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21
That's an interesting observation, but I suspect one difference is in the definition of "life expectancy" - you are looking at it from a power delivered point of view but length of service is an important criteria.  For example, I imagine most people rate their car battery in terms of how long it lasts not how many amp-hours (number of engine starts) it delivered over its life.  Also, as your calculations show, the numbers change with different depths of discharge - your example showed more power delivered at a 90% DOD versus 50%, but the reverse is true at 30% DOD: 48,000 AHr vs 36,000. 

If we use 100 AHr again, his illustration comparing two batteries at 40% DOD vs. one battery at 80% works out that two batteries at 40% DOD will provide 88,000 AHr over 1100 cycles but two consecutive  single batteries at 80% yields 36,000 AHr each, times two batteries, is 72,000 AHr over 450 cycles.  So running a single battery to 80% DOD to end of life and replacing it gives you 900 cycles and 72,000 AHr vs. 1100 cycles and 88,000 AHr.  It would take 2.44 single batteries to yield the same power output of a pair over its life.  One variable here is: how long is a cycle?  That depends on rate of discharge and rate of recharge. 

I think the take-away from his article and graph is lower DOD is a Good Thing (tm), but beyond 50% the importance diminishes as long as you don't damage the battery.  I have heard the 50% number given as a maximum-do-not-exceed number to prolong life, and the graph seems to reinforce that.  Prolonging life and delivering maximum energy may not be the same thing.

Wally
22
Antennas / Re: The 49:1 Half-Wave End-Fed Transformer Campain is ON!
« Last post by caulktel on August 04, 2018, 05:18:21 PM »
Gil,

I agree, most of these groups have a select few people that like to hear themselves talk and are self professed experts. I have been using EFHW wires with 64:1 and 49:1 transformers with great results for 30 plus years. I continue to use them and will keep using them. As far as I'm concerned, I can't tell any difference between using a 49:1 vs a 64:1 transformer either, they both seem to work equally, just slightly different wire lengths. We use what works, including my Mag Loop which people say is a waste of time but mine works great.

Joel
N6ALT
23
I was reading this article about AGM batteries and noticed the graph relating to cycles and depth of discharge.

http://offgridham.com/2018/03/agm-batteries/?utm_source=amateur-radio-weekly&utm_medium=email&utm_campaign=newsletter

Now what I've always been told is that if a deep cycle battery is discharged bellow 50% you will significantly reduce it's life, ie reduce the number of available cycles. Most plans for how much battery capacity you need figures on discharging down to 50%. So if you calculate that you will need 100ah per day of storage you should buy at least 200ah worth of batteries. This will keep your batteries above that magic 50% number and significantly prolong the life of your batter.

Indeed, the graph does so a sharp change in direction right at that magic 50% mark. But after looking at it for a few minutes, it dawned on me that what the graph is showing is exactly opposite the above premise. To me at least, the graph seems to be saying that the first 50% of your battery is where the number of cycles takes the biggest hit and the second 50% has less impact on the number of cycles available to you.

So I crunched a few quick numbers taken from the graph. If I take a 100ah battery and drain it 50%, I get 50ah out of it per cycle and 700 cycles. 50ah x 700 cycles yields 35,000ah over the life of the battery.
If I only sip 30% off the top I get 30ah per cycle and 1600 cycles. 30 x 1600 is 48,000ah out of the battery during it's life. That's a whopping 52% increase in power harvested over the life of the battery.

On the other hand, if I discharge the battery to where there is only 10% left in it at the end of the day (I'm discharging it by 90%) it still gives me 400 cycles, not that many fewer than only taking 50%. In fact, 90ah x 400 cycles gives me 36,000ah over the life of the battery. That's more than I get when I discharge it down to only 50%.

So the graph is definitely showing that the first 50% of the power taken out of the battery takes the biggest tole on the battery's life. The shallower line means smaller changes in discharge result in larger changes in number of cycles and the steeper line bellow 50% means larger changes in DOD result in smaller changes in number of cycles. If you are going to pull it down to 50%, you are not losing anything to keep on pulling it down to 70%, 80% or even 90%. I wondered if this graph was wrong so I looked for more graphs online and they all say roughly the same thing.

Am I missing something or have I been misled all these years?
24
Antennas / Re: Successful Wire Antennas.
« Last post by Sparks on August 04, 2018, 10:19:01 AM »
Strange, there are 237 pages in that PDF but when I download it I can only look at 145 of them

The PDF is actually only 32 pages long. It starts with the TOC and then moves to Chapter 3 Dipoles, at page 42. Then there are excerpts of other chapters, too. So the PDF is only a sample of the book.

Read more about the book in this review: http://qrznow.com/successful-wire-antennas/

They link to the same sample PDF, except this one has copyright watermarks on every page:
http://www.rsgbshop.org/acatalog/PDF/Successful_Wire%20Ant_sample.pdf

I found the book on Amazon:
https://www.amazon.com/Successful-Wire-Antennas-Ian-Poole/dp/1905086776/
25
Antennas / Re: The 49:1 Half-Wave End-Fed Transformer Campain is ON!
« Last post by gil on August 04, 2018, 05:48:27 AM »
Many of these people have no idea what they're talking about. These transformers do not have high losses. A 240 size core is 90% efficient and a 140 core around 70%. For all practical applications, you'll never hear the difference. What matters is the resonant half wave wire.

Gil.
26
Digital Modes / Re: FT8 digital comms mode
« Last post by vwflyer on August 03, 2018, 08:58:31 PM »
Just a quick anecdote about Olivia. Yesterday, my brother and I were trying to have a QSO on 20 meters over 1500 miles using Olivia, 50 watts and low wire antennas. It was tough copy but we were getting between 50 and 90 percent depending on fades. Shortly after the QSO my brother went outside and saw that one support rope for his G5RV had broken and half of the antenna was laying on the ground. Later he commented that he thought that it was odd that the tuner settings were different than usual.
27
Antennas / Re: Successful Wire Antennas.
« Last post by gil on August 03, 2018, 12:17:05 PM »
Darn. It seems the file is a preview, albeit a large one...

Gil.
28
Antennas / Re: Successful Wire Antennas.
« Last post by caulktel on August 03, 2018, 10:19:38 AM »
Strange, there are 237 pages in that PDF but when I download it I can only look at 145 of them. I really wanted to the section on EFHW's.

Joel
N6ALT
29
Tactical Corner / Re: Sending Encrypted Messages in Morse Code.
« Last post by gil on August 03, 2018, 06:04:23 AM »
Thank you.

Gil.

Sent from my SM-G928F using Tapatalk

30
Tactical Corner / Re: Sending Encrypted Messages in Morse Code.
« Last post by lpwaterhouse on August 03, 2018, 06:02:48 AM »
You're thinking Dual_EC_DRBG, which has nothing to do with AES. NSA only reviewed and approved the AES candidate algorithms, they did not have a direct hand in them like with DES (where they secretly made it more secure) or Dual_EC_DRBG (deliberately sabotaged as part of "Bullrun").

As for 128 vs. 256 the one concern is that 256 seems to be slightly weaker (though FAR from broken) against related key attacks, but given its much greater strength overall I'm not worried by that, both options are sensible, I go with 256 if speed is not a major concern.

If I HAD to pick an alternative today I'd go for ChaCha20 (A Stream Cipher, so not fully comparable), Serpent or Twofish (in descending order of preference), but for the moment I trust AES. Much of that is of course personal preference and gut-feeling, but I read the relevant papers too ;-)
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