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🔌General Home Automation => Automating Your House => User Modified Devices => Topic started by: Mavrik on May 20, 2011, 11:44:21 AM

Title: TM751 RR501 HC50RX antenna range mod
Post by: Mavrik on May 20, 2011, 11:44:21 AM
I came across this on the web and was wondering if anyone done this mod for increasing the range (adding the capacitor)? What were your results?

http://idobartana.com/hakb/modifying_remote_control_transce.htm
Title: Re: TM751 RR501 HC50RX antenna range mod
Post by: dhouston on June 20, 2011, 06:56:49 PM
I would not do it. The transceivers are not isolated from the mains (that's why the antenna is capcitively coupled through the plastic case) so my advice is to leave them alone unless you know what you are doing.
Title: Re: TM751 RR501 HC50RX antenna range mod
Post by: dave w on June 20, 2011, 08:46:13 PM
If it is on Ido's site, it will work.
However I agree with dhouston. Know what you are doing before going down this road. Also I would recommend only using a cap with a "CS" rating, which unlike standard ceramic caps, will not short. If the cap shorts you will have line voltage on the metal antenna (and in the cramped space in the RR501, shorting from mechanical stress is a possibility). This ain't a part you will find at Radio Shark. Digikey may be a source.
Title: Re: TM751 RR501 HC50RX antenna range mod
Post by: dhouston on June 20, 2011, 09:22:36 PM
A better approach is to use a 75-ohm transformer but you have to be careful when selecting the transformer as many have the primary & secondary commons tied together - you need full isolation. I had a PN for this but lost it (along with a lot more) when I lost a 1TB NAS (Network Attached Storage) HDD a few months ago.
Title: Re: TM751 RR501 HC50RX antenna range mod
Post by: dave w on June 20, 2011, 09:39:23 PM
Quote from: dhouston on June 20, 2011, 09:22:36 PM
A better approach is to use a 75-ohm transformer
What do you do, mount the transformer outside the RR501 case?
Title: Re: TM751 RR501 HC50RX antenna range mod
Post by: dhouston on June 21, 2011, 07:02:32 AM
As long as the transformer has good isolation with no direct connections between primary and secondary, you mount it inside the case and pass the primary leads through the case. Mounting it outside would require passing the secondary leads outside which defeats the purpose by exposing mains voltage.
Title: Re: TM751 RR501 HC50RX antenna range mod
Post by: dave w on June 21, 2011, 11:08:20 AM
Quote from: dhouston on June 21, 2011, 07:02:32 AM
As long as the transformer has good isolation with no direct connections between primary and secondary, you mount it inside the case and pass the primary leads through the case. Mounting it outside would require passing the secondary leads outside which defeats the purpose by exposing mains voltage.


Yeah, thats why I asked. Mentally I pictured a transformer the size of a 300 to 75 ohm balun. Obviously this xformer is much smaller.

Thanks for the information!
Title: Re: TM751 RR501 HC50RX antenna range mod
Post by: dhouston on June 21, 2011, 01:46:27 PM
I'm talking about the guts of a typical balun transformer like these...You'll have to check the datasheets to make sure there's no connection from primary to secondary. And, you need to match the frequency as best you can - these are fairly wideband - X-10 uses 310MHz in N. America but 433.92MHz elsewhere.

You'll need to mount it to a small PCB - maybe some perf board. Insulate it with heat-shrink tubing.\

I picked a datasheet at random to illustrate.You want C where there is complete isolation. These are about 1/4 inch on a side.

Here's one that is even smaller and has 300V interwinding isolation.
I would add fuses (single strand of the finest wire you can find) in both legs between the transformer and antenna. I don't recall whether there's room but you might be able to add a bulkhead coax connector, keeping all wiring inside the case.