rf interference

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
v6a1a4
Posts: 26
Joined: Tue Apr 23, 2002 1:01 am
Location: Vancouver
Contact:

Re: rf interference

Post by v6a1a4 » Tue Aug 16, 2005 9:57 pm

wow, 14 posts and still going strong. I have been gone for a few days so let me try to answer a couple of questions. First of all the product can be found at the following link, http://www.rfdigital.com/item.htm?item=rfd28004
I have solved my problems but I haven't answered my questions.In my line of work you fix and move on, the quickest way. In the process of elimination I did discover a few things. With the relays wired in and nothing wired to the contacts the circuit worked perfectly. With a resistive load like a light bulb wired to the relay contacts the circuit worked fine. With a solenoid wired to the relay contacts all hell broke loose.
Amongst praying, chanting, crying and swearing I tried filter caps in various places, diodes across the relay coils and solenoids, rc networks across the solenoids, ground planes around the Rx and solenoid. Nothing working yet. I tried moving the solenoid away from the rx. This made a difference after about 12 feet which was unacceptable for me. I also tried moving the rx unit away from the relays by 6 feet and this made no difference. I also tried hooking a lightbulb up to the relay contacts, engaging the circuit and activating a solenoid off a completely separate power supply 6 feet away to see what happened. The same interference which caused the lightbulb to flick on and off.
My solution was this. I replaced the relays with some darlingtons and now all is right with the world. Was it the relays, the solenoids or the both of them acting together? I don't know. I would eventually like to figure this out and put relays back in. This would increase the universality of the original circuit but until then thanks for all the good food for thought.
Cheers, James
Vancouver

v6a1a4
Posts: 26
Joined: Tue Apr 23, 2002 1:01 am
Location: Vancouver
Contact:

Re: rf interference

Post by v6a1a4 » Tue Aug 16, 2005 10:01 pm

wow, 14 posts and still going strong. I have been gone for a few days so let me try to answer a couple of questions. First of all the product can be found at the following link, http://www.rfdigital.com/item.htm?item=rfd28004
I have solved my problems but I haven't answered my questions.In my line of work you fix and move on, the quickest way. In the process of elimination I did discover a few things. With the relays wired in and nothing wired to the contacts the circuit worked perfectly. With a resistive load like a light bulb wired to the relay contacts the circuit worked fine. With a solenoid wired to the relay contacts all hell broke loose.
Amongst praying, chanting, crying and swearing I tried filter caps in various places, diodes across the relay coils and solenoids, rc networks across the solenoids, ground planes around the Rx and solenoid. Nothing working yet. I tried moving the solenoid away from the rx. This made a difference after about 12 feet which was unacceptable for me. I also tried moving the rx unit away from the relays by 6 feet and this made no difference. I also tried hooking a lightbulb up to the relay contacts, engaging the circuit and activating a solenoid off a completely separate power supply 6 feet away to see what happened. The same interference which caused the lightbulb to flick on and off.
My solution was this. I replaced the relays with some darlingtons and now all is right with the world. Was it the relays, the solenoids or the both of them acting together? I don't know. I would eventually like to figure this out and put relays back in. This would increase the universality of the original circuit but until then thanks for all the good food for thought.
Cheers, James
Vancouver

Bernius1
Posts: 349
Joined: Sat Sep 21, 2002 1:01 am
Location: NY
Contact:

Re: rf interference

Post by Bernius1 » Wed Aug 17, 2005 10:58 am

Treebeard, I wonder if the circuit is acting like an alarm bell/ mech. oscillator ? What's the resistance of the coil ? Too low, & it may be pulling down the rest of the citrcuit.
Robert,
Light is energy, but not specifically thought of as referenced to a ground plane. With RF, the earth is the other 'conductor'. But signal is peak to peak because it references only to itself. Technically, an antenna coming out of a cap will have an AC signal, but no DC reference potential necessarily. Short story; Video is ~1V P-P ; if your 5V ckt gets locally loaded down to <1V momentarily, the wave will distort. So, if this is a pulsed square wave, and bias/supply problems are changing it to a triangular wave ( bad slew), the area under the curve will drop exponentially, and so will range.
If the light (read prior post ) flickered, maybe what the receiver saw was as if he was hitting the x-mit button very quickly, because at the threshold of energizing the coil, supply + might be pulled down , or waveform sufficiently clipped to prevent action.
My opinion may seem far fetched, but how many 'tough' problems are due to very improbable errors ? I don't disagree with anything you've said. I just know that this isn't a quick "swap the part" fix, and I'm interested in its solution.
Can't we end all posts with a comical quip?

Robert Reed
Posts: 2276
Joined: Wed Nov 24, 2004 1:01 am
Location: ASHTABULA,OHIO
Contact:

Re: rf interference

Post by Robert Reed » Wed Aug 17, 2005 5:54 pm

Treebeard
A couple of quick questions:
Does reciever output operate from momentary action (one quick keyup of Tx), or does the Tx have to be keyed the whole time that output operation is taking place ?
I have been assuming momentary operation up to this point. Constant keyup would change my whole point of view on this subject.<p>
Have you tried contacting manufacturers tech department about your problem?
I called up website on your receiver and its absolutely useless from a specs point of view, so no telling whats going on inside receiver.

v6a1a4
Posts: 26
Joined: Tue Apr 23, 2002 1:01 am
Location: Vancouver
Contact:

Re: rf interference

Post by v6a1a4 » Wed Aug 17, 2005 9:39 pm

If I understand your question correctly Robert, When the key on the key fob is pressed down, a pin on the receiver goes high (+5v). It stays high as long as the key is pressed. When the key is let go, the pin goes back to a ground state. When I say the lamp was flickering I mean the receiver appears to loose contact with the tx and the pin on the rx goes to gnd potential, and them the receiver finds the signal again and the pin goes high. This happens randomly, not any kind of oscillation. Unfortunately I don't have a scope (you keen readers will know this from my other posts :) )so I can't take a look what is going on. When I have time I will come to the bottom of this but for know a am just to have found an alternative solution.
\
Cheers, James

Robert Reed
Posts: 2276
Joined: Wed Nov 24, 2004 1:01 am
Location: ASHTABULA,OHIO
Contact:

Re: rf interference

Post by Robert Reed » Thu Aug 18, 2005 8:53 am

Well , I guess with the limited information we have on hand, we could make assumptions all day long. Unfortuneatly assumptions aren't what you need at this point. Since you have the actual device in hand, you are in the best position to find the problem. Glad to hear you came up with a fix, Keep us posted if you come up for the root of the problem.

Post Reply

Who is online

Users browsing this forum: sghioto and 47 guests