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Coil Loaded Dipole build - photo diary

Dealer,
No, I wasn't thinking 20 meters. More like, 3 X 3.7 Mhz = 11.1 Mhz.
(Harmonics, the 'odd' multiples tend to 'match' better than the 'even' one, something closer to a low input impedance than the 'even' ones.)
;)
- 'Doc

I don't have an 'Alpha-Delta' antenna. I'm beginning to wish I did so I could do some 'measuring' with it. I'm too cheap and lazy for that, so am enjoying other people doing that 'measuring'! Wouldn't 'hi-jack' this thread for nothing. If I get 'close' to doing that, somebody tell me so I can shut up!
 
Hello QRN:

That might be a good call as the inductance from Moles dimensions figure to 173 uH of inductance. And I figure around 3 pF of Capacatance to get close to 7 MHz, as a resonate LC type circuit.

I guess we need to measure the coils on the antenna analyzer. I wish I had more time.

Jay in the Mojave



QRN said:
Are the coils using distributed capacitance of the turns to resonate the coils and thus are indeed traps? My tribander uses the sleeve casings covering the coils as capacitors to resonate the traps. Could be a similar idea with the Alpha Delta.
Click to expand...
 
I can measure the coils I made easy enough. How do I do it with the analyzer? Just attach a couple of wire leads to the balun and put each lead at each end of the coil?


In response to John's question about the tag ends, according the AD instructions for their antenna you adjust the main wire first for 40m, then adjust the tag ends for where you want the lowest SWR for 80m.
 
moleculo said:
I can measure the coils I made easy enough. How do I do it with the analyzer? Just attach a couple of wire leads to the balun and put each lead at each end of the coil?


In response to John's question about the tag ends, according the AD instructions for their antenna you adjust the main wire first for 40m, then adjust the tag ends for where you want the lowest SWR for 80m.
Click to expand...

____________________________________________________________________________

Thanks for that Information on antenna.

The MFJ-66 may be what you need $24.95 or the whole kit, MFJ-99 for $60.85
which also includes the Carrying Case and Power Adapter for the 259B

I use my 269B with a 12 volt adapter I made, or the Power Adapter when possible.

The higher voltage seem to make the readings more stable and precise...

Dont ask why I gave away the coils in 2004 to a local :( He went SK in 2005.

I guess tomorrow I will check to see if his wife has any of his stuff...

BTW: I still have the Manual, also think you could download it from their site
to check and see if it is what you need.


Regards,
John
 
Hello Mole:

Disconnect the coils from the dipole wire, and connect the coil to the SO239 connector.

In the Xl mode the coil should be measured around the 40 meter band, and a high XL measurement, I would think. And what frequency has the highest Xl.

Jay in the Mojave


moleculo said:
I can measure the coils I made easy enough. How do I do it with the analyzer? Just attach a couple of wire leads to the balun and put each lead at each end of the coil?
Click to expand...
 
Just attach the center coductor to one side of the coil? Don't attach the ground side to anything?
 
OK, I did it that way already, but I used a 1:1 current balun attached to the meter with two wire leads coming off that to the coil to measure it. When I do that, the meter reads: L(Z>650) at 7mhz, meaning it's out of the range the meter can measure. I'll do it again and move the frequency higher until I can get a reading for comparitive purposes.
 
I tried using the MFJ-259 and it just wouldn't give a good reading. It varied wildly depending on how I held it, where my fingers were, which way the wind was blowing, etc.

So instead I got out my digital calipers, took measurements and punched in the info to an online inductance calculator here:
Martin E. Meserve - K7MEM - Coil Inductance Calculator

I used coil diameter of 1.9", coil length of 4.9" and number of turns = 65 to get an inductance of 66.257uH. Incidentally, the coil spacing that it calculated is exactly what I measured as the outside diameter of the jacketed wire, so that seems like a good formula to me.
 
One thing I just checked is that on the link I posted earlier, the author VK3CAE said you need to get inductance of about 65uH to make it work on 80m, which will also result in the inside/main wires being a 1/2 wave dipole, not seeing past the coil. It looks like I got pretty close to that figure by coping Alpha Delta's design. The slightly larger coil and slightly more spacing on mine made up for a couple fewer turns.

As a side note, the I also measured the wire guage which is 22ga.
 
Yep, it's finished. I cleaned up the wire ends that are attached to the coil by adding terminal lugs on it and double-checked the wire lengths. If you're going to feed it with ladder line, you'll need to use a balun and tuner. If you use coax, you can make it resonant on 40m & 80m. I don't think I would try to tune up 10m & 20m with coax, though.

I did a thread around Thanksgiving where I showed it in action:

http://www.worldwidedx.com/amateur-...-new-40-80-meter-doublet-rv-station-pics.html
 
Check it out
 

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