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By Sponsor
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By WelshPaul
Repurposing a 20th Century British classic for the new millennium.

The GPO746 is loved by many – it’s hard to ignore the classic look and high quality construction of the original — but with most of us now using VoIP it is often left to sit there as an ornament and gather dust. But we can give it a 21st century upgrade!

The GPO poses a few challenges for VoIP hardware enthusiasts. First, it requires a ring capacitor to drive the bells when it rings. Also, the GPO is a rotary dialer, which most modern ATAs don’t support. But where there is a will there is a way, and here I will offer detail on two approaches that can be taken to ready this classic for the world of IP.

The Easy Approach

The easiest way to get your classic phone to work with VoIP is to plug all the adapters inline, external to the phone. To convert the rotary dial clicks into DTMF you can use a Dialgizmo, a device that sits inline between the ATA and the phone. It works well, though it will occasionally detect the hook flash as a “1” and send the DTMF so you need to be careful when taking the handset off hook.

Along with the Dialgizmo you’ll need to find a ring capacitor. You can either purchase an inline ring capacitor from an online store, or you can repurpose a master socket if you have one lying around.

Finally you’ll need an ATA.

The GPO746 plugged into a re-used master socket, which in turn in plugged into the Dialgizmo, which is plugged into an Obihai OBi202 ATA.

Using this simple conversion approach you can get your classic phone working over VoIP. But you want a more elegant solution, I hear you say?

The Advanced Approach

You say you don’t fancy having a string of adapters connected to your classic phone? Well, if you are handy with a soldering iron, the Rotatone offers another method, an integrated solution, installed inside your GPO746. And if you’re not handy with a soldering iron, don’t worry – they also have a service where you can send in your classic phone to have the Rotatone and a ring capacitor installed (after making a ham-fisted attempt at soldering — It’s been many years — I chose the send-in option).

The Rotatone is the black box on the left. It is wired between the rotary dialer and the control board of the GPO746.

The Rotatone has the advantage of not suffering from hook switch triggering DTMF tones, and having the ring capacitor installed in the device also removes another item from the daisy chain between the phone and the ATA.

So how about we go a step further an install the ATA within our classic phone as well!

The OBi200 (and OBi300) ATA both fit perfectly between the hook switch of the GPO746. If we remove the line cable from our phone we can wire this plug internally straight into the back of the ATA and route the power for the OBi via the line cable’s port. Rather than drill into the case to create a hole for an Ethernet cable we can instead plug an OBiWiFi adapter into the back of the ATA to allow it to operate wirelessly.

Everything installed inside the GPO746.

We now have our WiFi-enabled GPO746 IP Phone, repurposed and ready for the 21st century. And you can even take it a step further by installing an OBiBT USB adapter into the USB port. To do this you’ll need to use a USB hub to allow plugging the OBiWiFi and OBiBT adaptors into the one port. If you can find a place to squeeze that in you will have a GPO746 that’s not only wireless but that can also pair with your mobile phone via Bluetooth.

So what are you waiting for? Winter is just around the corner, and there are few better excuses for spending an afternoon converting your phone in a small room filled with solder fumes. Best of luck!



By Sponsor
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By testerworthy

I have just seen that BT intend to switch off the PSTN in 2025. There are many old people (my mother included) who only have analogue telephones, many still having the good old GPO 746 , of course. There has been no significant information on this and many senior citizens will be caught out (I'm surprised that Age UK hasn't picked this up yet). Will BT be supplying ATAs (at their cost) and sending out engineers to change all these phones over? I only got my landline upgraded when the superfast broadband router started 'playing up' after 6 months of going over (at BT's cost). Your comments will be appreciated.
User avatar
By WelshPaul
testerworthy wrote: Fri 3rd May 2019, 10:05Will BT be supplying ATAs (at their cost) and sending out engineers to change all these phones over?
Who knows! It's likely that BT will supply routers to their customers that have a VoIP ATA built in and as most VoIP ATA's don't support pulse dialling, it's unlikely that BT or any of the other telco's would include one that did. As for setup - One would simple plug their telephone into one of the phone ports on the rear of the router.

It is still possible to convert older rotary phones to work with touch tone only landlines / VoIP hardware... I recently purchased a GPO 706 from eBay and while I can dial out on a BT PSTN line, I cannot dial out on my Virgin Media PSTN line as Virgin Media do not support pulse dialling. As for using it with VoIP - I have successfully used alongside a Grandstream HT812 ATA (supports pulse dialling) but not with any of my other ATA’s (Cisco, Linksys and OBIHAI). Oh, and don't get your hopes up about the possibility of using your own ATA as with any of the major Telco’s as they are sure to use hardware that has been locked down tighter than a frogs behind. All is not lost though - I purchased a RotaTone from https://www.rotatone.co.uk and installed it on my GPO 706 and it now works on any VoIP ATA / PSTN line as it now sends out the required touch tones. :ok_hand:

OK, while installing the RotaTone on my GPO 706 was a pain in the behind it does allow one to continue to use old hardware alongside newer technology.

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