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public:blog:antenna_changes [05/07/26 08:52 BST] – created johnpublic:blog:antenna_changes [07/07/26 10:04 BST] (current) – [Antenna Changes] john
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 ====== Antenna Changes ====== ====== Antenna Changes ======
  
  
 Now that I'm turning my attention back to QRP I decided that the antenna I've used for many years - an Inverted-L held up by (over the years) different supports, and currently a 10m SOTA-pole with the top few sections removed - tuned against a mess of radials and ground rods by a CG-3000 Auto-ATU - was due for a change. Now that I'm turning my attention back to QRP I decided that the antenna I've used for many years - an Inverted-L held up by (over the years) different supports, and currently a 10m SOTA-pole with the top few sections removed - tuned against a mess of radials and ground rods by a CG-3000 Auto-ATU - was due for a change.
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 +=== ===
  
 The Auto-ATU needs "a few watts" to trigger a re-tune on a new frequency. Occasionally it'll work with 5W but not consistently, and certainly won't re-tune at anything lower than 5W. This means occasionally having to give it a carrier from a QRO radio to re-tune before switching to a QRP radio.  The Auto-ATU needs "a few watts" to trigger a re-tune on a new frequency. Occasionally it'll work with 5W but not consistently, and certainly won't re-tune at anything lower than 5W. This means occasionally having to give it a carrier from a QRO radio to re-tune before switching to a QRP radio. 
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 This removes the need for a good, low impedance ground connection and simplifies things. It also means "more wire" in the air for each band. This removes the need for a good, low impedance ground connection and simplifies things. It also means "more wire" in the air for each band.
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 +===== First Step - EFHW for 30m  =====
  
 I removed the Auto-ATU and put my nanoVNA on the current antenna/ground feed point to see what I've got now (a totally random length). The first resonance/low SWR is around 3.2MHz. That means a 1/4 wave at 3.2MHz or around 23m. I can perhaps squeeze a little more wire into the space but I'll accept that the new antenna overall length will be limited to "around 23m". I removed the Auto-ATU and put my nanoVNA on the current antenna/ground feed point to see what I've got now (a totally random length). The first resonance/low SWR is around 3.2MHz. That means a 1/4 wave at 3.2MHz or around 23m. I can perhaps squeeze a little more wire into the space but I'll accept that the new antenna overall length will be limited to "around 23m".
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 No need for an ATU (auto or manual). No need for an ATU (auto or manual).
  
-Next step - make trap for 10.1MHz and add it to the end of the current antenna, then add wire to make a dual-band 30m / 40m antenna. That should cover my normal CW operations for a while.+===== Next step - trapped EFHW for 2 bands - 30m & 40m =====  
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 +I made a trap for 10.1MHz and added it to the end of the current antenna, then added wire to make a dual-band 30m / 40m antenna. That should cover my normal CW operations for a while. 
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 +{{:public:blog:30mtrap1.jpg?direct&600|}} 
 +{{:public:blog:30mtrap2.jpg?direct&600|}} 
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 +I found that adding the trap and additional 40m section caused the the 30m resonance to move up about 200kHz, so I had to add about 12" of wire to the first part of the antenna to bring it back down into band. Otherwise it was a simple to add the trap, add the extra wire, trim the far end to bring the 40m resonance into band. 
  
 I'm thinking of also trying to get 60m, but a 1/2 wave on 60m is around 30m and won't fit in the space - UNLESS the loading effect of the 30m and 40m traps, below their resonance, will add enough inductance shorten the required wire length sufficiently. I'm thinking of also trying to get 60m, but a 1/2 wave on 60m is around 30m and won't fit in the space - UNLESS the loading effect of the 30m and 40m traps, below their resonance, will add enough inductance shorten the required wire length sufficiently.
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 +~~DISCUSSION~~