LPD Hipo

How to soup up a Conrad radio

The (ahem) quality electronics store Conrad offers a fine Chinese UHF two way radio, known by the Conrad order code 930303, or WT-415B by the manufacturer, Tsuen Shing Electronics Ltd from HK (that's Hong Kong, OK!?!?!?) The manual, so kindly provided by Conrad is for an older version, WT-415 (without the "B"). Now this radio can transmit on LPD (low power device) frequencies, smack in the middle of the 70 cm amateur radio band, or on the PMR (personal mobile radio) band, at 446 MHz. The odd thing is that the PMR permits a power of up to 500 mW while LPD is lopo (low power!) at 10 mW max. How do they do that? In the schematic a weird reference is made to a resistor (Q12) that is actually a transistor. This device switches the bias for the PA. To mod the radio to make LPD hipo (high power for your slow brains) is to disable this transistor. The actual mod was even simpeler...

Void your Warranty

Of course the objective when receiving a new toy is to open it first, even before trying it. This turned out to be not an easy task as the clips in the plastic shell were very stiff. Prying the housing open with a screwdriver next to the antenna solved that. Be careful not to leave any marks in the plastic, but hey, you voided your warranty already anyway :-) Now the radio is open we need to remove the topmost shielding plate that covers the PA. You need solder sucking braid (I use 3 mm "Soder Wick", not a spelling error!) with a medium fine tip on your iron to remove the blobs of solder. Then a thin wire can be connected to the "TX-V+" rail to always bias the PA, which results in hipo on all frequencies, regardless of what the micro wants! The actual connection goes to C30, and the closeups should be self-explanatory. The final pic shows the mod wire poking out from under the reinstalled shield plate (pa6.jpg) with a little notch cut out. The wire I used is kinda like wirewrap wire only the isolation melts if it's heated with a soldering iron. Really handy! Get it at Farnell (I don't have the order code handy, sorry)

Final note

Of course I take no responsibility whatsoever if you fuck up your radio. Also, be advised that you need a license to operate your radio on hipo on the LPD frequencies. Yada yada yada. And yes. I do have a license...