Screwdriver Antenna/40m, vs 9ft tank whip with radials on 40m

[rizz]

Heres a quick question, if you have a screwdriver antenna, the whip is maybe 6 or 7 ft the rest is the tunable coil, and I have seen them make contacts on 40m, now Im certain they are garbage on 40m but my 9 ft tank whip with 9ft radials, tunes on 40, so im thinking it must work as good as a screwdriver on 40m, not that i think a mobile whip works good on any band below 15m. I will get around to trying it but it makes me wonder how good the screwdriver is on 40m with such a small radiating element.

 

[DainBramage]

Heres a quick question...it must work as good as a screwdriver on 40m, not that i think a mobile whip works good on any band above 15m.....

perhaps because 40 meters is not above 15 meters.

 

[rizz]

perhaps because 40 meters is not above 15 meters.

Well spotted

 

[Captain Kilowatt]

Heres a quick question, if you have a screwdriver antenna, the whip is maybe 6 or 7 ft the rest is the tunable coil, and I have seen them make contacts on 40m, now Im certain they are garbage on 40m but my 9 ft tank whip with 9ft radials, tunes on 40, so im thinking it must work as good as a screwdriver on 40m, not that i think a mobile whip works good on any band below 15m. I will get around to trying it but it makes me wonder how good the screwdriver is on 40m with such a small radiating element.

Depends on how it is tuned. Is the tuner located directly at the base of the 9 foot antenna" If so then it will preform about the same as the screwdriver antenna. The idea of the screwdriver antenna is that the matching system is located directly at the antenna feedpoint and thus has VERY low loss and zero feedline loss after the tuner. If the tuner is located even a few feet from the antenna than under certain tuning conditions the feedline can appear as an almost dead short and shunt most of the signal to ground making an extremely inefficient antenna system.

 

[rizz]

Thanks for that reply Captain Kilowatt, I see your point, and my tuner is located 100ft away, on a plus note I worked a station today inter g around 150 miles away 5-5 signal which was better than I expected running 20 watts, I don't want to put my wire back up untill I move house so for the occasional contact on 40m it will do.

 

[Captain Kilowatt]

Thanks for that reply Captain Kilowatt, I see your point, and my tuner is located 100ft away, on a plus note I worked a station today inter g around 150 miles away 5-5 signal which was better than I expected running 20 watts, I don't want to put my wire back up untill I move house so for the occasional contact on 40m it will do.

I have been down the same road you are traveling at the moment. The SWR on your feedline will be extremely high and as such there will be a lot of loss. If you could remote mount that tuner at the antenna base there would be a big difference in efficiency. The antenna system here is in a state of change at the moment. Well state of pandemonium actually, and I just removed my only antenna in use. It was a doublet with legs about 60 feet long and fed with 450 ohm ladder line. The ladder line dropped down to the end of the house where I had a Yaesu FC-40 remote mounted auto tuner and the coax cable for about 50 feet into the shack. This allowed the coax to have a low SWR and hence low losses even though the SWR at the ladder line was high. Since ladder line can have low losses even with high SWR this was not a big deal. If I had fed this same antenna with coax cable all the way with a tuner in the shack it would not have performed nearly as good. Again, I have been down THAT road before too.

 

[Moleculo]

Don't forget that there are also a lot of different designs for the screwdriver antennas (especially coil design) which will also affect how efficient they can be on 40 meters and lower. Personally I'm a fan of the Hi-Q line of antennas (I have one). Add a cap hat above the coil and it becomes even more efficient. Of course it's not the same as a full sized dipole on a tower, but you can have a whole lot of fun with it - I do.