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Author Topic: Betty's house  (Read 64209 times)

don hirth

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Re: Betty's house
« Reply #75 on: August 02, 2012, 02:30:51 PM »

. . .Because receiving the 8th harmonic of 3105 kc is even more unlikely, it's worthwhile to analyze the probability that Betty (and Dana Randolph) received a 500 kc transmission, however remote.


Hello Chuck V. 'Very interested in your radio info. I live on the MS. Gulf Coast and 'am "up"
in years but this A.E. search has fascinated me for the last 3 mos......so much so that when finances permit, I plan to purchase a 'decent' transceiver and spend what time I have remaining
communicating with folks. I've been reading a lot about her and radio and when I start, I want to do it 'right' the first time within my financial situation. Well, anyway, hello, again and let's hope
for some great video finds.

John,

Worthwhile?

If you sense some reluctance on my part to pursue what I view to be a pointless exercise, then you’re right. I’ve seen no claim that AE had the capability to radiate a signal at 500 kHz when she departed on her second world flight, nor have I seen a claim that anybody heard a transmission from her on that frequency, or a harmonic of that frequency. Have you?

Quote
Mike Everett's NR16020 radio analysis (and the primary source Gurr/Goerner interview) indicate Gurr integrated a home-made loading coil into the -13C for 500kc operation.  If you have a working transmitter/antenna/atmosphere model, would you please consider estimating Gurr's 500 kc loading coil "power ratio" (for lack of a better term) and analyze the probability of reception?  Yes, we can assume it would be worse than harmonics of 6210 or 3105 kcs, but are we sure?

Here’s a flavor of the problem Gurr faced if he tried to make do with the dorsal V antenna on 500 kHz. Under the conditions I used for estimating behavior at 3.105 and 6.21 MHz, the antenna at 500 kHz has a feedpoint impedance of 0.23 – j 3960 ohms and a radiation efficiency of 5.8%.  (For comparison, I had 1.42 – j 476 ohms at 65% efficiency for 3.105 MHz, and 4.94 – j 27 ohms at 76% efficiency for 6.21 MHz.).

I introduced a loading coil in series with the antenna to get the net reactance closer to the value I had at 3.105 MHz. The last coil design I tried reduced the reactance by 3314 ohms, but introduced more than 4 ohms of additional loss. So the combined loading coil and antenna impedance was 4.3 - j 646 ohms, but had a radiation resistance of 5.8% of 0.23 ohms, or 0.013 ohms. That makes the radiation efficiency of the combined antenna and loading coil equal to 0.3%. If 1 watt is delivered to the combination, only 3 milliwatts is radiated. A new tuning coil design will be required, and it will introduce yet more loss, delivering even less power to the combination.
 
Hopefully you can see that significant effort is required to get an an output power number, and more work is required for each harmonic you want to explore.

I don’t have a propagation prediction program for medium frequencies. If one were to use an HF prediction program you’d need to be at the 5th harmonic of 500 kHz at a minimum, and preferably at the 6th harmonic. Don’t expect much. For example, at 3.105 MHz with a plate output power of 53 watts, the radiated power was 22 watts. The radiated power at the 5th harmonic was 6 microwatts.

Chuck
dlh
 
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JNev

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Re: Betty's house
« Reply #76 on: August 02, 2012, 02:41:25 PM »

Was the 'loading coil' also known to have been removed when they removed the trailing wire?

Jeff,

Well, "known" is a slippery word when applied to equipment aboard the Electra, but with AE's demonstrated penchant for weight saving I'd think that it went when the trailing wire antenna did.

Chuck

Sorry Chuck - didn't mean to put you on the spot.  Allow me to modify my question for clarity -

What information suggests that the coil was removed along with the trailing wire? 

The coil would not have occurred to me as needing to be removed - why would it not just be left in place? 
- Jeff Neville

Former Member 3074R
 
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Chuck Varney

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Re: Betty's house
« Reply #77 on: August 02, 2012, 04:08:28 PM »


Allow me to modify my question for clarity -

What information suggests that the coil was removed along with the trailing wire? 

The coil would not have occurred to me as needing to be removed - why would it not just be left in place?

