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

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Dave Houston" <nobody@xxxxxxxxxxxx> wrote in message
news:428fdbe8.128494733@xxxxxxxxxxxxxxxx
> It gets too confusing for us geezers to try to respond inline so...

OK - I'm sorry.  I'm never quite sure what netiquette rules are in forces.
In some places I would be branded a stinking top poster for answering like
this!  :-)

I've checked out the links.  Thanks.  And thanks for the answers, which
stand without much comment.  I think I'll wait until the CM15A's been around
a little bit longer to let them get the kinks out

--
Bobby G.

> Follow the links on my CM15A page www.mbx-usa.com/cm15a.htm, one of which
> will eventually lead to...
>
>      http://accessx10.com/howto_fconnector_page1.html
>
> which has much clearer pictures. As I note in the text on my page, I
> recommend using a 50-ohm BNC connector and 50-ohm coax (RG58/U). I buy it
> with preassembled BNC connectors.
>
> The RSSI measurement of the receiver linear output made with the BX24-AHT
> wasn't really useful for making definitive comparisons between antennas
> because the RF receiver module had AGC which reduces the gain as the
signal
> gets stronger. It was useful for fine tuning the receiver. Lacking
expensive
> lab style equipment, the most reliable measurement is to compare range.
>
> People who built the BX24-AHT found they got excellent range with either
the
> turnstile or the eggbeater. My experience was that the eggbeater was a bit
> better. It's easier to construct and needs no balun but the 93-ohm coax
for
> the phasing line is not easy to find. You can cheat and use 75-ohm without
> too much of a penalty. One person who built it with 12 gauge insulated
solid
> copper wire, a 75-ohm phasing line and the TenTec preamp got 175+ feet
> through several walls in his condo complex. I've measured 200+ feet here.
>
> The BX24-AHT plans, part lists, schematics, firmware and software can all
be
> downloaded from my web page but there is no source right now for the
boards.
> My health is too iffy so I don't have plans currently to make the boards
> available again.
>
> All X-10 made mains modules, except for those with RS-232 or USB
interfaces,
> use the hot side for electronic ground. I think it has to do with noise.
The
> serial interface requires isolation by UL. That's why the design is
> different for the CM15A.
>
> They also used third party RF components which was probably done for cost
> reasons. They are dirt cheap from China. (I paid under $2 each for SAW
> controlled RF transmitter modules in fairly modest quantities.) You can
even
> get boards made there in very low quantity and shipped via FedEx with
about
> a 10 day turn around.
>
> Aerial and antenna mean the same. Aerial tends to be used in Europe while
> antenna is more common here.
>
> X-10 has a forum for the CM15A and I think most of the discussion about it
> takes place there. I'm not sure that's a good thing but I'm sure X-10
thinks
> it is.
>
> "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:
>
> >"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!
>