[Elecraft] SWR Readings:Differences

Wed Sep 3 13:38:06 EDT 2014

Add to the list.
The PL-259 has an undersized center pin.  I've seen these.

73 de Brian/K3KO

On 9/3/2014 14:20, Mel Farrer via Elecraft wrote:
> Good list, and here at least is one more.
>
>
> # PL-259 male or female connector made of some non-solderable material.  Looks like it soldered but isn't. Cheap import.
>
> Mel, K6KBE
>
>
>
>
>
> On Wednesday, September 3, 2014 6:57 AM, Guy Olinger K2AV <k2av.guy at gmail.com> wrote:
>
>
>
> Here is a small, non-inclusive list of things that can be bad with a coax
> run to the house. I have personally seen all of them at some time or place.
> Some big names, too.
>
> 1) At either or both ends, the shield was not soldered to the PL259 shell,
> and the connection has dwindled to a small percentage of the shield due to
> gradual destruction of the fine wire touching points.
>
> 1a) Ditto for the center conductor to the hollow center conductor pin of
> the PL259. Amazing how many PL259's are not soldered in a hurry to 'hear
> how it works". I've done it myself and forgotten I didn't. For years.
>
> 2) "Balun" is cheep junk, or burned up/melted/shorted
> turns/cracked/destroyed core, now junk.
>
> 3) Coax on tower is not high quality, and does not have it's weight
> supported. The stretch has changed the separation of shield and center
> conductor, and the characteristic impedance has shifted, introducing an
> unwanted transformation into the equation.
>
> 3a) Coax is very old, but still "looks OK" even though it isn't. Much coax
> material undergoes very slow (even decades) chemical changes which can
> change characteristics. Wide frequency and TDR scans of coax into opens,
> shorts, checked 50 ohm and 200 ohm terminations are only way to check for
> still-OK-ness.
>
> 4) Water has invaded the coax, from a nick, tear or critter bite in the
> jacket, or non/poorly sealed coax connector, and capillary action has
> wicked along it's entire length. This can be hundreds of feet in the worst
> of cases. The loss-added coax does not necessarily stay at 50 ohms Z zero.
> I have seen coax shields green (copper oxide) their entire length.
> Interestingly the practical outcomes of this extra loss was initially most
> often blamed on the transceiver.
>
> 5) Coax has been wrapped around a pipe by rotator torque. See 3)
>
> 6) Coax has had something heavy dropped on it. See 3)
>
> 7) Coax shield was only ground path for induced current for a close
> lightning strike. (Usually a direct strike smokes coax beyond any
> confusion.)
>
> 8) PL259 shell was not pliers-tightened and has worked loose, gradually
> producing burned points of connection.
>
> 9) Long coax run was laid tight in summer heat, and stretched in the
> winter. See 3)
>
> 10) Constant flexing of coax finally breaks the center conductor. After
> that, "connection" is strange.
>
> 11) Unsupported aerial coax over-weighted by ice and stretched, pulled out
> of connectors, see 8).
>
> 12) Coax is innocent and it's really the antenna.
>
> 13) Operator in fact does not know how to operate the instrument or how to
> interpret readings.
>
> 14) Short lengths of coax and "other boxes" are ignored, and those in fact
> contain the problem.
>
> 15) Measuring instrument has been damaged or was defective from the
> factory.
>
> 15a) Measuring instrument is cheep junk.
>
> 16) Operator was "told" what the trouble was by a "trusted source" and is
> having a lot of trouble thinking outside of the "trusted box" when the
> trusted source was in fact in error for this instance.
>
> 17) Dummy load used to calibrate/provide 50 J zero comparison or reference
> termination is not 50 J zero for any number of reasons, including the likes
> of several seconds of QRO on a 2 watts worth of 50 ohms. Didn't turn black
> on the outside, but the resistor innards were already toast. Didn't *look*
> burned, so must be fine, right?
>
> 18) Dummy load while accurate at DC has significant reactive components at
> RF.
>
> 19) Coax was not 50 ohms from the get-go (try 56). But it looks good so it
> must be good. And the seller had a nice looking web page and the best price.
>
> 20) I need to wrap this up, but I know I'm not remembering something really
> juicy, which will come to mind after I hit the send button.
>
> A group of Olde Pharte hams sitting around a table in a Lunche Jointe, came
> up with a napkin version of this that had over 40 items on it. The napkins
> were used for the inevitable outcome of ribs, and so was lost to posterity.
> One of these included a male F connector that had not had its threads
> grooved into the shell. This ignominious occurrence is not mentioned above,
> because it could not ever be part of a "working" setup. But it was amazing
> how many other things were blamed for "not fitting", including calls to an
> equipment maker about female chassis connectors, before the lack of threads
> was noticed.
>
> Good luck to all and 73,
>
> Guy K2AV
>
>
>
>
> On Wed, Sep 3, 2014 at 12:18 AM, Vic, K2VCO <k2vco.vic at gmail.com> wrote:
>
>> If your line is lossless (it isn't) you would expect the same SWR
>> readings anywhere along the line. With practical lines that have some
>> loss, the SWR should be LOWER farther away from the antenna. You are
>> getting the opposite result.
>>
>> One cause of erroneous SWR readings is RF flowing on the outside of the
>> coax. If your rotary dipole doesn't have a balun, this could be the cause.
>>
>> It's also possible that you have a bad connector or bad piece of coax
>> between the tower and the K3.
>>
>>
>> On 9/3/14 3:06 AM, pastormg2 at verizon.net wrote:
>>
>>> Good Evening, This is Mark Griffin, KB3Z and I have some questions
>>> regarding the SWR readings I get at my tower versus what I get on my
>>> K3. I will give the SWR readings that I got at my tower for a 40
>>> meter rotatable dipole at 55 feet.
>>>
>>> Tower:
>>>
>>> 7000  2.2 7025  1.8 7050  1.5 7075  1.3 7100  1.0 7125  1.1 7150
>>> 1.3 7175  1.6 7200  2.0 7225  2.2
>>>
>>> K3 Readings:
>>>
>>> 7000  3.5
>>>
>>> 7025  3.2
>>>
>>> 7050  2.9
>>>
>>> 7075  2.6
>>>
>>> 7100  2.4
>>>
>>> 7125  2.3
>>>
>>> 7150  2.4
>>>
>>> 7175  2.5
>>>
>>> 7200  2.6 7225  2.9
>>>
>>> What would cause such a big difference. The cable run from my antenna
>>> switch on the tower to my K3 is only an additional 75 feet. I am
>>> using RG-213 cable. Is there anyway that I can test the SWR reading
>>> that my K3 is giving me?
>>>
>>> Mark Griffin, KB3Z
>>>
>>
>> --
>> Vic, K2VCO/4X6GP
>> Rehovot, Israel
>> http://www.qsl.net/k2vco/
>>
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