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Cross Band Mini-Repeater Project
 
Fox Hunt made Easy

 
UV5R, UV82, BFF8, F8HP, UVB5/6 series
 
Note: Testing with BF888S was unsuccessful
Important: This project demonstrates the capability of the radios as a one-way cross-band directional ham repeater. Proper licensing and identification is required when using and testing in this configuration.
 
 
This project shows how to configure two Baofeng radios as:
- Remote Base
- Fox Hunt Transmitter
- Mobile Cross-Band One-Way Repeater
 
 
Requirements

The requirements are Simple. All that is necessary for the initial construction is a pair of Baofeng/Pofung series transceivers and a 2.5mm/3.5mm audio cable.

Connection

The 2.5mm end is plugged into the top jack on the side of the transceiver as shown below. This unit will serve as the receiver.  The 3.5mm end is plugged into the lower jack of the transmitter unit.
Configuration

The VOX on the TX unit needs to be turned ON.
With VOX Level set to 1, the TX will drop approximately 2 seconds after the RX squelch closes. With VOX Level set to 10, the TX will drop immediately upon RX squelch closing.
Adjust the volume from the RX radio to a comfortable level.

 
Added Considerations for Field Operation
To conserve power:
 - turn OFF the ABR (display illumination)
 - turn OFF the Roger Beep
 - use good antennas, such as J-Poles
 - put he RX antenna up about 15' above the TX
 
 
Separation / Isolation

As shown above, one radio must be set to a UHF frequency while the other is VHF for these radios to function with minimal interference The frequencies selected should be set as far apart as possible.
Choose your frequencies carefully and avoid frequency multiples. A signal on 151.0 will be heard loudly on its 3rd harmonic of 453.0 MHz

This applies to the antennas as well. The greater the separation between antennas, the less interference between radios.
 
 
Duplexers  (Two radios using a single antenna)

To operate cross band (VHF/UHF) using a single antenna, a small dual band duplexer such as a Opek DU-500 or MFJ 916B would be required. This allows both radios to use a common antenna without the VHF TX/RX interfering with the UHF TX/RX. This eliminates the separation requirements of two antennas. 
 
To operate both radios on the same band, a single band duplexer must be added. These are much more expense and may be way too impractical for such a simple project.

Most duplexers are designed for indoor or mobile use. Outdoors, they should only be used under good weather conditions avoiding use when there is precipitation.
 
   
Side Notes:


- A "Kitchen Table" test may show the radios appearing to work when both are set in the same band, but in reality, the transmitter will saturate or overload the receiver. This is where field testing comes into play.
 
- Another consideration is Power. Handheld radios have limited heat dissipation and will tend to overheat if used for long continuous transmissions. For long duration use, consider running low power and keep transmissions short to avoid damage to the transmitter.
 
- To legally run as a free standing repeater, the addition of an identifier may be required, depending on your countries regulations. Some countries only require the control operator or licensed operators to properly identify.
 
 
Background and Information
 
More detailed information regarding the general Function and Use of Cross Band Repeaters can be found HERE.

 
Accessories

An accessory that you may want to consider for long duration use is a 12VDC Battery Eliminator. This will power the radios from either a power supply or battery source.
   
2.5mm / 3.5mm audio cable
Audio Auxiliary Stereo Cable

Tip to Tip
Ring to Ring
Sleeve to Sleeve
UV-82 12V Battery Eliminator
  
UV-5R 12V Battery Eliminator

This is meant to be a fun table top and learning project with a practical use and a minimal cost investment.

Auxiliary Station FAQ information can be found here.

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