Antenna height

[The DB]

DB I agree.

That said however, I've seen times when I my local buds were able to talk 200 miles, of a morning, into the San Antonino area and we all agreed...it was likely short skip...and higher angled lobes were working our signals higher into the sky.

The question is what is the cause of the "short skip" you are referring to. I could be wrong, but if it is early enough in the morning I would think it is more likely "ducting" than "short skip". Ducting does happen at upper HF frequencies, and is more than capable of contacts of such ranges at said frequencies, and would be more reliant on lower angled RF than higher angled RF. In the end I guess they would both have similar effects from the operators perspective...


The DB

 

[TheBlaster]

Marconi on 144MHz ? (2m band) And sorry you will have to clarify the where to where QTH bit how many miles would be handy info.. Well it won't be F2 layer skip that is for sure at VHF. And E layer... doubtful if he could make the contact any time.. cause E layer is FAR from reliable at any time of year never mind winter.

 

[TheBlaster]

"Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 25,000 feet (7,620 m). Such signals are thus directly affected by weather conditions extending over some hundreds of miles."

That is not the ionosphere that is basically warmer air bands in colder air, as mentioned adjacent to earth.

For balance it is not beyond the realms of possibility that some of higher angle radiation gets "trapped" in the duct before it goes higher up into the atmosphere, it really depends on where your duct is in relation to which lobe and distance from your QTH.. and we are all going to be guessing on that one on any given day.

200 miles is pretty much standard fare for tropo... we get that every few weeks in summer time over here on 11m band nets (assuming elevated stations at both ends 200-500m ASL)... regular contacts are 200 miles with ducting lifts. (even 250 miles reported)

 

[freecell]

DB, what type of ground is being used in these models?

 

[Marconi]

Ducting does happen at upper HF frequencies, and is more than capable of contacts of such ranges at said frequencies, and would be more reliant on lower angled RF than higher angled RF. In the end I guess they would both have similar effects from the operators perspective...

db, back it those days we knew nothing about this stuff, maybe just enough to be dangerous.

 

[Marconi]

Marconi on 144MHz ? (2m band) And sorry you will have to clarify the where to where QTH bit how many miles would be handy info.. Well it won't be F2 layer skip that is for sure at VHF. And E layer... doubtful if he could make the contact any time.. cause E layer is FAR from reliable at any time of year never mind winter.

Well Blaster, according to Google map Broken Bow is 333 miles away from Houston.

https://www.google.com/maps/dir/Bro...c3be4d8243!2m2!1d-95.4401304!2d29.8262044!3e0

 

[Captain Kilowatt]

....cause E layer is FAR from reliable at any time of year never mind winter.

Actually the E layer offers up some fine enhancements in winter usually around the end of December. It often allows 6m contacts at 50 MHz.

 

[Slowmover]

Well Blaster, according to Google map Broken Bow is 333 miles away from Houston.

https://www.google.com/maps/dir/Bro...c3be4d8243!2m2!1d-95.4401304!2d29.8262044!3e0

In my job that’s the distance between first and second breakfast.

.

 

[Road Squawker]

... being bent over the horizon by some weak ducting (of course we cannot know for sure where from where the RF enters the duct as we don't know where the duct is)...

There are real time maps available online to locate the E clouds.

I have never heard of the "negative gain" term either.


What many in this thread refer to as "short skip" is really DIRECT wave propagation.

 

[The DB]

DB, what type of ground is being used in these models?

Real (Sommerfeld-Norton), and I am using the default Average ground option in 4Nec2. I believe it was you I remember mentioning that you use EZ-Nec? This is one of the ground options that are the same across both versions of the Nec2 software.

I have a mast going from the radials of the antenna down to just above the earth as a direct connection to this type of earth in the model is pointless with this ground type. Instead I have chosen to use a capacitive ground system to capacitively couple the base of the mast to the earth below.

In addition to the radials that are a necessary part of these 1/4 wavelength antennas, I have a choke immediately below said radials, as well as a second choke 8.5 feet below that.

Hope this helps.


