[TowerTalk] 4 square for 80

Fri Sep 23 15:59:10 EDT 2016

I disagree with this advice, Tim. Such a choke is strongly inductive 
below about 30 MHz, so its common mode Z will be cancelled, at least in 
part, by the capacitance of a feedline shorter than a quarter wave.  A 
multiturn choke wound on one or more #31 cores is predominantly 
resistive, so performance is far less affected by the impedance of the 
common mode circuit.

73, Jim K9YC

On Fri,9/23/2016 12:36 PM, Tim Duffy wrote:
> Hello Jeff,
>
> I like using the W0IYH style of choke in this application. It has several K
> ohms of CMI and goes right in series with the RG-11 line. In a 4 square the
> W0IYH choke must use 75 ohm coax and it also becomes part of the phasing
> line calculation for the 90 degree lines (typically cut for 3.650 MHz).
>
> You can see it here:
> https://www.dxengineering.com/parts/com-cfc-75
>
> 73,
> Tim K3LR
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Jeff
> AC0C
> Sent: Friday, September 23, 2016 3:25 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] 4 square for 80
>
> Tim, you mention below that the elevated radials and the control box must be
>
> choked.
>
> What's the general advice on the choke for each end of the line?
>
> 73/jeff/ac0c
> www.ac0c.com
> alpha-charlie-zero-charlie
>
> -----Original Message-----
> From: Tim Duffy
> Sent: Thursday, September 22, 2016 4:12 PM
> To: cqtestk4xs at aol.com ; towertalk at contesting.com
> Subject: Re: [TowerTalk] 4 square for 80
>
> Hello Bill,
>
> I want to clarify some of your notes below, as many guys are reading your
> post and might be confused. We need to insure we get this right.
>
> T top elements (loaded) will not have a feedpoint impedance of 36 ohms +/-
> j0. The hybrid coupler four square boxes are predicated on FULL size 1/4
> wavelength elements - so DXE does not recommend using loaded elements. The
> system will not work properly.
>
> I listened to your call with Rod, K8AAV here at DXE to make sure we have
> this right. Rod said that you SHOULD NOT use raised radials as they are hard
> to get working correctly. They MUST be tuned to work and there is a process
> for this. You also need to install chokes when using elevated RG-11 feed
> lines at the element feedpoints and at the Comtek box; otherwise there is
> significant pattern distortion. They can work - but it takes lots of
> patience and we recommend traditional ground mounted radial systems for best
> performance.
>
> The tower in the middle of your 4 square will interact with your proposed
> system. How much or how little depends on many factors. Rod reviewed the
> detuning approach with you - which is almost impossible for you to install
> with a rotating tower.
>
> Having engineered 4 square antenna systems (successfully) for over 25 years
> - I was the advising engineer to Rod on your project. I was very careful to
> make sure Rod had all of his facts correct before giving you advice.
>
> You asked for advice on your project and we gave you the straight engineered
> scoop - with tons of experience. We do not want you to go through lots of
> work only to find out a system you proposed does not work correctly. You
> might get various other guidance from others, my advice is be careful.
>
> Trying to make everything work properly on one tower like this is very hard
> and there is no free lunch. Only properly engineered systems have a high
> probability of working correctly.
>
> Please feel free to call or email me directly to discuss your options.
>
> Very 73,
> Tim K3LR
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Bill
> via TowerTalk
> Sent: Thursday, September 22, 2016 4:00 PM
> To: TOWERTALK at contesting.com
> Subject: [TowerTalk] 4 square for 80
>
>
> This will be my first foray into the world of 4 square xmit antennas.
>
> Plans are to make the elements from wire, suspended from the tower by rope
> at about 80 feet.  Due to the slope of the ropes from the tower to the
> ground, the elements might wind up a little short.  Plans were to T-top them
> running the wire parallel to the rope.  The elements might be around 60 feet
> so it would not be that hard to T top them to make up the extra length
> needed for 1/4 wave.
>
> I had planned to do the following:  Have an elevated ground system a 1/4
> wave radials running from the base of each vertical.  Height of the system
> would be 10 feet.  Radial system would consist of 16 radials for each
> vertical using the Comtek 4 square system to control it.
>
> In talking with the guys at DX Engineering about the planned setup I was
> given the not so good news.
>
> First, I was told you CAN NOT use an elevated ground system with the 4
> square.
>
> Second, I was told the tower would interfere with the system.  They said I
> would have to cage the tower to make it "invisible" to the system.  Caging
> the tower is impossible since it is a rotating tower and the cage would wrap
> on the stacks mounted on the tower.
>
> Was he right about all of this?
>
> I can not put up another tower due to tower restrictions (one tower
> allowed), so the only way I can get enough height to suspend the wires is to
> use the tower I have.  The county thinks anything 60 feet high constitutes
> another tower, so I can't make aluminum verticals.  No trees around either
> for supports.
>
> I really am in a bind for 80 if all this is true.  An inverted Vee  at 80
> feet is far inferior to the 4 square I had planned.
>
> Ideas and thoughts on this?
>
> Bill K4XS/KH7XS
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