Here is a commercial zonar that can boost a smartcast upto 100yds `without` any conversion for 15 quid ,if you require further distance fit an antenna for approx 4 quid for up and over 300yds...cool
This is for existing english frequencies That have had the conversion on the unit display itself..IE,gain antenna!
For all Smartcasts for up and over 300 yards distance boost. for approx 20 quid
I dont usually let out secrets but heres one for the smartcasts owners..cut the antenna tunnel at the top..fit a 1/4 wave 433hz antenna to the spring inside via a socket or permanantly fixed depending on your diy skills...change the batts whenever it dies...change your channel of smartcast to `b` channel and 300 yards is easy!
Enjoy!!!!!!!!!!!
sonar
http://cgi.ebay.co.uk/Replacement-Wireless-Sensor-Sonar-Fish-Finder-433MHz-b0-/230573644161?pt=UK_AudioElectronicsVideo_Video_TelevisionSetTopBoxes&hash=item35af429981"]Replacement Wireless Sensor Sonar Fish Finder 433MHz b0 on eBay (end time 23-Jan-11 16:34:41 GMT)
antenna
http://cgi.ebay.co.uk/1-4-Wave-Whip-Aerial-Antenna-433MHz-BNC-Connection-/150551799873?pt=UK_ConsumerElectronics_SpecialistRadioEquipment_SM&hash=item230d962841"]1/4 Wave Whip Aerial Antenna 433MHz BNC Connection on eBay (end time 27-Jan-11 19:02:38 GMT)
bnc plug if you can solder from spring antenna in duck to the protruding pin on the plug
http://cgi.ebay.co.uk/BNC-FEMALE-RCA-PHONO-MALE-CONNECTORS-CCTV-CABLE-/170560076287?pt=UK_CCTV&hash=item27b62c39ff"]BNC FEMALE TO RCA PHONO MALE CONNECTORS CCTV CABLE on eBay (end time 29-Jan-11 14:33:22 GMT)
then use shrink tube to set antenna to duck antenna stem and your away!

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This one above is the one you want...works spot on with smartcasts on b channel

!