The AM Forum

This afternoon just before 75 died I was listening on 75 to a bunch of guys including W1IA. He flipped the phase on his antenna and I was shocked.
I only wish my SDR set up was turned on to get an accurate DB reading but it was well over 10 dB. I never tried the 135 degree delay line but I see by simulation the reason he went that way.....very cool!

I have been running an array here for over four years. I wouldn't trade it for anything that would fit in my yard. It takes just a little more room than a half wave dipole!

They are extremely simple antenna's.  ON4UN's Low Band DXing has full documentation and systems if you are interested so you won't have to re-invent the wheel.

I am using two dipoles 1/4 wave spacing. It has enhanced my listening capabilities and in my opinion that is the greatest advantage, being able to shut down unwanted noise in the receiver. I have had reports averaging 15 - 18 db  over the last three years!  You have to love it.

Frank you are very close in to  Brent so I would guess you are seeing more of the vertical components than the true long haul effects.

Those Short Wave B'casters know that they are doing after all............hi
It's always a money or real estate thing for us pow folk

Fred

Gary,
I had a pair in the woods about 10 years ago when a tree ripped one dipole down. I've collected all the parts to build another and looking at 3 element. It will also fit in my back yard between the tower and tree line. I miss the performance. i've had the bug ever since Brent mentioned it. 

Still testing, but after additional modeling with the feedlines we ended up at 90 degree delay.
The feedlines play a huge part in the model. I experimented with 70, 90 and 125. It came back to 90 degrees. Final numbers are 9.51 dBi gain with 15 dB front/back. Take-off angle is 45 degrees. It is amazing on the air; I agree with Gary...I am spoiled instantly.

Advice...stick with 1/2 wave feedline lengths. Antennas cut for 3.8 mhz. All feeders are tuned 1/2 waves at 3.8 mHz. I have 3 half-waves total into the shack and made for easier feedpoint impedances. Much smoother resistive component. Mark KA2QFX and I have been working on this system for 2 months now and will publish all the info soon.

In a nutshell: Antenna cannot be lower than 55 ft (model falls apart) Maintain 55 feet spacing. Use 1/2 wave multiples of feedline. Measure, measure , measure you cannot do this without an analyzer (MFJ or other) Tuning feedlines, antennas, stubs etc. If you don't hae an analyzer use the free TLD software by ac6la. This is dead on and you can calculate your feeders without an analyzer and be almost perfect.

Stayed tuned for addtional data....p.s. I have 1 uh of series inductance 500 pf shunt and add 500 pf more to move the antenna up to 3885 khz....Antennna cover from 3.5 to 3.93

Brent W1IA

http://amfone.net/ECSound/K1JJ21.htm

I knew I read this from K1JJ some time ago

I first heard Brent using the new set up a coupla weeks back when the band was out. The only way I could tell it worked was that I could only hear him on his dipole.  ;D

10db is the general/typical difference seen here. Depending on band conditions, I've seen 15 or more from G, perhaps due to the increased distance. But what an incredible tool to have at your disposal for a very limited amount of money and time invested. Well, okay - maybe just the money part.

Yet another reason to move to a place with some usable real estate! 

I'm simulating at 60 feet and also playing with a third element. I have the wire and a fresh spool of coax. And the fancy center insulators with cable clamps. I do notice things change with delay. What antenna length did you end up with? I think my old set up was around 122 Feet. I'm looking at 1/8 wave spacing for three elements.
Tower end will be agout 65 feet and tree end about 75 feet or so depending on where the rope catches a strong branch.  i ran 90 degrees before and yes 1/2 wave length feed line or a tad longer is what I did. fc

Elements were 123 feet per dipole center fed. Send me the model if you can.

Brent W1IA

I was about 2 half waves in the old set up With all splitting and delay  Switching inside the shack. Looks like the spool I  have has about 250 feet on it which should be enough for new set up. New set up will be closer to SW/NE broad side. I am looking at drooping the ends so need to try Dipoles to see how they compare. I do notice things go crazy near the ground. Found that with the 4 element LPDA. It is 4 inverted Vees but if ends get closer than about 20 feet to the ground it blows out. I only have  tall sopports in the back yard on one side then the tower is on the east side so need to look at ropes to small trees on the side of the house.

The FB you see depends on the path. As you can see below, as some angles, the FB could be very high and other its nil.

I saw the same thing in my simulation. I must have been in a deep high angle null off the back side. I only wish I had the sdr set up turned on so I could accuratly measure the F:B. I saw 20 db on the Racal but it is just a bar display with 10 dB per bar.
I'm sure getting the bug to get my set up going again.

After a lot of thought I remembered I never worked JA's on 75 with the phased dipoles only the 160 meter dipole......
Now I'm looking at a 3 element close spaced thing This would simulate a log cell with 3 feed lines so the pattern can be reversed. I'm looking at 185 or 190 degree phase shift between elements. I need to compare it to low angle radiation coming off the dipoles but I do see gain at 15 degrees. F:B at 3.75 MHz is over 20 dB at 30 degrees. Spacing is presently 16 feet between elements. all three elements the same length around 122 to 123 feet total
Simulating antennas here in the solar room at 80 degrees is a lot easier than cut and try outside at 30.