measurement anomaly ?

[Howie Hoyt‏]

I have 480' of lmr600 that has developed a short. 

The shack end measures 1.2 ohms either w or w/o connector.

Likewise the distant end measures 1.7 ohms using a VOM.

Setting the Sark110 to cable test of LMR600, and measuring from the

distant end, markers indicates the short to be 396' down the coax. So far so good.

Now, measuring from the connector on the shack end no indication of a short- just a flat green line out 900x feet. I surmise the connector is ok, as the dc resistance is the same measured at the connector - or removing it and measuring cemter to shield.

Changing to quarter, octave, sixteenth is consistent in showing no short from shack end even tho i measure 1.2 ohm with an ohm meter.

I am left not understanding how I cannot see the short from the shack end- it should be something over 82' from the shack end. 

BTW, the run of coax went down 20yrs ago and tree roots make it a challenge to just pull up the coax.

TIA, Howie N4AF

[Howie Hoyt‏]

[John G3PQA‏]

Most strange.

The TDR function works OK on my 110.

How do you open a .tdr file ?

Top drawer software does not appear to run on my WIN10 PC.

Could you resend it as a normal .csv file that runs on a Sark-110 or Sark Plots?

John

[Howie Hoyt‏]

Hi John -

Wow 14 qsos going back to 1994 on LOTW, which probably means we have qso'd at least 20 times.

Updating SARK to current firmware of 10.26 caused the short dx to change vy slightly,  but still the anomaly of short from distant end and nil on the shack side-completely defies dc ohms measured at both ends. 

I have ordered a NanoVNA to see what it's TDR/FDR reports from the nanovna..I actually have a second Sark110 that has a broken power switch- 

I might short the sw to 'always on' state, just to substantiate the readings coming off the newer S110.

Yes, I will see what I can do to put pdf of the two readings up- if you can imagine it, the reading from the shack end is just a green line w/o bumps.

This feed was to a 80M 4square, but I have circumvented by placing a rcs-4 switch on the feed to 20m ant at base of 20 tower, where 80m ant feed terminates.

Vy 73, Howie

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[John G3PQA‏]

Howie,
Just a thought, maybe wrong, could it be a signal overload from the antenna end?
You could check the TDR function on other coaxes perhaps.

Bad luck over the ON/OFF switch. One has to be very careful with reassembly.  I had to replace the one on my Sark-110. Needs some SMD soldering skills but not that difficult. The switches are available - see Melchor's resources list.
https://www.sark110.com/resources/repairs/replacement-power-switch.

The TDR capabilities of the NanoVNA seem pretty crude compared to Melchor's excellent Sark software for the 110. Personally, even though I can use a NanoVNA I find it a pain to use, particularly outside because the setup is tedious.

Maybe others have other ideas what could cause this anomaly.
A BMP JPG or PDF would be readable. Has anyone seen a .tdr file before ?
73 gl
John

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[Howie Hoyt‏]

Hi John -

I hope these bmp's are ok ?

14 is taken from the antenna end (note- BOTH ends of coax are open/no connection)

12 is taken from the shack end of the LMR600

TIA, Howie

[Howie Hoyt‏]

encl 118' good lmr600 open ends for reference.

tks, Howie

[Howie Hoyt‏]

looking harder at the shack end of the cable, using sixteenth setting, I am thinking I need to cut 3' off the cable and reattach the connector ?

No visible signs but this d/n look right ?

tis, howie

[Howie Hoyt‏]

OK. Whatever problem 2.8' down line was removed and now the short is quite visible on the shack end...

Thanks, Howie