[K3CAL] Spool of hardline in Noell garage
Shawn Donley
n3ae at comcast.net
Fri Oct 19 18:33:54 EDT 2018
Hi Tom,
Well, the unknown is the length of the hardline. I know (by measurement) it was 250 ft (physical length) when we brought it to the tower. What I don't know is if the installers cut some off at the top.
The TDR measurements suggest an impedance discontinuity at 230 ft (physical length accounting for velocity factor). That discontinuity could just be the mismatched antenna if the hardline was trimmed to 230 ft during installation. Or it could be a defective hardline at the 230 ft point due to mechanical damage if the original 250ft length was used.
To add another variable, the TRD measurements made using a Rig Expert exhibited some anomalies that the company has yet to explain to me. Your email prompted me to poke them again for answers. The Rig Expert uses frequency domain measurements and inverse Fourier transforms on that data to recover the impulse and step time domain responses rather than a traditional pure time-domain reflectometry measurement. There are nuances that can trip up such a method. Anyone who wants to get a good headache can read about it at http://literature.cdn.keysight.com/litweb/pdf/5989-5723EN.pdf
Shawn
> On October 19, 2018 at 1:50 PM kb2bcg at arrl.net wrote:
>
> Greeting from out west. We have already had our first snow and it is getting cold, but it is beautiful. Liz and I settling in (I forgot how much fun setting up a new house can be, but it is coming together nicely.) Not much in the way of ham radio yet (An antenna for 2m/70 cm and a long wire aimed north to south is a far as I have gotten, but it is a work in progress.)
>
> Concerning the hardline, I would think it should be possible to figure out if the bump in the line is a fault or the antenna. (Shawn, I am expecting that you will point out where my thinking is flawed. Thanks) Here is my thinking;
>
> 1. We know where the fault is (as determined by the TDR readings)
> 2. We know where the antenna is on the tower (just look up)
> 3. If the two number match, then it is the antenna. If they don't, then it is something else.
>
> Additionally, depending on the fault in the line, there may be more than one reflection. (one from the fault and one from the antenna.)
>
> Next, the antenna has a frequency dependent SWR, has anyone put a SWR meter on the coax and measured the SWR as a function of frequency? It should track with the SWR curve for the antenna.
>
> Just my thoughts and I hope that things are going well and getting better for all.
>
> 73s,
>
> kb2bcg at arrl.net mailto:kb2bcg at arrl.net
> -----
>
> On 10/19/18 07:01, Chuck Shefflette via K3CAL wrote:
>
> > > Monica,
> >
> > I’m sure the hardline is good. If I remember correctly it is Andrew LDF4-50B. If it is, and we are really interested in testing it, I have connectors and we could put a connector on one end and have a look at it with a TDR/VNA.
> >
> > Chuck
> > AA3CS
> > ------
> > “There are 10 types of people in this world: those who understand binary and those who don't.” -- Unknown
> >
> >
> > > > > On 17 Oct 2018, at 12:51, Monica < KC3DAS at comcast.net mailto:KC3DAS at comcast.net > wrote:
> > >
> > > Shawn
> > >
> > > Ah!! Thank you for your excellent explanation.
> > >
> > > I'm also thanking Bill for his input yesterday.
> > >
> > > I promise, therefore, not to use the hardline for deer fencing!!! All my plants have been eaten anyway, so I don't need to clean out my gardens!
> > >
> > > Thanks,
> > >
> > > Monica
> > >
> > > KC3DAS
> > >
> > >
> > >
> > > On 10/17/2018 10:18 AM, Shawn Donley wrote:
> > >
> > > > > > > Monica,
> > > >
> > > > The hardline is most likely good. The reason the manufacturer recommends storing on the curved side is that the weight of the hardline can deform the line at the bottom of the spool, particularly in transit. But with a partial spool, this is less likely. Plus the Andrew hardline is more robust that some of the other products. In any case, it's easy to measure the impedance and loss to make sure once a proper connector is installed on one end.
> > > >
> > > > It's possible we may need this hardline to replace the 7/8 hardline (either in part or whole) at Prince Frederick. We know that the 440 antenna system there is bad but until the antenna is disconnected from the hardline, it's difficult to measure the condition of the 7/8" line. Prior time domain reflectometry measurements suggest that the 7/8" line is compromised in some fashion. But there are various stories regarding how the 7/8 was installed originally and if the entire 250 ft length was used or if it was cut and a new connector put on it up on the tower side. So we're not 100% sure if the "bump" seen in the TDR measurements is on the feedline or at the antenna.
> > > >
> > > > IF we don't need the 1/2 inch at Prince Frederick, we'll still need it for the Mt Hope and Barstow shelters if and when the county ever purchases the new AUXCOMM equipment or moves out repeater to the new tower.
> > > >
> > > > Shawn
> > > >
> > > >
> > > >
> > > > > > > > > On October 16, 2018 at 1:28 PM Monica < KC3DAS at comcast.net mailto:KC3DAS at comcast.net > wrote:
> > > > >
> > > > >
> > > > >
> > > > > Per the discussion at the October CARA meeting, some of you were
> > > > > wondering whether the hardline that is stored in our garage was still
> > > > > any good. The spool had previously been stored for quite a while at
> > > > > Mount Hope on its flat end rather than on the curve of the spool as
> > > > > recommended by the manufacturer.
> > > > >
> > > > > What I'd like to know is whether we can test the hardline to see if it's
> > > > > still good or whether it's permanently damaged. If it's not good, I'd
> > > > > like to get it out of our garage. If it's still in good shape, we will
> > > > > keep it where it is. Or if it's good for any other purpose, we would
> > > > > continue to store it.
> > > > >
> > > > > Thoughts??
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Monica
> > > > >
> > > > > KC3DAS
> > > > >
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