[Elecraft] Manhattan-style pad capacitance
Geoff, GM4ESD, has asked the relevant question how much shunt capacitance is present in a PCB island when cut with a core drill? I've tried to answer that question with a combination of theory and measured data, which are in close agreement. The details are at http://www.cliftonlaboratories.com/Prototyping.htm#Island_Pad_Prototyping. You can read the entire page, or jump to the capacitance discussion via the in-page link. The short answer to the questions is some and whether some is too much depends on a variety of things discussed in the analysis. I will say, however, that the data has caused me to reconsider using the very thin 0.029 PCB stock for work at higher frequencies, as convenient as it may be for cutting and hole punching. Jack K8ZOA ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Manhattan-style pad capacitance
The link I posted has a direct jump to bookmark and might cause some browsers a problem. The main prototyping page is at http://www.cliftonlaboratories.com/Prototyping.htm and might be a better starting point. Jack K8ZOA Jack Smith wrote: Geoff, GM4ESD, has asked the relevant question how much shunt capacitance is present in a PCB island when cut with a core drill? I've tried to answer that question with a combination of theory and measured data, which are in close agreement. The details are at http://www.cliftonlaboratories.com/Prototyping.htm#Island_Pad_Prototyping. You can read the entire page, or jump to the capacitance discussion via the in-page link. The short answer to the questions is some and whether some is too much depends on a variety of things discussed in the analysis. I will say, however, that the data has caused me to reconsider using the very thin 0.029 PCB stock for work at higher frequencies, as convenient as it may be for cutting and hole punching. Jack K8ZOA ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Manhattan-style pad capacitance
Geoff, GM4ESD, has asked the relevant question how much shunt capacitance is present in a PCB island when cut with a core drill? - I have found that it's useful capacitance at the right times and very problematic at other times. I've never used Manhattan style construction. Years ago I also had one of the drills that produced a round island on pc board copper and, if I wanted, simultaneously drilled a hole in the center for a lead. I used it a lot, but I *never* built a stable, free-running VFO on double sided pc board with that method because the capacitance through the board was sufficient to cause considerable instability in the oscillator's frequency. Circuit board material makes a fairly unstable capacitor dielectric, so the shunt capacitance changed with all sorts of environmental changes. For those applications single-sided pc board was the answer. With other circuits, such as low-level RF amplifiers and even some audio amplifiers, the stray capacitance introduced by the ground plane on the opposite of the board looking at the circuit pad through the board material helped ensure stability at very high frequencies. The board then acted like a low-value bypass connected to every point in the circuit, helping to discourage VHF and UHF parasitics. Manhattan construction would be FB for amplifiers and other things where the stray capacitance might help, but I'd not use that technique to build a circuit where capacitance had to be stable, such as a VFO. From forming pads with the special drill bit I subsequently went on to using a Dremel router tool to grind out copper to form traces on my boards. Works FB for simple boards. Most of my breadboarding on pc material is done using standoff insulators for all circuit points not at dc ground. Such standoffs are plentiful, cheap and tiny: 1/8 watt 10 megohm resistors. Cut one end short, bend it at right angles and solder it to the board at the right spot. Then the lead at the other end is the insulated terminal for the circuit junction. With very few circuits in solid state gear showing an impedance of more than a few hundred thousand ohms and usually much, much less, a 10 megohm resistor is as good as the best insulator in that application. Indeed, a 1 megohm resistor would be as good in most circuits. Ron AC7AC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
