Greg T
WDX-945 (Jazz Singer) Upper Peninsula of Michigan
"Upgrade"? There is no mobile upgrade over a 1/4 wave whip.
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Mobile 102 Inch Whip w/spring
- Thread starter GLM927
- Start date
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- cb antenna cb antennas triple
As has been said there is no upgrade over the 1/4 wave whip, anything with a coil is a downgrade.
you have to call or text him to get in touch, or facebook. his mobile antennas are a sloppy build in my opinion. no machining, just welded on nuts and bolts with oversized sloppy welds. bleh
Your screwed if anything on that breaks.
At least the Predators you can replace parts.
73
Jeff
If the magnet foil area (assuming foil and coax shield are well connected) is 22 square inch, the paint is 60 micron thick, and the average dielectric constant of that paint is 4.68, the capacitance is 9.8nF. At 27MHz, that represents 0.6Ω reactance.
Not only is that triple mag mount an effective ground, that 700w isn't going to even come close to arcing through the paint because the voltage across that capacitance is, at most, the square root of (700w x 0.6Ω) = 20.49v RMS. Edit: I think its more like sqrt(350w x 0.6Ω)=14.5 because half the power is moving electrons in the whip section..
If you do not know whether or not your foil is well connected to the magnet mount itself, its best to just tear it off and redo the foil with copper tape.
Not only is that triple mag mount an effective ground, that 700w isn't going to even come close to arcing through the paint because the voltage across that capacitance is, at most, the square root of (700w x 0.6Ω) = 20.49v RMS. Edit: I think its more like sqrt(350w x 0.6Ω)=14.5 because half the power is moving electrons in the whip section..
If you do not know whether or not your foil is well connected to the magnet mount itself, its best to just tear it off and redo the foil with copper tape.
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From a circuit analysis point of view (because I have never actually tried it), I would think adding those ground straps would make it worse, much worse.
Consider the self inductance of a single 1cm wide, .5mm thick strap that is 5cm long. Its self inductance is 28nH (Xl = 4.75Ω @ 27MHz). If you have to make that 5cm strap longer, the inductance goes up. At 15cm, it's self inductance is 116nH (Xl = 20Ω @ 27MHz). None of which are better than the 0.6Ω the capacitance offers by itself.
And even if you could get that reactance down, you are putting it in parallel with the capacitance of the mag mounts and the lower you go in inductor reactance (the shorter and neater you make those ground straps), the closer you get to where the straps and magnet capacitors are in parallel resonance at the operating frequency (and then you're really REALLY screwed).
I bet with three straps in parallel, you might get really close to the 0.6Ω of the capacitor. Then, you will have no ground at all!
If ground straps help a mag mount, it is because the foil is not electrically connected to the coax braid.
If ground straps help a mag mount, it is because the foil is not electrically connected to the coax braid.
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I have been doing this for decades, as have other engineers I know, that design and build HF mobile antennas for the commercial markets . The foil, or whatever it is, is not electrically connected to the mag. It's stuck on with adhesive. An electrical bond from the coax shield to the vehicle chassis, is nothing new.
Not arguing against it, just pointing out that with the foil connected, it can make things worse. As long as it works, thats what counts.
Mags at HF suck. I had so many heated discussions with a US antenna maker, about his low band mag mount sucking. He knew it sucked, but I told him he could do better. He sent me materials to build a better NMO low band mag mount (I still have a box of stuff from that project). His mag mount housing was too tall, which is really why it sucked for the most part. At the end of the day, the electrical bond wins over the capacitive coupling of a mag mount at HF.
The only reason mag mounts get a bad rep on 11m is because of lazy manufacturers who choose not to connect the foil (thats about 75% of them). If your first 3 mag mounts have had insulated foil, of course you will think they suck and ground wires are a must. However, I find it absolutely discouraging how I can break down the math and explain something just to have people that are totally unwilling to try argue about it. They have clearly never ran a mag mount with proper capacitive grounding. I'd put my mag mount up against anyones MacGyver grounding job because I understand how it works. Heck, Ive even used foil tape to couple an antenna base plate to the vehicle body without foil on the magnets, and it works amazingly well.
Back to the ground straps. Even without that magnet capacitance causing a parallel resonance (which would be a real issue at lower frequencies), say you tear the foil off completely and run only the ground straps, and lets further assume you dont care about the self-inductance of the straps, wherever they connect to ground, the path under the paint that goes back toward the base of the antenna just became a flat "sleeve balun" or hairpin that will act as some additional inductance (on top of the self-inductance) at the point the ground strap attaches to the antenna mount.
So, by all means, run your ground straps all over the place lol. Make hairpins out of your ground path, add tank circuits you never consider the resonance of, and above all else, make sure its ugly!
Back to the ground straps. Even without that magnet capacitance causing a parallel resonance (which would be a real issue at lower frequencies), say you tear the foil off completely and run only the ground straps, and lets further assume you dont care about the self-inductance of the straps, wherever they connect to ground, the path under the paint that goes back toward the base of the antenna just became a flat "sleeve balun" or hairpin that will act as some additional inductance (on top of the self-inductance) at the point the ground strap attaches to the antenna mount.
So, by all means, run your ground straps all over the place lol. Make hairpins out of your ground path, add tank circuits you never consider the resonance of, and above all else, make sure its ugly!
Just for fun, if anyone gets bored...
not sure why one link appears different, 2 links there
Flat Wire Inductor Calculator
chemandy.com
Capacitance of Parallel Plate Capacitor Calculator | Calculate Capacitance of Parallel Plate Capacitor
Capacitance of Parallel Plate Capacitor calculator uses Parallel Plate Capacitance = (Relative Permittivity*[Permitivity-vacuum]*Area of Plates)/Distance between Deflecting Plates to calculate the Parallel Plate Capacitance, Capacitance of Parallel Plate Capacitor formula is defined as a measure...
www.calculatoratoz.com
not sure why one link appears different, 2 links there
I have a Sirio 5000 antenna that came with the foil. For some reason I don’t recall, I changed the magnet with one without the foil. SER went up. I had to go back to the original magnet.
Definitely, the direct grounding is better but the foil works.
Definitely, the direct grounding is better but the foil works.