@SteveG posted:Thanks for the informative reply!
For another 30-11024 block signal I've never used I'm going to look for the timer with relay in option 2 as it seems a simple and cost effective solution. I have a 12V DC adapter that I will use as the power source.
For my existing block signal I have an old Radio Shack 275-206 relay (12V DC, 3 A, I believe 160 ohms) and a full wave bridge rectifier with the + of rectifier going to + coil of relay and - of rectifier going to - coil of relay. The signals do work correctly.
The problem is I get chatter if the wheels are even slightly dirty. I have a 1000 MFD 35V capacitor across the relay coil with - to -, + to + but I get no delay in signal changing and I get the chatter. I already had this setup in a previous layout several years ago and it worked fine, so I'm wondering why the chatter is there.
I also added 33 ohm 1 W resistor to the wire going to isolated track which I've seen in several threads for this arrangement to eliminate sparks on the wheels. Did not add a diode, but I have some available if needed.
OK, so I'll do the math here in "real time" not knowing the answer!
A 1000uF capacitor charged to 10.7V has 1/2 * C * V * V = 0.06 Watt-seconds (Joules) of energy stored. If your 12V relay coil is indeed 160 Ohms, that suggests the coil power is V * V / R = 0.9 Watts. That means, ignoring the geeky physics of how capacitors discharge, your capacitor can "power" the relay coil for at most 0.06 Watt-sec / 0.9 Watts = 0.07 seconds. 0.07 seconds is not even a tenth of a second so I can see how that would not be enough to cover for dirty/intermittent wheel-track contact. I like to budget 1/4 second (or more) of time for wheel/track chatter suppression so the signal head does not flicker red-green-red-green. Your mileage may vary!
If you're game to try the timer I show, I know exactly how to program it for what you want. It has a plethora/multitude of timing modes; you want "mode P1.2" which I realize makes no sense until you read the instructions. Then set the time delay to 5.0 seconds or whatever (I'd think you want something shorter like, say, 1.0 seconds but whatever works for you). It appears like you know your way around wiring and such but I can draw you an exact wiring diagram if that helps.
The timer is widely available on eBay, Amazon, and so on. You can save a few bucks if you don't mind waiting for shipping from Asia (2-3 weeks).
As to Option 3, for those wanting to save yet a few more bucks, the "trick" with the low-cost eBay/Amazon relay modules is the trigger input does not directly drive the relay coil like your bare-bones Radio Shack relay. There is a transistor amplifier/buffer which reduces the trigger power by at least a factor of 10. So in an apples-to-apples comparison, that same 1000uF cap that only kept your Radio Shack relay going for less than a tenth of a second would keep it going for over a second. Again, this method requires fussing at the component-level and there are i's to dot and t's to cross but if inquiring minds want to know I can dig up some relevant OGR thread(s). 
