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   Home   Help Search  
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Author Topic: Radio choices  (Read 7824 times)
KB1SNJ
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Posts: 114




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« Reply #75 on: October 11, 2017, 08:47:14 PM »

Hi Brentwood Bob, why did you quote Brian's entire text and not post your own message? 

When you quote, I suggest you put your comments outside the quoted text so it's easier to see who said what.

I also have learned to go inside the quoted text and remove anything not related to my reply. This makes the forum much better for reading.

Hope this helps!


Chris
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KM6NFF
Member

Posts: 113




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« Reply #76 on: October 11, 2017, 09:03:53 PM »

Thanks Chris
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K6BRN
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Posts: 450




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« Reply #77 on: October 11, 2017, 10:02:39 PM »

Chris:

The -1K you ordered will do fine on SSB at 100W+ levels and on the high duty cycle JT65, FT8, etc. low-power digital modes, up to about 50W or so.  But when you are transmitting at 80-100 or more watts for long periods, as on RTTY when there is a roundup or the bands simply open up, then the I'd seriously recommend the -2K.

Power and heat is the Achilles heel of end-fed wire antennas.  An EFHW matching transformer is generally one or more stacked toroidal ferrite cores, wound with teflon insulated wire or lacquered magnet wire, with a very high input/output impedance ratio - often about 50:1.  The transformer cores are not 100% efficient and dissipate some of the power flowing through the transformer as heat.  And they are suspended in the center of a sealed plastic box with a very, very poor heat dissipation path.  As you use them, they heat up.  When a portion of the cores reach the vicinity of their Curie temperature, the cores begin to lose their magnetic properties, become less efficient and heat even faster ( a kind of thermal runaway).  The results you will see are SWR that suddenly shoots up from 1.5:1 to 3: 1 to 5:1, etc.  So you have to stop transmitting, let the cores cool and hope you did not crack them.

For that reason, most EFHW antennas are strictly 100W or (much) less ICAS (Intermittant Commercial and Amateur Service), not average (continuous) power.  How ICAS translates into average power is not well defined - but it seems 10:1 to 3:1 ratios are not uncommon.

MyAntennas is one of the few manufacturers that has attacked the EFHW power problem with some success, by using larger cores with a more efficient ferrite "mix".  The EFHW-8010-2K was specifically designed to address the need to run high power/high duty cycle modes like RTTY.  It's transformer takes more power, much longer than any other product I know of.  Is it worthwhile?  IMHO, yes.  The -2K transformer is just a bit larger than the -1K unit, and costs slightly more.  I haven't reached its limit yet.  But I have driven a -1K into high SWR.  So I changed it out with the -2K.

Regarding wires - I have a 2nd home near you in Connecticut.  At that home, I use a thicker grade of antenna wire due to the ice storms and ice loading common to New England winters.  In California, I use the thinner grade - lighter and easier to work with, no ice loading in sunny SoCal.

Is it critical that you change your order?  NO.  But if you would like to hedge your bets against wind and ice, and intend to run higher power, high duty cycle modes in the future, then yes, I believe it's worthwhile.  MyAntennas makes a solid product, and they are not terribly expensive, so trading up later is not really a big deal.  Especially since an upgrade to the wire or transformer will use about the same mounting as the old ones - pretty much drop-in replacements.

Brian - K6BRN
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KF7DS
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Posts: 285




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« Reply #78 on: October 11, 2017, 10:36:55 PM »

+1 on Myantennas...I have the 4010 strung north-south with the feed point at 30’ and the other end at 45’. Works really well and is surprisingly quiet for an end fed.

Don
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KB1SNJ
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Posts: 114




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« Reply #79 on: October 11, 2017, 10:43:02 PM »

Thanks so much Brian, that explains it. I sent a contact form inquiry to MyAntennas regarding my "impluse buy" order. (I've been never really satisfied with the antenna situation since getting my ticket in 2009). I am right now playing with a 9:1 UNUN under a 50ft vertical wire.

With help from eHam community, I made a nice feedpoint choke as well to try and control some RF issues in the house. In fact here is the topic. I am still digesting it all and just now getting back to making the 160M coil for the antenna. (Picture of my DIY choke)
http://www.eham.net/ehamforum/smf/index.php/topic,113083.75.html

I wonder if the choke can be placed ahead of the EFHW feedpoint (I imagine it can) and the copper added for 160M (not sure about that with the end fed because I dont know enough about antenna basics).


One thing about the wire, it appears that all the EFHW antennas use the same 18ga marine "stealth" wire.
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K6BRN
Member

Posts: 450




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« Reply #80 on: October 12, 2017, 06:01:58 AM »

Chris:

Heavier wire is an option listed elsewhere on the site. You'll have to search or ask.   Regarding the RF choke.... MyAntennas recommends inserting the choke in the feedline just before tbe radio.  On tbe topic of extending the EFHW-8010 to 160M... not a practical option.  There is another model tbat covers 160M whose wire is twice as long.  You should already have more than enough bands to work with the 8010, since it covers a number of WARC bands in addition to 10,15,20,40 and 80M.

Have fun!

Brian - K6BRN
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