NVIS Info - Near Vertical Incidence Skywave Antennas

[K5UJ]

I wish you could do an A/B between the 100 foot high dipole and a ground mounted quarter wave vertical on 75.  My dream come true:  "Wow Rob, the dipole and vertical performed identically!  I could not tell which one I was on!   

But seriously, I hope the QRN doesn't dampen the testing tonight--doesn't look like a good night for the low bands out this way.

[k4kyv]

I haven't even had my receiver on for almost a week.  Just one thunderstorm after another, day and night. Forecast calls for possibly good condx Friday night, but I'll see what the lightning map shows before firing up.

Such is life out in the sticks.  No local AM activity.

[K5UJ]

Same here.  If the static crashes are 30 or 40 dB over 9, even a strong local carrier has a fight.  It takes around 20 minutes to hook everything up and get it all fired up and if I think I'm going to have to power it all down and undo everything in a few hours I don't even bother.  Tonight I'm reading my new issue of ER that arrived today.

[The Slab Bacon]

With all of this being said. Sometimes things seem to defy the rules.

My antenna system shouldn't work worth a damn, but everyone seems to hear me well and I always get favorable signal reports.

Maybe it's just the "Antennas by Eimac" factor...........................

[flintstone mop]

I erected the 75M coax-fed dipole at 48' high over the radial field and ran some tests from 4-5PM local time.

After A/B/C switching from the 48' dipole, 65' dipole and high loop array at 190',  I have some results.

With close-in locals, there is very little difference between the dipole at 48' and 65'. (The dipole at 65' has no radials under it)  I see maybe 1 db at best in favor of the low dipole.  The high loops are down maybe 15db as expected.

When listening to some stations in West Virginia (about 500 miles away) I see a big difference and the vertical take-off angles are doing their thing.  On the low 48' dipole, a particular W8 was S7.  On the dipole at 65' the W8 was S8. On the high loops, the W8 was S9+10.    

This series of tests showed that indeed, the lowest dipole has less lower angle than the dipole at 65', but the dipole at 65' STILL has a fair amount of high angle.

The best optimization would be to raise the 65' dipole to about 95' to fill in the gap between the lowest dipole and the high loops.  I'll bet that will show a big difference locally and make the lowest dipole a clear winner for locals less than  200 miles away.  

I will orient the dipole at 95' so that it better favors Washington state to the NW.  There is a lot of AM activity out that way.  Might even add a reflector behind it cuz there is really nothing to the east except for Africa.
 
Vertical take-off angles are the most important aspect of antenna optimization in the real whirl.

More results when I get them.

T

BTW, back to the article - We all know a flat dipole is better than an inverted vee for various reasons. According to their info, it costs 3db to lower the ends into a standard 45 degree angle inv vee.  Some power is absorbed closer to the ground while most is simply not radiated as much in the horizontal plane for NVIS. So, keep the dipole flat for local work.

Tom
Your tests are very informative. Not many Hams have the capability to string antennas up at various levels and give reports like this. Cuz this is the magic part of radio and the ionosphere.
Just like the SDR radio is to us SMUG folks. We can see what the hell is happening to the spectrum we are trying to use. The carriers, the QSO crowding into 'our space', etc etc.  When I can see waz happenin' I can make the appropriate adjustment and get back to 'arm-chair copy'.

thanks for taking the time, TOM VU
Fred

[W8EJO]

With all of this being said. Sometimes things seem to defy the rules.

My antenna system shouldn't work worth a damn, but everyone seems to hear me well and I always get favorable signal reports.

Frank,

RCA Ham Tips (Nov., 1952 - vol 12, No. 3) had a front page article on your antenna. See it here:
http://n4trb.com/AmateurRadio/RCA_Ham_Tips/rca_ham_tips.htm

The author touts it as a good NVIS ant. for 75 meters.

[Ralph W3GL]

   Terry,

   The spacing of the "Ham Tips" antenna is 12' vs 12" for Franks antenna.
    Mucho differenty  ...

[W8EJO]

   Terry,

   The spacing of the "Ham Tips" antenna is 12' vs 12" for Franks antenna.
    Mucho differenty  ...

Dimensions must not be critical.

[The Slab Bacon]

Dunno, but it works OK-Fine ? ? ? ? ? ?

[Steve - K4HX]

Hams have been using short antennas since day one. You really should not be surprised.

[The Slab Bacon]

Hams have been using short antennas since day one. You really should not be surprised.

You were the one who sent me the article that I got the idea from!!   

[Steve - K4HX]

Indeed. Some of that stuff was from a 1937 handbook. Buzzardly.

[WD8BIL]

Steve, are you saying hams have always ..... come up short?

[K1JJ]

Many AM'ers talk softly but carry a big schtick.

[k4kyv]

Hams have been using short antennas since day one. You really should not be surprised.

My 119' high 80m open-wire fed dipole works pretty well on 160m, but the bandwidth is extremely narrow.  Can't QSY more than ± 5 kc/s without readjusting the tuner.

I used it exclusively for a couple of years after the erection of the tower, before getting the radial system laid.

Profile can sometimes compensate for short.