Simplex Recorder - Surecom SR-112 : Increase Walkie Talkie Range

A Simplex recorder can extend the range of walkie talkies by being a central point to receive a transmission, record it and then re-transmit it.

This project seeks to measure the distances a 0.5 watt walkie talkie can communicate to a simplex recorder attached to a Boafeng 5 watt UV82.

Uniden UH35 (500mW RF Output)

Boafeng UV82 (5 W RF Output)

Surecom SR-112 simplex recorder

Plastic Bag

The Surecom SR-112 simplex recorder was connected to a Boafeng UV85 Walkie Talkie and placed in a bag which was suspended from some branches of a tree overlooking a park.

It was easy to connect up.

1. Select the same channel on the Boafeng and the Walkie Talkie transmitting to it.
2. Adjust the Boafeng's volume so only one set of red and blue lights turn on the simplex recorder.
3. Wait for the re-transmission to the Walkie Talkie.

The first distance test was conducted from outside a brewery 1 km distance away from the Boafeng and simplex recorder, using a 0.5 watt Walkie Talkie. The test message was re-played loud and clear.

Sometime later, further tests were conducted from different locations.

Using a 0.5 watt walkie talkie distance tests to the simplex were done and marked on a map.

Connection could be made up to 2km (4km on resend), depending on terrain (red lines). If there was a hill in the way, even when as close 400 meters away, the walkie talkies couldn't connect (black marks).

I wanted to see if by upping the power to 8 Watts a connection could be made at some of the 0.5 watt 'black spots'. A Baofeng 8 watt walkie talkie was tested. At a couple of spots a connection was made but at most of the others it couldn't be. This was due to the terrain. Both a 0.5 watt walkie talkie and a 8 watt one will not transmit through hills.

The simplex recorder was used on a kayaking trip, the idea being to increase the range of communication if the kayaker with the simplex recorder was in the middle of the group. Enabling people at the rear to communicate with people at the front.

I thought having the message heard when first transmitted and then again when re-transmitted by the simplex recorder may get a bit annoying so a test was done where the re-transmitting was done on a duplex channel. This was achieved by having the connecting walkie talkies tuned to a duplex channel so the message would only be heard once.

A bluetooth channel programming devise (Tidradio model BL-1) with the Odmaster Programming App was used to set up the Baofeng walkie talkie to the opposite of the duplex channels used by the connecting walkie talkies (small 0.5 watt ones). So it would transmit on the channel the small walkie talkies received on and receive on the channel the small walkie talkies transmitted on.

The simplex recorder and Baofeng radio were placed in a 'dry bag' so they wouldn't get wet.

This set up resulted in a lag between messages but no repeated message, it worked well.

On a bush camping trip the Simplex repeater and a 5 watt transceiver were hang from a bush and distance tests made using a .5 watt walkie talkie. The results depend on having a clear line of sight between the walkie talkie and the simplex repeater. A strong signal was obtained from a river 300 meters away and clear communications and after walking up a track 250 meters in the other direction, but once over the crest of the hill, at 600 meters no signal was obtained. In contrast - having driven 10 km from camp to climb a small 'mountain', a clear signal was obtained from the top of the mountain to the repeater - a straight line distance of 6.2 Km away.

If you are interested other ways to extend the range of small walkie talkies check this out. And here's a simple way to make one waterproof.