received signals than 
>the single band array.
>   All that being said, I have heard that the 8A actually hears 
>reasonably well on 80 Meters while not showing much directivity.
>I personally have not seen the need for common mode protection however 
>every install is usually different. If you are seeing 30+ dB of front 
>to back ratio on 160 meters I suspect your ground rods are quite adequate.
>
>What say others?
>
>Lee  K7TJR
>
>-----Original Message-----
>From: Hi-zreceivingarraydiscussions
>[mailto:hi-zreceivingarraydiscussions-bounces at hizantennas.com] On 
>Behalf Of k4pi at bellsouth.net
>Sent: Saturday, November 30, 2013 2:13 PM
>To: hi-zreceivingarraydiscussions at hizantennas.com
>Subject: [Hi-zreceivingarraydiscussions] DIRECTIVITIY 8 CIRCLE
>
>I have an 8 circle in 200 ft diameter.  I notice the F/B and F/S are 
>mainly only good on 160.  Even on the upper portion of the BC band for 
>the most part the F/B is not great.  Not that I need this but I have 
>used Hi Z 4 squares with 90 ft on a side and they seem to have good F/B 
>on the BC band and other bands.  On 80 with the 8 circle I can tell the 
>most predominant direction of a station but there is little F/B and 
>F/S.  Just wondering if this is what others are seeing.  It receives fine.
>
>I am well pleased with the system but just wondered what others were
seeing.
>I am using only a single 4 ft ground rod and wondered if anyone else 
>had seen any improvement of the system with more ground rods.  Also 
>wondered if anyone else was using common mode chokes in the feed line 
>as recommended by ON4UN's Low Band DXing book.  I have one at the 
>receiver end built from K9YC data.  My feedline is about 450 ft long 
>being cable TV hardline.  It is grounded once in the middle.
>
>Would like to hear from others on their experience.
>
>73 Mike K4PI
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