Jeff,

I guess you’re really asking why I wrote “. . .I’d think that it [the loading coil] went when the trailing wire antenna did.”

Be aware that I’m answering in accordance with an assumption I expressed in an earlier post; namely, that the 500 kHz modification included elements that later appeared in the production 13CB transmitter. I have no documentation to prove the assumption.
 
The subject loading coil was external to the transmitter. It worked in conjunction with the trailing wire antenna and components internal to the transmitter when operating at 500 kHz. With the trailing wire antenna removed, the loading coil served no purpose. With no purpose, it was dead weight. Dead weight was anathema to AE.

Chuck
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John Balderston

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Re: Betty's house
« Reply #78 on: August 02, 2012, 10:01:30 PM »

. . .Because receiving the 8th harmonic of 3105 kc is even more unlikely, it's worthwhile to analyze the probability that Betty (and Dana Randolph) received a 500 kc transmission, however remote.

John,

Worthwhile?

If you sense some reluctance on my part to pursue what I view to be a pointless exercise, then you’re right. I’ve seen no claim that AE had the capability to radiate a signal at 500 kHz when she departed on her second world flight, nor have I seen a claim that anybody heard a transmission from her on that frequency, or a harmonic of that frequency. Have you?

Quote
Mike Everett's NR16020 radio analysis (and the primary source Gurr/Goerner interview) indicate Gurr integrated a home-made loading coil into the -13C for 500kc operation.  If you have a working transmitter/antenna/atmosphere model, would you please consider estimating Gurr's 500 kc loading coil "power ratio" (for lack of a better term) and analyze the probability of reception?  Yes, we can assume it would be worse than harmonics of 6210 or 3105 kcs, but are we sure?

Here’s a flavor of the problem Gurr faced if he tried to make do with the dorsal V antenna on 500 kHz. Under the conditions I used for estimating behavior at 3.105 and 6.21 MHz, the antenna at 500 kHz has a feedpoint impedance of 0.23 – j 3960 ohms and a radiation efficiency of 5.8%.  (For comparison, I had 1.42 – j 476 ohms at 65% efficiency for 3.105 MHz, and 4.94 – j 27 ohms at 76% efficiency for 6.21 MHz.).

I introduced a loading coil in series with the antenna to get the net reactance closer to the value I had at 3.105 MHz. The last coil design I tried reduced the reactance by 3314 ohms, but introduced more than 4 ohms of additional loss. So the combined loading coil and antenna impedance was 4.3 - j 646 ohms, but had a radiation resistance of 5.8% of 0.23 ohms, or 0.013 ohms. That makes the radiation efficiency of the combined antenna and loading coil equal to 0.3%. If 1 watt is delivered to the combination, only 3 milliwatts is radiated. A new tuning coil design will be required, and it will introduce yet more loss, delivering even less power to the combination.
 
Hopefully you can see that significant effort is required to get an an output power number, and more work is required for each harmonic you want to explore.

I don’t have a propagation prediction program for medium frequencies. If one were to use an HF prediction program you’d need to be at the 5th harmonic of 500 kHz at a minimum, and preferably at the 6th harmonic. Don’t expect much. For example, at 3.105 MHz with a plate output power of 53 watts, the radiated power was 22 watts. The radiated power at the 5th harmonic was 6 microwatts.

Chuck

Chuck, this is good analysis - proof that there is no substitute for expertise.  Thanks for that. :)  The six microwatts at 5th harmonic is DISMAL - I'm actually sorry I asked :-[

Re the propagation model, I picked up another reference from the company library today - "Radio Antenna Engineering" (Edmund Laport, RCA Labs, 1952).  Excellent discussion of LF transmission as well as rules of thumb for ground and air propagation.  One of Dr. Laport's rules of thumb is for operator discernment of morse or voice in different conditions (his Appendix VIII).  He states a trained operator needs a minimum signal/noise ratio of about 15 dB to pick out voice.  This is the main reason six microwatts is depressing - probability of reception is infinitesimaly small.  Oh well. 

Thanks again for your your analysis - sincerely appreciated.
John Balderston TIGHAR #3451R
 
« Last Edit: August 02, 2012, 10:18:24 PM by John Balderston »
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