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

[nobody@xxxxxxxxxxxx (Dave Houston)]

It gets too confusing for us geezers to try to respond inline so...

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!