Re: Unusual Challenge

[ABLE1 <somewhere@xxxxxxxxxxx>]

On 10/22/2021 1:18 PM, Jim Davis wrote:
> On Friday, October 22, 2021 at 8:52:59 AM UTC-4, ABLE1 wrote:
>> Ok Guys!!! Here you go. After reading you should
>> be ABLE to get a good nights sleep. :-)
>>
>> And now for the rest of the story!!
>>
>> I had installed this setup in 2013 and it worked great with
>> some minor issues over the years. Batteries, switch, etc.
>> There were some reports of missed signals but was never sure
>> if it was the RF signal loss or the human ear missing the
>> burp of the sounder. It has been just recently that they
>> have know that it has been more of an issue and called me
>> back to help work out a different plan to get the signals
>> better so that they would not miss a customer in the showroom.
>>
>> When I got there last week as I said I checked the batteries
>> and they were a bit low so I replaced with new. Not that it
>> made much difference but it did miss a signal and I thought is
>> was due to the fact that I triggered the door to fast. Assuming
>> that the receiver or transmitter had some delay built in for
>> excessive trips.
>>
>> I moved the transmitter to the shop and it worked every time while
>> there. Placed the transmitter back in the attic above the showroom
>> and I put the transmitter back in the attic above the showroom where
>> it was but staff was in a meeting so I could not test.
>>
>> Was told later that they tried it and it did not work a total of 3 times
>>
>> Now the receiver has a wire about 7" long as a antenna. I have
>> it hanging over the edge of a window so that the walls would not block
>> the RF signal. The Transmitter is in the attic space on a vertical
>> 2x4. The only thing that might block the signal would be the plywood
>> and asphalt shingles on the roof, 70' of distance, bug screen and glass
>> window.
>>
>> Needless to say this is a intermittent problem that is NOW not working!!
>> Now for the revel!!!
>>
>> It was mentioned the the bug screen was a metal mesh type.
>> And I was asked if that could be causing the problem. I said
>> that I did not think it would but, it certainly would not have any
>> bad effects at this time of year to remove the screen. Well
>> they did in the afternoon and did another test and the system
>> burped the horn 13 out of 13 times. ð??® WHAT!!!!
>>
>> They did this with the window open as well. They are going to test
>> with the window shut the next day to see what the results will be.
>>
>> They tested with the window closed the and it worked just fine 5 times.
>>
>> I did some searching online and metal mesh screens as far as I can
>> find are not an issue with RF. That is unless I am involved!!!
>>
>> What I also found out was that this window is where they put a small
>> A/C unit during the summer. Needless to say they have to remove the
>> wire mesh screen to install the A/C and then they re-install the
>> screen when they take the A/C out. If they remember to do so.
>>
>> So this problem is sometimes there and sometimes not there!!!
>> a.k.a. A intermittent problem!! Now SOLVED!!!
>>
>> I strongly suggested that they get the screen frame re-screened with
>> a NYLON MESH screen!!!
>>
>> Hope you enjoyed the story!!
>>
>> Les
> Hmmm
> So - - - maybe making the antenna a little longer so it could stick outside the building would have helped (?)
> .
> Re: The resistor. As I understand it, the closed circuit contact is wired from ground to the trigger terminal. Without a resistor, when the switch opens, the trigger terminal just goes from negative to "float". When you add the resistor, which is wired to the positive terminal when the switch opens, it "pulls" the trigger terminal to Positive. Which is a definite swing from negative to positive rather than to just to a float level. Changing component values on the relay PCB over the years could change the sensitivity level of he trigger input making the relay output of the board a "sometime" thing.
> .
> With regard to the screen affecting the signal, I know microwave ovens utilize the fact that screens block microwaves so you can look inside the oven glass. I'm thinking of a situation that if you had a low frequency transmitter and a receiver and you put one inside and one outside of the building with a metal window screen in between and then - - - still in the line of sight but begin moving one device further and further to the side  - - - the increasing angle would, in effect, make the holes in the screen smaller and smaller. Perhaps affecting the signal.
> Is the window looking straight at the other building or is it off to the side?
> .
> I'm also thinking that I'm putting wireless window transmitters behind casement window metal frame, metal screens all the time with no problems.
>

At this point "since it is working 100%" I choose to leave as is.  If
there is an issue in the future my thinking is that the first will be
to add a piece of Coax to the board, extend to out side and trim off
the outer sheath and braiding for that last 6" to match the existing.
I have done that on other problem child's and it works quite well!!

As for the angle of signal to the screen.

I measured a nylon screen on my deck.  It measured the square of the
pattern at .075" square grid with the bands being .008".
I did a rough angle layout on Google earth and from Tx to Rx Ant. is
about 8.823 degrees.  Plotting out in my CAD as best I can that
angle to the screen grid should not block the RF too much but
it apparently does.  I am guessing that if you add some dirt to
the screen it would block off a bit more and would shave some corners
off the wave length of the RF signal.

In order to get a real block of that screen grid the angle would have
to be closer to 41 degrees.  The only way to verify would be to take
the transmitter and place it at 90 degrees to the screen and see if it
makes any kind of difference.  Well that would be for a lazy day and
a much younger guy to run the test!!  Not me, not now!!

So maybe there is enough signal loss it just couldn't get there.

Thanks for the extra thoughts!!

Les