Fox and Hound Upgrade - Page 1
Forum section: electronics / projects

author: MarkPeeters
author_rank: Newbie
timestamp: August 05, 2020, 08:30:21 pm
content: Hello all,I'm working on designing a fox and hound solution for long range cable tracing, I have reverse engineered a unit and found it just uses a single ended signal and ground. and it uses a 9v battery.I would like to get more distance out of this as I work for an ISP and we still have some copper circuits out there, and are dealing with some long loop lengths that a standard fox and hound doesn't have the reach for.so I was thinking:- I could increase the voltage to get more reach by implementing a boost circuit or even just using two 9v batteries instead of 1- or instead of a single ended signal, make it a differential signal, since that should double the signal level, and it's always a pair of wires.Am I correct that either of these solutions would work? increase the voltage level, and/or make it a differential signal on the line? if so I would implement all of these and be able to switch between them.

author: OM222O
author_rank: Frequent Contributor
timestamp: August 05, 2020, 08:57:33 pm
content: Using 2 9V batteries = fried unit and componentsI'm not sure how those units work, but I'd bet it's not just a "9v battery" across the line. Most likely it uses a specific frequency and looks for that in order to reduce noise. Differential signals can boost your signal integrity, so does reducing that frquency (AC gets coupled to parasitic capacitances and filtered by inductances, whereas DC passes right through). Ideally you'd have a high voltage DC source but if other things are plugged into the line when you connect that, you'd most likely fry something.

author: fordem
author_rank: Regular Contributor
timestamp: August 06, 2020, 01:19:25 am
content: The original Triplett Fox & Hound was an audio signal generator (2KHz I believe) and an audio amplifier with an inductive pickup - I don't recall them having any fancy filtering.An ISP using copper lines - are we talking co-ax, twisted pair or good old fashioned POTs?The old POTs system uses 48v DC signalling so anything connected to it will need to withstand that voltage, for that reason I don't see 2 x 9v batteries as being a potential issue and I don't see differential signalling as being effective for an inductive type pickup as used with most tone tools - the concept behind coax and twisted pair is that both technologies reduce "noise pickup", the corollary of which is "signal radiation" which is, so to speak, equally affected.I don't mean to discourage you, but I've used tone tools from several manufacturers, including the original Triplett Fox & Hound as well as a couple of units from Paladin & Fluke specifically designed for CAT 5 UTP and not one of them was worth a damn in a "live" environment, not even the fancy Fluke Intellitone with digital signalling.

author: MarkPeeters
author_rank: Newbie
timestamp: August 07, 2020, 12:05:14 pm
content: I have build up the reverse engineered schematic I drew up.The system runs at about 1Khz, and it's for the good old pots circuits, and some twisted pair (UTP) as well. The ones I have used in the past don't work well when there is dialtone or battery on the circuit, and the range isn't that far so it's not very usefull for long cable runs in the KM range. all I'm looking for is increasing the range.any ethernet and pots equipment can handle 48vdc without any issues.

author: OM222O
author_rank: Frequent Contributor
timestamp: August 07, 2020, 12:09:36 pm
content: If you post the schematic it could be an easy upgrade: boost converter + replacing the drive element. But like I siad, post the schematic so we're sure.

author: MarkPeeters
author_rank: Newbie
timestamp: August 08, 2020, 01:51:31 am
content: I have attached the current schematic, which is unmodified

author: OM222O
author_rank: Frequent Contributor
timestamp: August 08, 2020, 10:35:08 am
content: it seems pretty basic, just a few oscillators using the not gates. Can you verify that the VCC of the CD4069 is the battery voltage and it's not being regulated?if so just connect the tone out to the gate of mosfet / IGBT (you need to find a high voltage fet since they usually only go up to 20v, not 48). Then connect the source / emitter to GND and connect output of a boost converter set at your desired voltage to the drain / collector. I'd personally go with a fet over IGBT, but I'm not sure about the cost difference of high voltage fets.

author: MarkPeeters
author_rank: Newbie
timestamp: August 08, 2020, 04:00:04 pm
content: The 9v battery is not regulated and connected straight up. The one I reverse engineered is a very old school simple cable tracer and it is one of the best I have ever used, simple and does the job very well.The CD4069 part can run up to 20V, 18V recommended according to the datasheet, hence I was thinking of just doubling the voltage to 18v as an option, should work I think.

author: OM222O
author_rank: Frequent Contributor
timestamp: August 08, 2020, 04:09:43 pm
content: yes, that'd work, however if you want to go higher, you need an amplifier circuit like I mentioned.

author: MarkPeeters
author_rank: Newbie
timestamp: August 08, 2020, 05:13:17 pm
content: For sure.Now that you have seen the schematic, there is also 1 buffer free and available, I was going to use that to make a differential signal, do you think that would increase the range as well, since it should double the voltage again shouldn't it?

author: OM222O
author_rank: Frequent Contributor
timestamp: August 08, 2020, 05:32:10 pm
content: not really, in this case if you increase the voltage on the signal out, it basically has the same effect.

author: MarkPeeters
author_rank: Newbie
timestamp: August 08, 2020, 09:52:55 pm
content: Awesome, thanks for all the information, and help.