Arent network analyzers wonderful tools Larry?
I too was confused by the competing arguments long before the Internet got
up to speed and let a VNA talk to me.
My "varying effects" comment was due to the same results that you noted but
for ham use it wasnt enough for me to worry about. Its similar to checking a
bunch of relays for isolation and not bothering to worry about a dB or 2
difference down in the -70 -80 dB region.
Carl
KM1H
----- Original Message -----
From: "Larry Benko" <xxw0qe@comcast.net>
To: "Carl" <km1h@jeremy.mv.com>
Cc: <lists@subich.com>; <TexasRF@aol.com>; <gm3sek@ifwtech.co.uk>;
<amps@contesting.com>
Sent: Saturday, August 01, 2009 8:59 PM
Subject: Re: [Amps] Asynchronous coax matching transformer
> Carl,
>
> I asked myself what a mated PL-259/SO-239 connector "really" looked like
> RF wise many times after hearing all kinds of horror stories. Finally
> after procuring a couple network analyzers and the understanding of how to
> make the measurements I decided to make a bunch of measurements with many
> different connectors. Just about every measurement produced slightly
> different results but after averaging them I came to the conclusion that a
> mated UHF M-F connection was a piece of 30 ohm transmission line that was
> 4.2 electrical degrees long at 100 MHz. Using those numbers would equate
> to a 222 MHz return loss of 21.2dB (1:19:1 SWR) which is pretty close to
> your experience.
>
> 73,
> Larry, W0QE
>
> 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
>> 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.
>>
>> 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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