Designing mobile loading coils (they're really inductors) requires both science, and a goodly dose of practicality. It is also a discipline where bigger isn't always better! Here are a few salient points to keep in mind.
As coils get larger in diameter, there is more distributed capacitance, and more resistive wire losses, both of which reduces Q. Thus larger coils have a lower self-resonant point. Above the self-resonant point, a coil acts more like a lossy capacitor, than a coil. Further, anything placed within the coils electrical field will lower the Q. Large metal end caps are an example. And, the size of the wire, the plating on the wire if any, the number of turns per inch (tpi), and the coil support structure (coil form), all have an effect on the (assembled) Q.
Lower frequencies require more inductance in the coil, upper frequencies less inductance. The position of the coil within the antenna's overall length is also a variable, and the optimal position is partially reliant on ground losses. The diameter to length (D/L) ratio increases as the coil's reactance increases. Thus for optimal Q, monoband coils for the lower bands have ratios nearer to 1:5. For the upper bands, the ratio is close to 1:1. This also relates to a maximum overall length of about 15 inches on the lower bands. While monoband coils are still available, the remotely controlled (screwdriver) antenna has almost supplanted them entirely.
Assuming we're using an 80 through 10 meter screwdriver antenna, and you jump through all of the optimal Q mathematical hoops, this is what you'll discover. The coil diameter will be ≈3 inches, wound with #10 silver-plated wire, at 6 tpi, wound on a form with a dielectric constant no higher than 3, and mounted about the half way point or slightly below. The overall length of the coil will hover around 15 to 18 inches, and look just like the one in the photo. Incidentally, the Scorpion 680, and the old Predator use nearly identical coil designs.
Digressing for a moment. It is possible to build a monoband coil with a static Q as high as 450 or so, albeit rather difficult. Once the coil is mounted on the mast, and the top radiator (whip) is installed, the Q will drop. In the aforementioned case, the assembled Q hovers around 250, but may vary due to installation variables (ground loss, shunt capacitance, etc.).
The reason most antenna manufactures don't publish their Q ratings is simply because they're really low—in the 50 to 60 range! Instead, they publish bandwidths which in reality have nothing to do with coil Q. Those that do publish Q figures, often quote the coil's static Q. Once large metal end caps and/or shorting bars are installed, the Q drops drastically! In one well known case, from a static Q of 450, to an installed Q of less than 100! True screwdriver designs suffer less in this respect, unless their coil design is less than optimal as described above.
So how do you know what the assembled coil Q of your antenna really is? You don't! Measuring coil Q once the coil is installed within the antenna, cannot be done. It can be inferred, if you have the test equipment, albeit with poor accuracy. And, A vs. B field measurements are of little value.
SEND ME YOUR PICS
NEW 60 METER BAND FREQUENCY ALLOCATIONS:
PLEASE READ CAREFULLY THE FOLLOWING INFO:
CLICK ON LINK FOR LATEST UPDATE: http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf10623.html
OK the new freq listed for 60m are a little deceiving ,they are listed on the IC site
as carrier freq and I am hearing VE's calling CQ on the freq as listed....
the offset for USB is -1.5kc , ONTARS website posted this to keep us all legal. Thanks to Dave (VE3DV)
AMATURE RADIO TOWER
HEIGHT RESTRICTIONS IN CALEDON
"KNOW YOUR RIGHTS"
This is a story that actually happened to myself the past couple months, I had Caledon Bylaw officer notify me of a complaint from a neighbor on my towers. the town called me in for a meeting to notify me that my antennas and towers were too high, the bylaw on height in Caledon is a MAX of 10.5 meters and were ordering me to take action immediately to correct the situation. i know what it says on Industry Canada's web site and also RAC's web site, but how much is real and how much of this is enforced. Well first thing i'll tell you is that i am glad i am a member of RAC, i did notify I.C and they assigned me with someone who gave me all the info i needed on how to educate the town of Caledon on Federal Government regulations on tower and antenna support structures and the limit of 15 meters is approved for Amateur Radio Operators. needless to say that the town of Caledon refuses to even let me explain my rights even though i shown them my certificate and all I.C info along with a half inch of paper work i copied for them so they could read up on the regulations for Amateur Radio operators. they had no interest in any of my info or my explanations for my station and it's purpose. RAC has since assigned me with a lawyer that is directing me in how this matter should be handled. i have more to tell, but right now i have to hold back as this matter is still being investigated and still might be going to the courts. As info comes my way i will keep you's all posted.
January 24/2014 (UPDATE)
Town of Caledon contact me again today looking for proof of my qualifications and that my certification grants me the rights to over ride the municipality's Bylaws. I took that all to them in a meeting on January 6th, and they refused to see or read any of it. I have today emailed them the exact same copy that Industry Canada emailed to me. now I will wait to see it they read it this time. if this doesn't satisfy them, I will get a Lawyer to send the exact same copy signed by him and see what they say, then if any fee's are added for his cost, we will further action to get these cost covered. will keep you's informed.
know your right's and don't let a neighbor spoil your hobby and don't let a municipality bylaw officer bully you around and try to educate them in how to do there job correctly.
Get a copy at link below.
Rick VA3AGX 15/01/2014
NEWS AS OF FEBRUARY 26, 2014
The town of Caledon has not contact me as my ward councillor has ask them to put on hold till they get up to date on my rights. more to follow.
NEWS AS OF APRIL 23,2014.
Seems all quiet at the fort, maybe the town did there home work and learned a thing or too. I am looking forward to raising the height of my towers to comply with safety code 6. this should give them something to talk about. town representatives should do there home work before shooting off there mouths and scaring people. until next time. 73
NEWS AS OF SEPTEMBER 19, 2015
For those who have been following my battle with some of the idiots who work for the Town Of Caledon. I think they did some reading and learned a thing or to about the rights of Amateur Radio Operator's. They haven't bothered me since I left them with a few comments from advice from my Lawyer. Now that has been settled I have packed up all my station and moved it to my new residence in Kapuskasing Ont. Town of Caledon can keep all there bullshit and the idiot neighbors I had in Bolton.
As for my new location in Kapuskasing, friendly neighbors and loving it up here in the north.
We are sad to announce the passing of a dear friend, Norm Albert Richardson of Englehart Ont, better known to us as VE3NLH/VE3HIQ, has passed away at his home June 6th 2012. his fiance Victoria will keep us updated on funneral arrangements.
more info will be posted as we find out.
a gathering of friends was held on sunday at 3pm at Norms place, but we were already on route to Engelhart when this info was available to us, we appoligize.
Norm passed away in his chair listening to his radios at the short age of 45.
i have probably some of the last pictures taken of Norm from our trip to Dayton Ohio.
i will setup a page in his memory on this site.
below is the last pic i got of VE3NLH & VA3VJS on route back to Toronto.
easy to spot us, 2 PREDATORS chasing each other. :)
Rick & Lucy VA3AGX & VE3LTC
AND THE 350 GROUP