Re: Need some antenna advice (for my CM15A, of course)

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Dave Houston" <nobody@xxxxxxxxxxxx> wrote in message

> Modifying the antenna on a TM751 or RR501 is not something I recommend. It
> can have serious consequences, like DEATH from electrocution.

Do you think that's why they changed the design of the aerial with the
CM15A?  (BTW, what's the difference between "aerial" and "antenna" - or is
there one?)

> You must galvanically isolate any external antenna used with
> these modules as their electronic "ground" is the hot side of
> the 120V mains.

Was that a standard way of building cheap transceivers?  It seems like a
weird way to do things unless it saves a lot of money in assembly or part
costs.

It's not hard to predict that some simpleton getting crappy reception would
open that sucker up and try to attach a wire to the PCB where they assumed
the antenna connection was.  After all, we've seen some pretty frightening
reports from the field here in CHA about what people do with lethal
voltages.  I'll bet more than one poor schlub's gotten a blast of 110VAC
after trying a simpleton mod.

> The CM15A electronics are isolated from line
> voltage so it's safe to replace its antenna.

The modification photos made the CM15A changes look fairly easy, with enough
room inside the case to mount a real "F" type connector.  Damn it Dave, now
I am going to have to go out and buy one of these suckers, if only to avenge
the death of the TM751 I tried to modify!  The pictures at:

http://www.shed.com/tutor/CM15mods/CM15mods.html

make it look *so* easy!

> The thread you cited at AccessX10 is too muddled to make much sense of.

Such is the way with web-based forums.  I am not very fond of them but
sometimes that's all there is.  It's sad that so much of the discussion of
X-10 is taking place elsewhere.

> The MR26A antenna that one poster cited was based on my original
> antenna design for the BX24-AHT.

Was that the twinlead turnstile design found here:

http://www.shed.com/tutor/mr26ant.html

They talk about 50 ohm cable on the drawing but 75 ohm cable in the specs.
Which one is it, do you know?  U

> I've since found the eggbeater to be a better design.

If I understand correctly, your unit had a built-in signal strength meter.
I submit that's really the only way to lend some objectivity to claims of
enhanced reception.  A lot of the posts I've read have been lacking that
real world quantifier:  is the signal really stronger after an antenna
change?  Since you've got an iron-clad way to test for improvement, once
again I have to defer to your knowledge.  How much better is the eggbeater
than the turnstile in practical terms?  Is the BX24-AHT still available
anywhere?

> The CM15A antenna is fixed length and cannot rotate as freely as those on
> the TM751 or RR501. To have it horizontal, it would have to point out from
> the unit and wall.

That certainly undercuts the usefulness of my prior advice!  :-)  (Note to
self:  Restrict commentary to devices actually owned!)

There were some interesting mods listed at that URL that talked about using
model airplane RC antenna tubes to make it possible to position the aerial
more freely.  That looked like a pretty simple mod that I might be able to
do without fouling up.  It does look like there is enough room inside the
unit for even a klutz like me to install an F-connector and putting in a
standard connector seems to be the only way to "do it right."

> Most X-10 receivers have 25-35 foot range. My CM15A range is much greater
> than it was with the OEM antenna.

I don't doubt that.  You're also probably got more electronics skills than
99% of our posters.  I don't want to insult anyone, but a number of posts on
the subject indicate that at least a few others aren't as gifted.  I think
that skill has some effect on the outcome of antenna mods.  That's why I'd
recommend moving the unit around before anything else.  It's a solution with
far less destructive potential than adding a new antenna.  You have
convinced me that a well-executed CM15A antenna mod will seriously extend
the reception range.  I'm just not convinced it's within everyone's skill
set.  :-)

> I don't think much of X-10's software (or firmware) for the CM15A but the
> hardware is excellent. IMO, it's worth a (small) bit of effort to make use
> of it.

Hmmm.  If they start selling them for $25 or so, I might take a look.  I can
see some distinct advantages from the marriage of all-housecode RF with both
PLC and PC interfacing but I've been happy with my relocated TM751.  I
mounted it on top of a tall bookcase in the living room, which is about dead
center for the house and oriented the antenna horizontally.   I also ran a
110VAC line right from the transceiver to the breaker panel which really
strengthened the X-10 powerline signal throughout the house.  Before that
the TM751 was located at the far end of branch that had a lot of appliances
and electronic devices on it.

Thanks for your input Dave, appreciated as always!

--
Bobby G.