British Telecom 301C "Mole" TDR testers - Photos+Firmware - Page 1
Forum section: electronics / testgear

author: shakalnokturn
author_rank: Super Contributor
timestamp: April 30, 2021, 11:13:39 pm
content: Although there's not much interest in TDR on here it is test equipment.I recently bought four dirty and bashed BT 301C testers for parts on evil bay UK hoping to get at least two of them working.There were two different models, the older version made by Biccotest, the newer by Metrohm.Although the hardware and software differ slightly they must have been designed and manufactured specifically for B.T. they both have the 301C / 315240 model number.The Biccotest model has the most boiled-down UI even if there isn't much between them, the build quality appears much better on the Biccotest units than on the Metrohm, plastic looks stronger, internal graphite shielding, better battery holders, real connector between LCD and main PCB where they're soldered together on the Metrohm.Both hold the firmware in a 27C256, looking through the dumps for text strings shows the Biccotest firmware seems to have been written by "AdTec GmbH" (A www search on this returned nothing).No clues who wrote the firmware for the Metrohm but it does seem to show that it has provision for higher end models including a Spanish market version of the E2770.(The E2770 is meant to have multi-language support, the dump has different portions in English and Spanish suggesting that either the EPROM is truncated from a larger version and/or the software handling at Edgcumbe was a little sketchy.)I got 3/4 of the units working, the Metrohm model has 2 defective lines on the LCD, I was not able to solve this problem that seems to come from the flat interconnect between the PCB and LCD, it was not pressure sensitive on either end. The LED backlights are dead on both the Biccotest units, funnily the electroluminescent one on the Metrohm still works!I have a dirty copy of the user manual for the Biccotest model that I may scan and upload if there's any interest in it.

author: artag
author_rank: Super Contributor
timestamp: May 01, 2021, 08:03:13 pm
content: I have the Bicotest version. Would be interested in reading the manual.

author: cdev
author_rank: Super Contributor
timestamp: May 01, 2021, 08:22:32 pm
content: I would be interested in a comparison between this unit and using the nanovna2 for TDR. (a task which it does pretty well, at least I can tell the distance to a fault in coax, it seems fairly well. )What kind of balun or transformer does it use internally to couple to a pair (balanced transmission line whose nominal impedance is supposed to be, I think, 600 ohms in telephony.)

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 02, 2021, 10:35:12 pm
content: Artag:Attached scanned manual.cdev:I don't own a nanoVNA2 so I can't do this myself.I gave the 301C's a test on 20m of CAT5 Ethernet with the 4 pairs chained to reach 160m, worst case measurement was off by about 10m.These units were adjusted to fit the British Telecom lines of the era not CAT5 so I'd need to recalculate for the right VoP for anything different.No wound balun or transformer to be found at least on the Metrohm model I have left disassembled.The coupling to the line under test is through 100nF MKT capacitors, the rest of what seems to be the fast TDR side of the instrument is plenty of BAT54, two 74HC4316, three OP650U, one 74AC540, one SPT1175 and a (LSI Logic) L5A1564 CPLD or ASIC.

author: cdev
author_rank: Super Contributor
timestamp: May 03, 2021, 01:40:36 pm
content: Your meter's manual looks quite similar in the key apects to what you would do with a nanoVNA2. All he elements are there. Just the nanoVNA is optimized for RF and an 50 ohm unbalanced feed line.The display of the reflection is the same, you determine the velocity factor, and pick a frequency to test it at. The same tradeoffs as to resolution are involved.I am using a homebrew 1:1 balun to match to any balanced transmission line. I use two regular 100 ohm resistors in parallel as my "load" at the output of the balun to establish the calibration plane's beginning, that means I can get accurate readings of the impedance of the whatever (pair of wire) I am using my own clone of the Elecraft BN2 switchable balun, a short is made of a cut piece of copper flashing that fits my baluns binding posts.(its flat) and "nothing" for the open. My balun is designed a little differently than the one in the PDF, which appears to show the origin of the 4-1 mod which Elecraft now included with the balun. I think I have a betterPDF, will upload it. Its very handy.It works well for measurements f distance to faults or changes of any kind of balanced line in the under 60 Mhz range. Good for measuring arbitrary transmission lines like speaker wire.NanoVNA2 was to understate the obvious, aGood dealfor around $70!