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Receive Antennas (below 30MHz) - For all topics related to receive antennas used on HF, MW, LW, etc. For transmit antennas use the Amateur Radio Antennas forum.

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Old 03-29-2017, 4:11 PM
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Default toroid material recommendation

Looking at making a 9:1 unun for an antenna to cover the LW and MW frequencies from 100 to 1700, in other words, the LW beacon band and AM broadcast band. Would like recommendation on type of material whether iron powder or ferrite for the toroid (mix or material number).
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Old 03-29-2017, 9:34 PM
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Here is an article I refer to for the frequency range you are seeking: http://www.qsl.net/wa1ion/bev/bb_antenna_matching.pdf
prcguy
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Old 03-29-2017, 10:00 PM
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Exactly the exercise I am doing at the moment except my frequency range is higher. Here is a web page with all the ferrite info..

T44-2

...and you might be interested in this article on the making of different forms of ununs and baluns...

Oops - the link to the web page ran into a dead end so here's the doc.....

...and a pic of my 9:1 unun and choke at the moment! As you can see I went for the quadrifilar winding on an FT-114-43 core. Don't forget to put fibreglass tape over the core, the edges are very sharp. I used very skinny but well insulated wire from a disused printer cable. Have fun!.
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Last edited by majoco; 07-02-2017 at 9:18 PM..
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Old 03-30-2017, 3:58 PM
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wow! tnx guys for all the good tech
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Old 03-30-2017, 9:14 PM
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Thanks for the link Martin, very useful!
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Old 04-12-2017, 9:46 PM
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PRC and Martin,

Was able to put the info in the links you provided to good use and fabricated an antenna incorporating a toroid using #43 ferrite material. Had a chance to try it out this afternoon and it works great! Gave good performance on the LW NDB band all the way through the AM broadcast band. S1 to S2 signals using just a plain wire antenna were S9+ with the new antenna and unun. TNX.
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Old 04-13-2017, 7:47 PM
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Glad you had good results. Did you make an 9:1? How long is the wire antenna?
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Originally Posted by WA8ZTZ View Post
PRC and Martin,

Was able to put the info in the links you provided to good use and fabricated an antenna incorporating a toroid using #43 ferrite material. Had a chance to try it out this afternoon and it works great! Gave good performance on the LW NDB band all the way through the AM broadcast band. S1 to S2 signals using just a plain wire antenna were S9+ with the new antenna and unun. TNX.
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Old 04-14-2017, 6:56 AM
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Quote:
Originally Posted by prcguy View Post
Glad you had good results. Did you make an 9:1? How long is the wire antenna?
prcguy
Wound 12 trifilar turns 22awg on an Amidon FT114-43. Hooked it up in autotransformer fashion so as to create a 36 turn primary and a 12 turn secondary. This was a 3:1 turns ratio which equates to a 9:1 impedance ratio. Secondary was connected across a SO-239 connector. The end fed antenna wire is a 45' length of 16awg MTW (machine tool wire), no special reason for the length, just had it available so used it. Did not bother with a counterpoise or ground, seemed to work fine without. As mentioned, performance is absolutely outstanding compared to just an ordinary wire antenna. For example, heard NDB 362 SB Sudbury ON 300mi from my QTH, a good catch for mid-afternoon. WLW 700 AM Cincinnati, also about 300mi away also mid-afternoon, sounded like a local with a S9+15 signal (have to use an active preselector to get the same result with just a regular wire antenna). Performance begins to drop off above the AM broadcast band but that is OK with me because my intent was to build an antenna specific for LW/MW.
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Old 04-14-2017, 9:51 AM
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Very good on your transformer and that's a lot of turns on the primary, but it also explains why it works well down low where you are using it. For roughly 5 to 30MHz range on that core you would use about 2 turns on the primary.

There is a technique of making the primary a twisted pair on RF autotransformers and that supposedly improves coupling and performance a bit. Here is an example of how the PAR end fed is wound and I do this when making 64:1 transformers for resonant EFHW antennas: https://pa3hho.wordpress.com/end-fed...d-fed-english/

Also, for low power transmit and receive purposes I've been using a single strand of wire from CAT5 Ethernet cable. Its insulation has very good RF properties and its thicker than enamel so you don't have to wrap the cores with tape to protect the wire.
prcguy

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Originally Posted by WA8ZTZ View Post
Wound 12 trifilar turns 22awg on an Amidon FT114-43. Hooked it up in autotransformer fashion so as to create a 36 turn primary and a 12 turn secondary. This was a 3:1 turns ratio which equates to a 9:1 impedance ratio. Secondary was connected across a SO-239 connector. The end fed antenna wire is a 45' length of 16awg MTW (machine tool wire), no special reason for the length, just had it available so used it. Did not bother with a counterpoise or ground, seemed to work fine without. As mentioned, performance is absolutely outstanding compared to just an ordinary wire antenna. For example, heard NDB 362 SB Sudbury ON 300mi from my QTH, a good catch for mid-afternoon. WLW 700 AM Cincinnati, also about 300mi away also mid-afternoon, sounded like a local with a S9+15 signal (have to use an active preselector to get the same result with just a regular wire antenna). Performance begins to drop off above the AM broadcast band but that is OK with me because my intent was to build an antenna specific for LW/MW.
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Old 04-14-2017, 2:18 PM
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PRC,

Tnx, interesting reading.
We must think somewhat alike, just stripped out some CAT5 cable yesterday to get the wire for future antenna projects.
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