General > General Technical Chat
Tektronics 1502 TDR vs. 1503
meballar:
We had a Tek 1502 time domain reflectometer (TDR) in the shop. I had little experience with it, but I soon found out how incredibly useful it was. I could shoot the RF cable at the base of these monstrous LPA antennas and see all the impedance transitions through the 10 connections in the 105' path.
The biggest benefit I found with the TDR is its ability to clearly display sections of water contamination and degraded connections. I don't have any other TDR-type equipment (I read that the Fieldfox has an optional TDR function, but mine only has the CAT). I also have an Anritsu S332D, and like the Distance-to-fault/VSWR function, which I used frequently, along with the TDR.
I encountered some DC voltage when I connected to a wrong port (which had the B+ running through the cable to power the antenna amplifier), which I assume smoked the "unobtainium" tunnel diodes. I think to fix that I'll have to gamble on some of the 1502's on eBay advertised as not working, and hope that there are some salvageable parts.
So I bought a 1503 TDR off eBay, but have found that it is nowhere-even-close to being as useful as my 1502. I don't know the condition of the eBay 1503, but I ran the 1503 diagnostics and it had no errors. The pulses at the high and low impedance parts of a test cable look like what's depicted in the user manual-all I see displayed is an upclock (open) that drops back down to the middle, or downclock (short) that rises back up to the middle .
This is nothing like the display of the 1502's "fingerprint" showing all the impedance deviations (such as the aforementioned LPA antenna sections) within a short distance. When there's an open, the 1502 shows a steep upclock and a high plateau. When there's a short, the 1502 shows a steep downclock and low plateau. But other than those extremes, the 1502 tells a great story: I see a variable impedance over time, indicative of the impedance changes as the cable transitions to the antenna hardware (load coils, connectors, changes in cable impedance (50 ohm cable, to metal airline, to 93 ohm cable, etc.).
Does this huge difference between the displays I'm getting from my 1502 and 1503 suggest that the 1503 has a problem? Would it be a correct statement that the 1503 is more suited for just looking for shorts and opens in a cable path? Thanks for any insights.
Mike
_Wim_:
The 1503B is for longer cable lengths and non 50 ohm impedances. It has 10 times less resolution. Attached a document describing the differences.
tggzzz:
--- Quote from: meballar on November 27, 2022, 05:07:23 am ---I encountered some DC voltage when I connected to a wrong port (which had the B+ running through the cable to power the antenna amplifier), which I assume smoked the "unobtainium" tunnel diodes. I think to fix that I'll have to gamble on some of the 1502's on eBay advertised as not working, and hope that there are some salvageable parts.
--- End quote ---
The 1502s are pleasing instruments, aren't they :)
The TD is even vulnerable to static in the cables; that's why the BNC connector has a unique shorting bar to discharge the static before the core is connected.
I have seen some suggestions that the TD could be replaced by something like the guts of Leo Bodnar's pulse generator http://www.leobodnar.com/shop/index.php?main_page=index&cPath=124 but I haven't seen anybody actually try it.
I have just obtained two non-functional 1502s. With one there's no display and the intensity control shaft is snapped, but ISTR the TD is working. I have choices:
* use it as a parts mule, which might include selling the TD and launch assembly
* find a replacement for the intensity potentiometer
I suspect I won't be able to decide to do the first within a timescale acceptable to you. But if you do get a parts mule, I'm interested in buying that potentiometer.
You could also play with a NanoVNA. It uses an inverse FFT calculation to determine the time domain response.
meballar:
[attach=1]Hello -Wim-,
That is great information, thank you. I did not know anything about the 1503, other than there was an eBay seller that had one for sale, with a picture showing an LMR600 cable plugged into it, and it had the correct vF set up. So it gave me enough confidence that it was working well enough to buy it.
But what a letdown that Tektronix 1503 didn't have the 1502's capability to microscopically look at the RF path! I attached a word doc with a pic of a healthy LPA antenna and pics of degrading issues. Hopefully it will load, since there's no indication that it did, other than selecting the file.
Thanks for your comments.
Mike
_Wim_:
--- Quote from: tggzzz on November 27, 2022, 09:21:35 am ---But if you do get a parts mule, I'm interested in buying that potentiometer.
--- End quote ---
I am interested in buying a display module from a parts mule as my display is turning dark... :D
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