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139
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eHam Forums / Antennas and Towers and more / RE: What does Closed Collinear antenna mean?
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on: September 04, 2012, 07:02:03 PM
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Picket fencing usually doesn't have anything to do with the antenna (unless there
is an intermittent connection somewhere.) Instead it is due to multi-path
propagation.
Hi Dale,
What you say is absolutely true. But I recall a white paper that Motorola did many years ago that suggested a narrower lobe in the elevation pattern may diminish picket fencing as the 2nd signal many times arrived from a higher angle (local building reflection etc). Although I have not modeled the stacked 5/8, I do recall that a single 5/8 has the desired low angle lobe but also a wide higher angle lobe. That's all theory and what happens in the mobile environment may not agree well.
I think of picket fencing when I pull up to a stop light here in the mountans and move forward a bit to get out of what is likely a multipath null on the NPR FM station I listen to.
Dale W4OP |
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140
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eHam Forums / QRP / RE: Let's get something straight about QRP!
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on: September 04, 2012, 05:07:58 PM
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Judging from Four Days in May (FDIM) at Dayton each year, QRP may very well be the fastest growing segment of amateur radio.
And as so many of the QRP gang build, kit and design their own gear, we may be the closest surviving thing to what amateur radio started out as- people interested in wireless, electronics, elmering and building. If we had more of that on the bands today, we would have a lot less "My 1st personal is" and the nonsense of 75M.
Just my opinion,
Dale W4OP
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143
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eHam Forums / Antennas and Towers and more / RE: 80 M Loop Dimensions
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on: September 03, 2012, 04:58:24 PM
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A 80m loop used on 40m will tend to have a null overhead, so won't be as good for local NVIS contacts (out to 100 miles or so). Depending on height above ground, it will be better at 300 miles. It may still be adequate, however. I hope you've read some of the late W4RNL's articles on loop antennas like this one: http://www.cebik.com/content/a10/wire/horloop.htmlThe difference in gain between a 1 lambda round and square loop is less than 0.5dB. And remember, this is the on axis gain- not a very useful direction (for a horizontally deployed loop) for gain except NVIS Dale W4OP |
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144
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eHam Forums / HomeBrew / RE: Newbie MMIC question
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on: August 31, 2012, 09:14:04 PM
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If you are going to send DC out on the coax- that should be fine. But I think the MAR-6 will be driven into IM distortion with very little signal input.
If this is for HF, I would not worry about the cable loss- your noise floor will still be limited by man made, galactic and atmospheric noise.
Dale W4OP
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146
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eHam Forums / APRS / RE: APRS bandpass filter?
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on: August 23, 2012, 09:41:05 AM
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...if it can even be realized... It can, think of a 2m repeater duplexer! Here in the U.S. (from memory) the repeater bandplan has a pair assigned that would require the user to TX as low as 144.520MHz. That's 130KHz above the APRS frequency- well under the 600KHz spacing that duplexers are designed for. In addition, the passband of a duplexer is optimized for a small spectrum- not 145-148 MHz. My company designs some pretty sharp notch filters in small packages- but I don't think you'll see anything with a significant notchat 144.390MHz and yet still have acceptable insertion loss for the repeater band, decent return loss and also capable of handling 50W unless it employs a COR bypass. Dale W4OP |
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148
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eHam Forums / APRS / RE: APRS bandpass filter?
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on: August 22, 2012, 05:52:34 PM
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Unfortunately, the size of a filter for that that narrow a spacing (if it can even be realized) is well beyond anything you would want to put in your car.
Dale W4OP
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149
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eHam Forums / Misc / RE: S-Meter accuracy...LED or needle types
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on: August 21, 2012, 03:08:17 PM
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The Elecraft K3 and its companion P3 can be accurately calibrated to read dBmV. I regularly depend on the P3 for spectrum analyzer measurements.
The only other rig I know of (non SDR) that has a calibrated S meter is the ADT 200A out of Europe.
I am quite sure the HPSDR unit from TAPR also has the capability of absolute calibration.
Unfortunately, the rest of the rigs are a guess and even worse, the preamp effects the S meter reading.
Dale W4OP
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