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  #21  
Old 03-01-2011, 11:58 AM
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Originally Posted by rhyary View Post
Oh Gowad. You guys are relentless :-)

No, it was not with the engine running. Ran out side to the parking lot to test with engine running. No apparent difference with engine running or not. Same floor level. The only difference is that you hear the pulsing, but it does not change the floor noise.
LOL! Relentless.

If all you get is S3 with the engine running, that is 4-to-5 S-units lower than me. My truck is an EMI nightmare, the alternator diodes are 21 years old, the ignition overtakes a 50,000 watt commercial clear channel AM station and the CD player turns out not to need an FM adapter... Hams a block away hate me, but I still like my rolling tetanus, radio-black-out experiment! :-)
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  #22  
Old 03-01-2011, 12:24 PM
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Quote:
Originally Posted by Groucho
Dave, the fluoride's getting to you again!
Speaking of which...

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  #23  
Old 03-01-2011, 03:32 PM
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This question of efficiency has been bugging me all day. I think it bears some discussion, although I suspect I will be the only one interested.

I think one of the better (sorta) lay descriptions for efficiency comes from Tom, W8JI

http://www.w8ji.com/radiation_resistance.htm

He says, in part,
Quote:
Folded monopoles provide the clearest common example of radiation resistance misuse. Quite often, in discussions of vertical antenna ground system loss, claims are made that multiple drop wires increase radiation resistance and lower earth or ground system losses. The justification is multiple drop wires, or a folded monopole element, increases radiation resistance. The increased radiation resistance reduces ground currents and ground losses. This concept is justified and/or rationalized through use of the common formula eff % = 100 * Rrad/(Rrad + Rloss) .

Losses must be normalized to the same point where radiation resistance is taken, otherwise the efficiency formula above does not work! Many folded monopole articles either ignore the fact that loss resistances must be normalized to the feedpoint, or the authors are unaware of that rule.
So total efficiency is given by several factors for physically and electrically short antennas, which if you notice means that most of our space limited antennas will have very low radiation resistance but high radiation capacitance, necessitating lots of correcting inductance to minimize antenna reactance.

The definition (non-normalized) for radiation efficiency is given by:
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  • Radiation resistance Rτ
  • Ground-terminal resistance Rg
  • Resistance of tuning inductance Rc
  • Resistance equivalent of insulation loss Ri
  • Resistance equivalent of conductor loss Rw
Notice that ground resistance, tuning inductance and losses all reduce efficiency and so even a physically good antenna is ultimately subject to the same factors as a poor one, which is why when you read eHam you get so many 1-of-5 AND 5-of-5 for the same antenna. Also notice that radiation resistance is both in the numerator and denominator. If you take the time to do good return work, a Hamstick has sufficiently high radiation resistance that it can match fairly closely the performance to higher dollar units. IOW, it's often the care and feeding of the antenna and feed that makes or breaks it and even a random length of wire can work pretty well with the right conditions.

Ultimately, the measure of efficiency, though, is how much power is contained in the generated field vs. input to the antenna. This is where most theoretical efficiency descriptions get sidetracked, because they assume feedpoint characteristics that aren't necessarily true. Anyway, the sure way to include all this theory is to measure power into the antenna and field strength some distance afield. When you do this you defacto normalize and can compare. To which the real world experience of rhyary starts to make sense, what he's doing is simply working pretty well!
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Last edited by DaveInDenver; 06-17-2011 at 12:28 PM.
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  #24  
Old 03-01-2011, 10:14 PM
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Quote:
Originally Posted by DaveInDenver View Post
This question of efficiency has been bugging me all day.. although I suspect I will be the only one interested.



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  #25  
Old 03-02-2011, 10:27 AM
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Default On to 40M antenna

So last night I mounted the 40M hamstick.
I am now getting in to Groucho territory. My noise level sits at S5 now.

The SWR is 1.5 around 7.200 and gets up to 2 around the 7.150. It also get up to 2 when I get up to 7.3. I have work with antenna tuner to see if I can get it better by just adjusting the whip length.

So if I am getting S5 on the 40M, would that be the equivalent of S3 on the 20M?

Does the 40M shows me better the need to do more bonding?

I got the 40M to try night time RF, but I was able to QSO with Wisconsin and Maryland this morning on the way to work.
Wisconsin gave me 5-9+20 and Maryland was 5-7.

Noise is significantly more present than the 20M.

Dave, I do plan to read your efficiency post, primarily to understand the kind of things that bug you :-)
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  #26  
Old 03-03-2011, 01:18 PM
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Was able to QSO with operator 40 miles north of Denver using my mobile 40M hamstick. His signal was 4 7. Mine was reported 5 - 9.
Just saying :-)
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  #27  
Old 04-26-2011, 10:18 AM
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My truck is an EMI nightmare
Made a significant change last night. I installed my common mode choke that uses 50 ferrite beads on a length of RG-58. They are mix #31 and it replaced the toroid I had the HF feedline wrapped around. This morning I gave 40m a shot and nary a tick to be heard, just that blessed sound of the cosmos. Yippee! I'm wondering now if the ferrite I had was maybe not the mix I thought it was now. On 6m the ignition noise is evident but doesn't move the S-meter, which is exactly what I would expect with ferrite #31, that it would be much less effective at 50MHz than 7Mhz.

BTW, heard a Japan station on 40m at 7:15 local. He was obviously having QSO with someone I could not hear, so I didn't burst in. He was only S5-ish, something that was normally swamped.
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  #28  
Old 04-26-2011, 11:21 AM
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Where did you get the ferrite beads? I currently use a toroid like system, but I would love to just hear the cosmos.
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  #29  
Old 04-26-2011, 11:28 AM
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I usually get ferrites and iron cores from CWS Bytemark. Newark carries some interesting ones, although they are not my first go-to. I have also gotten a few from Amidon.

I don't think the key was beads-on-coax, but more the material and the amount of material. There is about a foot and half of beads on the choke right at the radio connector, it's really sorta awkward since my radio is under the passenger seat and the coax is poking out like a tentacle. :-)

I do plan on re-turning the choke using known material toroids or maybe binocular cores and putting one on each connector (probably mix 67 for the VHF) and one at each end of the HF feedline. Putting the choke in or wrapping it with something to protect it from getting broken.

http://www.cwsbytemark.com
https://www.amidoncorp.com
http://www.thewireman.com
http://www.digikey.com
http://www.newark.com
http://www.mouser.com

Common coax cable type outer diameters.
RG-58 is 0.195"
RG-8X is 0.242"
RG-8 is 0.405"
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  #30  
Old 04-26-2011, 01:31 PM
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BTW, if anyone is thinking about an order LMK and we can save some shipping. I need a few parts, but it's no hurry.
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