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Re: [Amps] Asynchronous coax matching transformer

To: amps@contesting.com
Subject: Re: [Amps] Asynchronous coax matching transformer
From: Larry Benko <xxw0qe@comcast.net>
Date: Sat, 01 Aug 2009 19:34:55 -0600
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Roger,

You are confusing insertion loss with return loss.  A return loss of 
20dB is the same as an SWR of 1.22:1 which is also equal to a reflection 
coefficient of 0.1.  Insertion loss is a combination of dissipative 
(heat producing) loss and mismatched loss.

73,
Larry, W0QE

Roger wrote:
> Carl wrote:
>   
>> UHF connectors have varying effects but for all pratical purposes show a 
>> 20dB or better return loss thru 222 mHz before climbing. Many versions do 
>>   
>>     
> 20 db?  I've strung a whole series of connectors together and didn't get 
> half a db.  275 feet of coax (LMR 400) with connectors at the rig to 
> grounding panel/Polyphaser(2), cable to base of tower (2), bulkhead 
> connector, cable to top of tower (2),  grounded bulkhead connector, 
> pigtail to 2-way power divider(2), two cables from power divider to 
> antennas (2).  That's 12 connectors 15 if I count the so239s on the rig 
> and antennas.  The power reaching the antennas was only a few tenths of 
> a db less than that much cable without connectors.
>   
>> show RF heating due to poor quality insulation, even at HF.
>>
>> I refuse to buy imports and search out Amphenol, Kings, and other mil spec 
>> marked ones at hamfests, sometimes attached to a piece of junk coax.
>>
>>   
>>     
> I never use, used connectors or even reuse them except for the expensive 
> ones. Yes I do occasionally use imports, but I check the quality.  If I 
> get a batch that aren't up to par I pitch them rather than give them 
> away and have some one run into problems because they were trying to 
> save money.  That was one of the reasons I went to crimp connectors.
>
> 73
>
> Roger (K8RI)
>   
>> Carl
>> KM1H
>>
>>
>> ----- Original Message ----- 
>> From: "Joe Subich, W4TV" <lists@subich.com>
>> To: <TexasRF@aol.com>; <gm3sek@ifwtech.co.uk>; <amps@contesting.com>
>> Sent: Saturday, August 01, 2009 4:35 PM
>> Subject: Re: [Amps] Asynchronous coax matching transformer
>>
>>
>>   
>>     
>>>     
>>>       
>>>> If the sections are joined via coax connectors, you have to
>>>> take into account where 75 ohms ends and 50 ohms begins. The
>>>> connectors are invariably of a 50 ohm type and their internal
>>>> length must be added to the 50 ohm part of the matching section.
>>>>       
>>>>         
>>> It depends on the type of connector.  UHF connectors are often
>>> closer to 35 Ohms if I recall correctly.  N connectors can be
>>> either 50 or 75 Ohms ... if using a barrel for splicing, it is
>>> probably better to use a 75 Ohm barrel with a 75 Ohm center pin
>>> on the 50 Ohm cable (removing one stand of the center conductor
>>> if necessary).  If using a male/female connector pair then one
>>> would use 50 Ohm connectors and "build up" the center conductor
>>> of the 75 Ohm cable.
>>>
>>> For HF work - even through six meters - the connector length
>>> is less than 1 degree and can probably be ignored.
>>>
>>> 73,
>>>
>>>   ... Joe, W4TV
>>>
>>>
>>>
>>>
>>>
>>>     
>>>       
>>>> -----Original Message-----
>>>> From: amps-bounces@contesting.com
>>>> [mailto:amps-bounces@contesting.com] On Behalf Of TexasRF@aol.com
>>>> Sent: Saturday, August 01, 2009 1:38 PM
>>>> To: xxw0qe@comcast.net; gm3sek@ifwtech.co.uk
>>>> Cc: amps@contesting.com
>>>> Subject: Re: [Amps] Asynchronous coax matching transformer
