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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