Telcom TE-157 Modification

This page gives a step by step guide for modification of the Telcom TE-157 for HAM UHF radio operation.

The Telcom TE-157 is a low priced PMR radio with 8 channels. With this modification the software is enabled to allowed 69 channels on UHF ham radio ranging 433.075 MHz to 434.775 with 500 mW of power.

If you are not a licenced HAM radio operator theese change will problerly void the legallity and any warrenty of the unit.

Step by step guide to Telcom TE-157 modification

Step 1:
Remove battery cover and batteries.

Step 2:
Remove front cover and then the four screws on the front of the unit.

Step 3:
Remove the front panel and the PTT/Call/Earplug rubber panel carefully.

Step 4:
Remove the two soldered wires marked below.

Step 5:
Carefully tip the main board to the right. Be careful not to break the thin wire to the battery box.
Locate the PTT/Call switch Circuit board and remove the solder from the connection as marked on the illustration below.
The PTT/Call circuit board isthe vertical mounted board soldered to main board.

Step 6:
Carefully tip the display curcuit board to the right

Step 7:
On the display board, locate the 6 linked pads on the upper left side marked 1-2-3-4-5-6.
They are located just below the PTT/Call circuit board. Link 2-4-5 shoud be connected.
Remove link 5 and connect link 6.
When your done, the links should be arranged as the illustration below (link 2-4-6 connected).

Step 9:
Reassemble the unit.

Operation

Push the up arrow and the Mode button simultanious, this will turn the unit on. The Band menu will now appear. Use up/down arrows to select between:

LPD (433/434)
P-K
P-L
K-L
P-K-L
PMR
KDR

Select P-L.

Next you are prompted to select power. Options are Low (10mW) and high (500mW). Chose one and hit Mode to accept changes.

The unit is now ready for operation. If You need to change band you you have to push up arrow+confirm and chose BAND+confirm. Now you can go change between LPD or PMR direct on the fly... (thanks to SM6GOL, Ulf for this tip).

VCO Stability problems (Step 10):
The two units i modified both had the same VCO stability problem.
On UHF (LPD) both transmitter and receiver could not lock on the frequence.
This was confirmed using a frequency counter - the transmitter was all over the band.
Marko, OH2HNW send me a tip for solving this problem.
In the illustration below, located just below the two rubber pads used to hold the loud speaker in place, is located a small coil.
Tightning this coild will help stabilize the VCO.

Links

[2004.01.03]

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