>>>>
>>>>
>>>>
>>>> Hi all,in addition to the examples Larry offered, the scheme
>>>> will also
>>>> match impedances less than 50 ohms, down to 22.2 ohms if I
>>>> remember  correctly.
>>>>
>>>> A two way power divider where two 50 ohm loads are in
>>>> parallel requires a
>>>> 25 to 50 ohm transformer which is easily handled with the
>>>> series matching
>>>> method.
>>>>
>>>> The only down side is the difficulty in adjusting the
>>>> matching sections. On
>>>>  the other hand, transmission line calculations via Smith
>>>> Chart or computer
>>>>  program will give the exact lengths in degrees needed so
>>>> tuning is not a
>>>> real  requirement anyway.
>>>>
>>>> If the sections are joined via coax connectors, you have to
>>>> take into
>>>> account where 75 ohms ends and 50 ohms begins. The connectors
>>>> are invariably of
>>>> a 50 ohm type and their internal length must be added to the
>>>> 50 ohm part of
>>>> the  matching section.
>>>>
>>>> The last issue is velocity factor of the coax and connectors.
>>>> A serious
>>>> builder will be prepared to confirm these quantities before
>>>> cutting the
>>>> matching  sections to length.
>>>>
>>>> It is a real joy to go through the numbers and have the
>>>> transformer turn
>>>> out right on frequency.
>>>>
>>>> 73,
>>>> Gerald K5GW
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> In a message dated 8/1/2009 10:59:13 A.M. Central Daylight Time,
>>>> xxw0qe@comcast.net writes:
>>>>
>>>> Hi Ian  & Carl,
>>>>
>>>> Actually given only 50 ohm and 75 ohm coax and not
>>>> paralleling any coax
>>>> you can match all resistive impedances between 50 and  112.5
>>>> (75*75/50)
>>>> ohms.
>>>>
>>>> e.g.
>>>> 50 ohms ---- 29.3 deg. 75 ohm coax -----  29.3 deg 50 ohm
>>>> coax -----  75
>>>> ohms (as shown by the 1/12 wave  match)
>>>> 50 ohms ---- 40.5 deg. 75 ohm coax ----- 23.8 deg 50 ohm coax
>>>>  -----  85
>>>> ohms
>>>> 50 ohms ---- 58.3 deg. 75 ohm coax ----- 14.9 deg 50  ohm
>>>> coax ----- 100
>>>> ohms
>>>> 50 ohms ---- 90.0 deg. 75 ohm coax -----  0.0  deg 50 ohm coax ----- 
>>>> 112.5 ohms (std 1/4 wave match)
>>>>
>>>> Also many  reactive impedances are also easily matched
>>>> e.g.
>>>> 50 ohms ---- 42.6 deg.  75 ohm coax ----- 10.3 deg 50 ohm
>>>> coax ----- 75 -
>>>> j20 ohms
>>>>
>>>> For a  matching over a small range of frequencies
>>>> transmission lines work
>>>> well.
>>>>
>>>> 73,
>>>> Larry, W0QE
>>>>
>>>>
>>>> Ian White GM3SEK wrote:
>>>>       
>>>>         
>>>>>  Carl wrote:
>>>>>
>>>>>         
>>>>>           
>>>>>> Does anyone remember the formula  for matching 50 to 75
>>>>>>           
>>>>>>             
>>>> Ohms with 2
>>>>       
>>>>         
>>>>>> very short lengths of  coax? If I remember it used a 75
>>>>>>           
>>>>>>             
>>>> Ohm section
>>>>       
>>>>         
>>>>>> at the output of the  amp, and a
>>>>>>           
>>>>>>             
>>>> 50
>>>>       
>>>>         
>>>>>> Ohm section to the CATV hardline. Frequency  dependent of course.
>>>>>>
>>>>>> Its been about 25 years since I  built one.
>>>>>>
>>>>>>
>>>>>>           
>>>>>>             
>>>>>  http://www.tuc.nrao.edu/~demerson/twelfth/twelfth.htm
>>>>>
>>>>> By  paralleling two lengths of 50 or 75 ohm line, it can
>>>>>         
>>>>>           
>>>> also match to
>>>>       
>>>>         
>>>>> 25
>>>>>  or 37.5 ohms; or to even lower impedances by paralleling
>>>>>         
>>>>>           
>>>> three lengths
>>>>       
>>>>         
>>>>> of the same line.
>>>>>
>>>>>
>>>>>
>>>>>         
>>>>>           
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