On Fri, 16 May 2014 11:01:42 -0400, "Michael A. Terrell"
wrote:

If that were true, you would know how sensitive the front end is to
detuning. The additional capacitance of coax would take it out of band
without reducing the inductance in the tuned circuit.

That was certainly true of previous generations of remote control
receivers. I fixed a few of those (mostly by retuning). Most of the
few garage door and gate opener repairs I've done have been
mechanical, not electronic.

Times have changes. For keyless entry receivers, I'm seeing SAW
filters, superhets, one-chip receivers, etc. For example:
http://www.maximintegrated.com/datasheet/index.mvp/id/3104
http://www.maximintegrated.com/datasheet/index.mvp/id/5513
etc...

Whether Genie uses technology that's become standard for automobile
door openers and alarms is unknown. Schematics seem difficult to
find. Most of the receiver pictures of the boards I've found are
obviously TRF (tuned RF) receivers, which will have the detuning
problems you mentioned. The more modern opener that Jim bought seems
to have a more sophisticated receiver:
http://galleryplus.ebayimg.com/ws/web/301060926645_1_0_1/1000x1000.jpg
The black wire on the left is the antenna. Most of the receiver is
covered but I can see the leads of an SOT device nearby and no
adjustable coils near the antenna lead. That suggests a more modern
design, probably using one of the aforementioned integrated receivers,
which will not have antenna detuning issues.

BTW, I repaired
hundreds of the damned things for a garage door company that was owned
by a friend. I repaired stuff from early tube designs, up to rolling
code. From single function, to specials models that controlled eight
doors for firehouses.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558