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Re: Topband: Topband Digest, Vol 139, Issue 20

To: "Carl" <km1h@jeremy.mv.com>, "Mike Greenway" <K4PI@BELLSOUTH.NET>, <topband@contesting.com>
Subject: Re: Topband: Topband Digest, Vol 139, Issue 20
From: "Tom W8JI" <w8ji@w8ji.com>
Reply-to: Tom W8JI <w8ji@w8ji.com>
Date: Fri, 1 Aug 2014 11:06:21 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
Poor guessing by Carl.

The control units are entirely different. One is just a switch, and the other is a microprocessor based system that has an omni function and a hot switch lockout for relay protection. It also has a relay clean function.

I this the original poster was asking about Array Solutions vs. DXE, and not Comtek.

The original poster might have been asking about the phasing box???

The control head is in the house on the desk. The phasing box is out at the antenna. The various subparts of the system are very commonly called incorrect names, even by sales people. For example, the phasing box or outdoor unit is called a controller. The Q-sections that are nothing more than feedlines are called phasing lines. I never really am sure what part someone is asking about. :)

Another point about guessing...

The original error in hybrid 4 square design was from ignoring mutual coupling, and assuming element impedances were ~35 j0 for all four elements. The original thought was to transform the antennas to 100 ohms at the phasing box ports by using 1/4 wave 75-ohm Q sections. The 100 ohm ports were paralleled to get 50 ohms.

The problem with that idea is mutual coupling changes the antenna resonance and impedance. The antennas are not even close to the correct impedance, and are reactive with different signs when phased. The elements also require equal currents, not equal power. A hybrid tries to force equal power.

As far as I know, ****NONE**** of these units are true hybrids. This is because a true hybrid would have terrible F/B ratio and gain in this application. This is because:

1.) None of the elements or feedlines are 50 j0 when phased. They are all different impedances, except the center two elements. A hybrid ONLY provides the design phase when the termination is the design value, and that does not happen.

2.) None of the element groups require equal power. Equal power would result in a terrible F/B ratio.

The DXE outdoor unit, besides an omni function and sophisticated controller, is much better optimized for the impedances actually presented in the working system. Rather than accidentally working through a design shortfall in hybrid, like the original system many years ago was, it is planned for the loads presented by the system. Because none of these units are really hybrids (they would not work very well if they were), they are all different.

73 Tom



----- Original Message ----- From: "Carl" <km1h@jeremy.mv.com>
To: "Mike Greenway" <K4PI@BELLSOUTH.NET>; <topband@contesting.com>
Sent: Thursday, July 31, 2014 8:00 PM
Subject: Re: Topband: Topband Digest, Vol 139, Issue 20


More like a Chevy vs one thats been dolled up a bit for more money (-:


----- Original Message ----- From: "Mike Greenway" <K4PI@BELLSOUTH.NET>
To: <topband@contesting.com>
Sent: Thursday, July 31, 2014 2:25 PM
Subject: Re: Topband: Topband Digest, Vol 139, Issue 20


Hi Paul.. I have used two Comteks for over 20 years and they have never had a problem. The DXE looks like a very nice unit and it appears to me the circuitry is about the same.. Either should work well I think... Ford versus Chevy... 73 Mike K4PI

From: topband-request@contesting.com
Sent: Thursday, July 31, 2014 12:00 PM
To: topband@contesting.com
Subject: Topband Digest, Vol 139, Issue 20

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Today's Topics:

  1. 4-square controllers (Paul Baldock)


----------------------------------------------------------------------

Message: 1
Date: Wed, 30 Jul 2014 21:32:30 -0700
From: Paul Baldock <pbaldock@frontier.com>
To: <topband@contesting.com>
Subject: Topband: 4-square controllers
Message-ID: <20140731043244.B6490AC9F9A@mx.contesting.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

Does anybody have an opinion on the DX Engineering verses the Array
Solutions 4 square controller?

- Paul  KW7Y



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