Erik_Mag One of the coolest demonstrations is taking a sheet of copper or aluminum with a half-wave long slot cut in it...
A solution to HOAs that's been seen in the ham radio press is to do that with a satellite antenna. While HOAs may restrict amateur radio antennas, they seem to be OK with the small satellite dishes. Apparently they work well for two meters. Don't know if they've been tried for 70cm.
Few people will notice the slot, or the coax that's connected... Even if they did notice the slot, a little non-metallic putty and a fresh coat of paint render that moot.
Back to electrification...
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
timzFound it --
I did not think about damage to the carbon filaments.
Found it -- American Engineer and Railroad Journal (became Railway Mechanical Engineer) for September 1907:
"The choice of frequency was practically fixed by the manufacturing companies within limits of fifteen and twenty-five cycles, and the comparative merits of those two rates only were considered.
"The lower frequency afforded a material reduction in weight, size and cost of motors, a reduction in conductor losses and induction disturbances, together with an increase in the power factor of the motors. Per contra, its adoption would have materially impaired the commercial value of the system as a whole, in restricting or preventing its extension for many other uses incidental to railway operation. The standard power and railway frequency in general use is twenty-five cycles, and as the New Haven Company already owned a number of power houses generating current at this frequency for standard trolley operation, and, in addition, had equipped many of its shops with twenty-five cycle motors, the adoption of fifteen cycles would have required the abandonment of a large amount of standard apparatus, or the interposition of costly and inefficient means of translation. The lighting of stations and other buildings was quite an important factor, as 25 cycles is the lowest frequency at which the carbon filament lamps in general use can be satisfactorily operated. It was also considered desirable to provide for operation in parallel with the 25 cycle generators already adopted by the New York Central Company....
"It was at first proposed to increase the economical radius of transmission to the utmost by generating current at the highest initial voltage for which generators could be safely designed (about 22,000 volts) and to provide substations at suitable intervals, equipped with static transformers, for supplying current at 3,000-6,000 volts to secondary contact circuits....
"It became evident, however, that a great gain in simplicity would result if the intermediate substations and line transformers could be cut out altogether, and further study demonstrated the possibility of effecting this by reducing the initial e. m. f. to 11,000 volts and raising the ratio of the locomotive transformer to correspond. This was carried into effect with a resulting reduction in capital and operating cost, couple with an increase of electrical efficiency, which proved most gratifying. Incidentally, the difficulties in designing satisfactory collecting devices were greatly diminished."
I've played with slot antennas in the past. One of the coolest demonstrations is taking a sheet of copper or aluminum with a half-wave long slot cut in it (easier to do at 1.2GHz than 2M). Place the sheet with the slot between two half wave dipoles, one transmitting and the other receiving. Maximum power transfer occurs when the slot is perpendicular to the dipoles.
IIRC, the old mobile two way radios used dynamotors for voltage step up. A dynamotor is a special M-G set with a single armature with commutators at each end and the high and low voltage windings occupying the same slots in the armature (think DC-DC version of the synchronous converters used for 600V electrifications). The advantages were that the overall device was smaller than an M-G set, more efficient and less sparking at the commutator. The disadavantage is that you had a fixed step-up or step-down ratio.
Dynamtors were commonly used on 600V/1200V interurbans to provide 600V power for lighting and control when running off of 1200VDC. The DL&W 3,000VDC suburban cars used a dynamotor to step 3,000VDC to 1,500VDC for the air compressor.
I can recall hearing the motor/generators in the radios in patrol cars winding up to produce the high voltage necessary to transmit.
Which brings us back to railroads (albeit subways). I have a friend who retired from the NYC subway system as power supervisor. Among the equipment he maintained were the huge motor generators used to convert AC to 600VDC.
As for antennas - how about this one for 2 meters (147 MHz):
It's called a slot cube... You'll have to click on it...
Erik_Mag"Gain" can be a bit ambiguous, whether it is in respect to isotropic, quarter wave monopole or half wave dipole.
Fascinating stuff in the field in the past few years, some of the techniques being things that still look like science fiction after you're shown how they work. And that's just the stuff in the literature...
I've said it before, I'll say it again, I'll never get tired of the magic of radio.
.
blue streak 1 way off topic but the vibrations of car radios before solid state electronics were the cycles of those times. Took up to a minute to amp up the speaker(s) for their rms vibrations.
way off topic but the vibrations of car radios before solid state electronics were the cycles of those times. Took up to a minute to amp up the speaker(s) for their rms vibrations.
I remember often seeing virbrators being sold along with tubes at the tube checker kiosks. Modern solid state equivalent is a switching power supply with synchronous rectification, though these are normally used to STEP DOWN the voltage, e.g. 48V to 3.3V.
Overmod wonder how many understand how effective radative power (ERP) comes about, is calculated, and works ? Its all about the antenna!
(RF power minus feedline and matching loss) times antenna gain. "Gain" can be a bit ambiguous, whether it is in respect to isotropic, quarter wave monopole or half wave dipole.
Paul of Covington... the vibrators in the radios in the cars with 6-volt batteries. I remember seeing a driver banging his fist on the dashboard apparently trying to un-stick the vibrator.
