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  1. BrianR

    Measuring Distance via Radio Waves

    The key to this is to measure propogation time to 3ns or better and about the only practical way of doing this is by using a carrier modulated by a pseudo random sequence (which as VisiGoth points out results in a spread spectrum signal). Eg a 10 bit PRS at a 5MHz chip rate will do it provided...
  2. BrianR

    How to prevent a triac from causing Incandescents lights to flicker

    Is this a power factor issue?
  3. BrianR

    securing the electrical harness

    Have a look at Digikey and search for "Non-Fraying Expandable Braid Sleeving". This is very similar to a product used successfully on military aircraft harness design. The harnesses are then clamped using rubber or PTFE lined P-Clamps as frequently as needed to keep them from chaffing, but at...
  4. BrianR

    what is this antenna for?

    The VLF antennas in Australia are higher than 100m though, like 300-400m plus an array of surrounding masts to carry the huge top-hat. Quite a few tons of buried copper too to improve ground resistance. Is this one in the photo a broad-band HF antenna. I cannot tell if the guys are active or...
  5. BrianR

    Ti/Ti and CRES/CRES fretting corrosion

    RPstress, I would have thought there was no problem with Cu-Be as long as the Be content was no more than 2% where it will remain in a stable alloy even if abraded.
  6. BrianR

    +/- 270V (540V) supply as opposed to a 0 - 270V supply

    An isolated ground system is an extension of the 2 or 4-wire power systems we have used on some military aircraft to eliminate airframe currents. It sounds like a good idea but there will still be capacitively induced transient and ripple related ground currents so insulation from ground...
  7. BrianR

    Battery Not Holding A Charge

    If the battery is going flat so fast with the ignition off then it implies a fault in a permanently connected load. Burglar alarm, alternator or starter motor for a start. If you can measure the static load current which should be a few mA if there is a burglar alarm connected then try...
  8. BrianR

    Seeking oldest dual-band non-uniform monopole helical antenna

    This was a simple design and I replaced the top section to select a second band. I could have used in-line tuned traps by resonating some sections of the continuous winding and achieved multiband that way but that's not how I did it. I chose to wind the common base section as loosely as...
  9. BrianR

    Lightning Protection, feedpoint? - run to ground in what?

    You certainly have your work cut out for you here. Lightning prefers to strike edges like bluffs so it is a risky position. Do provide the lowest resistance ground possible so if the soil allows it then drive a series of (eg)3 ground stakes as deep into the ground as possible. (A depth of...
  10. BrianR

    Battery Drain / Helper Batteries

    smalldriver, if you are going to measure lead resistance then using an ohmmeter is unlikely to give useful results. If possible measure voltage drop while a certain current is flowing from the battery. Sounds the same but doing it this way eliminates a lot of variables and covers the...
  11. BrianR

    +/- 270V (540V) supply as opposed to a 0 - 270V supply

    I am not sure why you would want to use +/- 270VDC compared to +270V. What advantage would you get? The purpose of using 270VDC is that it is easily obtained by rectifying a standard 3 phase alternator and it does not require speed regulation to maintain 400Hz. The cabling is lighter and...
  12. BrianR

    Seeking oldest dual-band non-uniform monopole helical antenna

    I built my first normal mode multi-band helical in 1970 and they were in comercial use then. I can recall examples from around 1967 onwards. My antenna used fishing rod blanks with a standard base section and replaceable tops. The base section was wound with very heavy wire as it carried most...
  13. BrianR

    xformer o/p w/ cap

    This is an everyday task and if you are not sure what relay/contactor to use then seek advice from your electrical supplier. If transients are a problem fit a snubber or MOV across the load.
  14. BrianR

    xformer o/p w/ cap

    Operahouse, an interesting idea. The peak voltages are generally much larger than 1.4xRMS due to L di/dt and resonance effects.
  15. BrianR

    xformer o/p w/ cap

    Choosing a relay is straight forward provided you understand what the load reactance is. Study the manufacturers data which will typically show that relays rated at 10A for resistive will only be rated at 3A for inductive loads and 3-4A for capacitive. Loads made up of incandescant globes have...
  16. BrianR

    xformer o/p w/ cap

    Adding C causes larger current pulses from the transformer and rectifier which increases heat in the components approx as i^2. nbucksa has given you the accurate equations but I use a rule of thumb to size the C. When 2*pi*f*C*Rl <= 10 then transformer and rectifier heating are tolerable and...
  17. BrianR

    Power Resistor

    This is quite beyond the depth of this topic but I was in the position to take some actual numbers and they might be of interest to others. A piece of steel at 330C radiated 33mW/cm2/sr in 9-12u band and 18mW/cm2/sr in the 3.5-4.5u band. Metal with laquer paint at 40C radiated...
  18. BrianR

    Power Resistor

    Comkid, you're right, the low emissivity of gold makes it a poor radiator but aren't those gold resistors meant to be bolted to heatsinks. The white ceramic ones have a high emissivity, typically 0.9 so they radiate well. It's not always true that black is a better radiator either as surface...
  19. BrianR

    Power Resistor

    I used to use a 2x or even 3x safety figure for power resistors that were in a position to cook things around them. The resistor was in no danger but the radiated heat can do aweful things to stuff placed nearby.
  20. BrianR

    Filtering noise on tip ring line

    If the 60Hz is a differential signal on the balanced line before the transformer, then I don't think you can get rid of it very easily. The transformer should get rid of common mode interference as you said. If however it is induced through that ground connection on the secondary side then...

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