The DB

 

[Marconi]

Real (Sommerfeld-Norton), and I am using the default Average ground option in 4Nec2. I believe it was you I remember mentioning that you use EZ-Nec? This is one of the ground options that are the same across both versions of the Nec2 software.

I have a mast going from the radials of the antenna down to just above the earth as a direct connection to this type of earth in the model is pointless with this ground type. Instead I have chosen to use a capacitive ground system to capacitively couple the base of the mast to the earth below.

In addition to the radials that are a necessary part of these 1/4 wavelength antennas, I have a choke immediately below said radials, as well as a second choke 8.5 feet below that.

Hope this helps.


The DB

DB, I could tell your pattern was different and I remember you've used that setup before...but I could never figure it out.

In my real installs here, I typically placed my PU mast on some thick patio stone to keep the metal off the ground...which around here will eat the regular PU pole metal with gusto.

I never knew that might make some real difference, but I saw the results sometime with my models, if I isolated the mast from the ground about 3" inches. Typically the model improved.

I think I also found out that I could get closer, maybe 1/2" inches without the model producing an error warning, "the wires were too close."

Do you think that was what I managed to do back the, without knowing? It would be interesting to consider...if you can talk more about this capacitive coupling idea?

BTW, I use Eznec Ground Characteristic as Average: Pastporal, heavy clay Soil = 0.005 for Conductivity and 13 for Dielectric Constant on all of my models.

 

[Marconi]

In my job that’s the distance between first and second breakfast.

.

Slow, to be sure I don't know if 2 meters can talk that far or not, but that was what he use to tell me about his brother.

A while later Sanders called me an told me his brother had a HG CLR2 base antenna he'd give me if I would pick it up. I said, no way man am I going to Ok to pick up anything today or tomorrow. Then Sanders told me his brother lived right close by in his neighborhood. So, I got the antenna and it could have been all BS when I heard them talking on their radios. See how evil works in idle minds...I've likely told a story that makes me look foolish again.

Maybe them two old bastard got a laugh over making me look silly. I still see hams doing that even today, and I'm NO Ham.

 

[The DB]

As a direct ground connection is impossible with the Sommerfeld-Norton ground in Nec2, I have been experimenting with using an old idea as compensation, namely the capacitive ground. Essentially, I create a ground screen as close to the earth as I can in said program, using this ground screen as one side of a capacitor, while the earth below is the other side. You can't use just the tip of the mast above the earth as you described, there needs to be enough surface area which is why I use a screen. I am simply doing this as a workaround for the models to let me use the ground type I want to use over the least accurate and worst ground option of them all.

If you want to know more, dig out your .pdf of Cebik's "Counterpoise? On the Use and Abuse of a Word". What he was talking about from those old texts is what I am doing. No more, no less.

 

[Marconi]

Do you make this screen grid or is there a type of object in 4Nec2 that does that as a choice?

I see this feature.

 

[TheBlaster]

Actually the E layer offers up some fine enhancements in winter usually around the end of December. It often allows 6m contacts at 50 MHz.

Thanks C.Kilowatt... yes around winter solstice, but it is a much lower magnitude event than summer peak.

Nice one The DB.. I have a 1:1 choke balun as feed point on my GPA (although initial test was using just a S0-239 not a baanced antenna so not strictly necessary as I understand) I went for a 1:1 choke/balun as it made the feed point and antenna more robust and "belt and braces" for the CMC suppression. I have yet to test the balun version but it sits here next to me in readiness.

I guess you used a mast as the radials resonance will become blurred as they hit the ground.

Another spanner in the works with this antenna is that the radials are commonly bent to 43 degrees to match 50 Ohms (as is my own) and not left at 90 degrees to the radiating element. As I gather this also affects the radiation angle.

I have always had a fond place in my heart for the humble GPA.. simple as it gets and it works. It may not be a high gain mega blaster of an antenna but it is an effective antenna and looks great as well.

I would be very interested to see a "ground mount" model though when radials are bent 43 degrees feed point will likely be higher up depending on what band you are using the GPA for.