The Panelescent doohickeys were vibrators too, to get battery voltage up to high tension, like a version of the trembler coils in a Model T ignition. Only much, much cruder and cheaper. (Of course the electroluminescent panels did not require any sort of clean waveform -- I forget how they cured the EM interference on the radio. There was a fairly long article in some classic-car magazine about all the ways those things went bad, and how to fix them or replace them (the replacement being the 'done thing' before the value of many of those cars in 'concours' condition went through the roof...)
Ah, the good ol' days!
I thought Blue Streak was talking about the vibrators in the radios in the cars with 6-volt batteries. I remember seeing a driver banging his fist on the dashboard apparently trying to un-stick the vibrator.
And Flintlock, speaking of heaters, I still think of the heater in my '54 Pontiac as the most comfortable design. It was under the front seat and spread hot air onto the floor, warming the feet of front and rear passengers. Later designs blow hot air on your shins.
Does anyone remember the original topic of this thread?
_____________
"A stranger's just a friend you ain't met yet." --- Dave Gardner
How soon we forget! Back in the old days people didn't worry so much about whether the car radio worked as much as they did whether the heater worked! Especially up north, trust me!
I remember a TV car ad from the '60s ( I don't remember which make) where one of the selling points of the vehicle was "...and a heater that WORKS!"
blue streak 1the vibrations of car radios before solid state electronics were the cycles of those times. Took up to a minute to amp up the speaker(s) for their rms vibrations.
... wonder how many understand how effective radiated power (ERP) comes about, is calculated, and works? Its all about the antenna!
The output of the Wilkinson we bought to replace the infamous Collins was nominal 10kW. Our ERP was 17kW, neatly beamed where humans' receivers would pick it up. We could test the emission pattern with an old fluorescent light tube wielded lightsaber fashion; it would light up neatly where the RF pattern hit the tube...
rdamon My head is shaking like a monstable multivibrator
My head is shaking like a monstable multivibrator
rdamonMy head is shaking like a nonstable multivibrator
I tried to just filter this out, but my response fell flat.
If this is part of some kind of plot, it doesn't bode well...
My induction is that I don't have the capacity to take this any more and time to go ohm.
Then there was a story about a diner who was getting fed up with one badly prepared course after another, finally stood up and yelled "What's butter worth to a shabby chef!". (non-EE's probably won't get this)
Warning: There's mho where that came from...
It would have come up sooner than later by someone!
I had actually said 'outer space is so cold that 'resistance is futile' but took it out...
Resistance is futile
tree68Telling this type of joke is punishing work...
Telling this type of joke is punishing work...
NKP guy I'm sure you get a big charge out of these electrifying puns!
I'm sure you get a big charge out of these electrifying puns!
I do! But quite honestly I found it "shocking" that some had to over-analyze the joke! Short-circuits the humor, don't you know?
BZZZZZZZZT!!!
"Ohmmmmm..."
"That's reVolting!"
"Watt did you say?"
That's Watt I like to see, folks getting into the spirit of things and Amping things up a bit!
timz Someone said that 16-2/3 Hz would have been a better choice, except that NH already had some 25 Hz equipment in their shops (or something like that) and that overruled the theoretical advantage of 16-2/3. Edit: I remembered wrong -- it was 15 Hz that they said was better. Maybe Google scanned that issue of Railroad Gazette -- it's on page 177 of the issue for 16 August 1907. Says NH already had "a number of power houses... for trolley operation and, in addition, had equipped many of its shops with 25-cycle motors."
Someone said that 16-2/3 Hz would have been a better choice, except that NH already had some 25 Hz equipment in their shops (or something like that) and that overruled the theoretical advantage of 16-2/3.
Edit: I remembered wrong -- it was 15 Hz that they said was better. Maybe Google scanned that issue of Railroad Gazette -- it's on page 177 of the issue for 16 August 1907. Says NH already had "a number of power houses... for trolley operation and, in addition, had equipped many of its shops with 25-cycle motors."
16-2/3 Hz was the standard traction power frequency in Europe and is better than 25 Hz for commutator motors (closer to DC). 15 Hz would be a bit better, but the only installation using that was the Visalia Electric. The downside of the lower frequency is that the transformers need to be larger (more turns in the windings and more iron in the core).
AC series motors are more expensive, and less efficient than an equivalent DC series motor.
Semper Vaporo NKP guy Flintlock76 "Ow, that Hertz!" Well, I thought it was funny; it brought a smile. But then again, I was meditating. Ohm....................... That's reVolting.
NKP guy Flintlock76 "Ow, that Hertz!" Well, I thought it was funny; it brought a smile. But then again, I was meditating. Ohm.......................
Flintlock76 "Ow, that Hertz!"
Well, I thought it was funny; it brought a smile.
But then again, I was meditating. Ohm.......................
That's reVolting.
Watt did you say?
Semper Vaporo
Pkgs.
Overmodthere was nothing more magical and 'big-time railroading' than New Haven triangular catenary!
I had been told that A.C. Gilbert, whose factory was adjacent to the mainline, got the idea for the Erector Set from the New Haven catenary pole design.
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