Which is more efficient?

[Moleculo]

I was recently have a conversation on the air with a local ham and we starting talking about mobile HF antenna systems. He asked me a question that I didn't really know how to answer, so I figured I'd post it here:

Power handling capabilities aside, which is a more effective system: a mobile screwdriver HF antenna, or a straight antenna of the same height as the screwdriver except used with an antenna tuner (no screwdriver tuning)?

My immediate reaction was that the screwdriver design would be better because the current stays constant from the base through the coil and the coil can also help mitigate ground loss, but I honestly have not been able to come across a definitive answer to this.

Anyone?

 

[Moleculo]

Noone wants to take a shot at this?

 

[W5LZ]

Mole',
A loaded antenna is normally more 'effective' than an unloaded one when their lengths are less than a 'resonant' length.
- 'Doc

PS - That's 'effective', not 'efficient'! Depending on length/freq. usage, efficiency can be quite low and it still be 'effective'. Glad you said 'effective' - lol...

 

[Moleculo]

OK, so my initial reaction was that the straight antenna with a tuner would probably be slightly less effective (or at least equal) to a base loaded antenna of the same length and resonance. Does that sound like a reasonable comparison?

 

[W5LZ]

Mole',
I'm not sure I would say 'equal' to a base loaded antenna. Just depends on how the whole thing was set up I guess. Base loaded antennas are not exactly the 'best', but they certainly beat some other things I've seen used for antennas.
Have a friend who tried an SGC tuner and whip thingy on 80 meters. NOT even close to what you'd call effective, compared to almost anything else! LOL, then he tried the same thing with a loaded antenna instead of the whip. Not exactly the best in the world either, but certainly better than before. It depends on just how small a fraction of a wave length the whip is, so 80 meters would be an extreme example of the whole mess. Hows that for confusing the original question?
- 'Doc

 

[Moleculo]

Well, actually 80m is a good example, since that's the worse case scenario. Because of the example, it gives some meaning to the discussion. Makes perfect sense to me.. LOL

 

[Master Chief]

Just saw this post. The screwdriver antenna is better than the Francis Amazer with the AH-4.....although that package works real well!

 

[rfoverlord]

but on 80mtrs. they all are lousy, but work. so which would be the better of the 2, a 8.5 ft whip & tuner or the screwdriver ant.?

 

[Moleculo]

I think we all agree that the Screwdriver would work better.

 

[W5LZ]

Of those two choices, the screwdriver would be 'best', I would think. But for 80 meters, or any single band below 40 meters (give or take a bit), a fixed tune/non-adjustable antenna that's long and has a large diameter loading coil will produce the best results. Or, a large diameter loading coil on a screwdriver would work 'best'. (Not that there's anything wrong with the 'ordinary' screwdriver, but the lower the frequency the bigger the coil, seems to be the 'best' bet.)
I had a home-brew screwdriver but thanged back to the BugCatcher. Biggest problem was mounting the @#$ thing on my car, not to mention matching the thing with more than 100 watts output (got hot). The BugCatcher doesn't get hot, just tends to snap the typicl Radio Shack ball mounts after about 4-5 months. Oh well, if I wasn't so cheap I wouldn't have to keep replacing mounts...
- 'Doc

PS - Got the DSL line working again! The last 7-8 days have been terrible with internet withdrawal...

 

[rfoverlord]

okay, now i will stir the pot a little so the bottom doesn't get burnt. out of the screwdriver types out there today which is the the most efficent? (and yes i have seen e-ham) the only reason i'm asking is that i know very little about them, and the reviews for the most part all say how great they are, but which design would be the best all around? sorry if i'm kinda stealin this thread.

 

[C W Morse]

o

All around, your best bet for an HF mobile antenna is the screwdriver. The 3" screwdriver units REALLY get the job done!
For single band, the center-loaded Bug Catcher will usually whip all comers. There's a link on the page for Carolina Cyclone screwdriver antennas and if you will email me, I'll send you a couple of pictures of my pickup truck with the screwdriver mounted. If you pick the right screwdriver, you will have no problems with power-handling; just stay away from PVC loading coils. Many of them will (including CC will handle full legal limit SSB)

A good rule of thumb to follow is that it takes a BIG, UGLY (well, not THAT ugly) antenna to work the lower bands (40 and 80 Meters). Your tuner/whip combo will work fairly well above 40 Meters, but you sacrifice performance for convenience.

Hope this helps.

73

CWM

 

[rfoverlord]

appreciate that quick response, next question what will hold up to the winters here in the upper mid west?

 

[C W Morse]

Most of the screwdriver antennas will hold up. About the only thing I ever run into is the clear covers either crack and split and/or the beauty caps will fade IF you don't paint 'em from time to time. Mine are 1/8" wall Lexan OR thin-wall PVC (not to be confused with the loading coil material which is Nylon). Like any machine, a screwdriver is a mechanical device as well as an electrical one. The key is to do a little maintenance about once a year by disassembling it and oiling the internals. There is little to go wrong with them since the "innards" are protected inside the mast away from water and dirt. However, dust CAN filter up inside and a little oiling and cleaning goes a long way.

With my antennas, one of the things I have done is to do away with "fingerstock" per se. the contact is brass and is secured to the contact pad with a spring that holds this contact surface tightly to the coil to keep electrical contact at all times. Some builders use a spring to serve as the electrical contact itself, but this seems to wear out the coil windings faster and must be replaced about once a year. Mine simply acts as a "slide" and the spring holds the brass contact surface securely.

I like the "F" mount that slides into the ends of Reese hitches because it allows for mounting AND supporting the antenna as a unit. If you can imagine an "F" turned upside down and the center cross bar turned to the OUTSIDE (see the "Carolina Cyclone" ad for address. These mounts can be found at many antenna outlets.

Anyway, take a look, and if you will send me a line, I will send you some pics that show the mounting.

73

CWM

 

[W5LZ]

C W Morse,
Already solved the mounting problem, got rid of the #$% car! I find that mounting a big antenna on a pickup is a whole lot less demanding, much simpler, more places to weld to (except for the 'plastic' bumpers)...
- 'Doc