The 5/8 and .64 debate!

[Toll_Free]

Chollas Heights

That's it! That view shows Lake Chollas in the foreground.


Sadly, it's all gone. Google earth Transmitter Rd. in 92116 zip... Sad, it's all gone, all military housing.

35 on the border has a piece of coax from it, though.


--Toll_Free

 

[1200RI]

http://www.oldradio.com/archives/stations/cinc/wlwpix.htm Here is a big old radio station 500,000watts!

 

[Hamin' X]

Great article.

Rich

 

[viking63]

I'll do you one better! I'll change the title AND make it a sticky! I'm all for the discussion, I learn more everyday!

In the beginning, there was CDX-007!.....



Then came.....



Followed by a blantant HYJACK.....



Then back to 007.....



Then me again.....



007.....



me..... (I'm almost caught up)



Then C2!



and finally, Corn Hollio.....

hello, as i've read from one or more post here. "that an antenna that isn't a resonate of 1/4 wave of the frequency, it wont work." then why do so many 5/8th wave work. doing it better than a half wave antenna. we all know the longer the tuned radiator is the stronger the received signal. especially when it comes to a shortened antenna. now i've been wanting to run 4 half wave antennas, in a collinear design with phasing cables. then if that works, there would be no debate.

 

[wavrider]

hello, as i've read from one or more post here. "that an antenna that isn't a resonate of 1/4 wave of the frequency, it wont work." then why do so many 5/8th wave work. doing it better than a half wave antenna. we all know the longer the tuned radiator is the stronger the received signal. especially when it comes to a shortened antenna. now i've been wanting to run 4 half wave antennas, in a collinear design with phasing cables. then if that works, there would be no debate.

Have at it, document your results ,come back and post your findings

 

[M0GVZ]

hello, as i've read from one or more post here. "that an antenna that isn't a resonate of 1/4 wave of the frequency, it wont work." then why do so many 5/8th wave work. doing it better than a half wave antenna. we all know the longer the tuned radiator is the stronger the received signal. especially when it comes to a shortened antenna. now i've been wanting to run 4 half wave antennas, in a collinear design with phasing cables. then if that works, there would be no debate.

It all depends on where the signals are coming from. There's this thing called the angle of arrival. Depending where you are on the planet and where the signals are coming from, they will arrive mostly at certain angles. Rule of thumb is the closer they are the higher the angle of arrival. Up to a couple of thousand miles or so the angle will be quite mostly from 12-15 degrees. 3000-6000 miles they'll be 7-11 degrees, 9000-12000 miles they'll be mostly 1-5 degrees.

So why does this matter? Well the more over a half wave you get, the more a lobe is created in the elevation pattern at a high angle. The further you get away from the halfwave the stronger the lobe is until the lobe has more gain than the low angle gain we want. At 15-45 degrees a halfwave has a null. At 30 degrees a 5/8 wave has a lobe. So on a 5/8 wave any signals from hundreds of miles arriving at an angle of around 25-45 degrees would appear to be stronger. We therefore assume the antenna is working better. With a .64 wave the lobe is even stronger so again basing it on the "DX" we hear from 100s of miles its working even better. And indeed it is for stations at that distance with signals arriving at those angles.

But...below that lobe is a deep null before we get the lobe we want for real DX, the one from 0-10 degrees. If you've a station with a signal arriving from say 1000 miles at say 20 degrees it could be the case that because that's still in the lobe of a 1/4 wave but in the null of a 0.64 wave that the 1/4 wave receives it far stronger than the 0.64 wave.

Longer does not always mean better. In the case of a doublet, because the pattern can be so bad a we get above a full wave with some really deep nulls, the station you want could end up being in the direction of one of those -30dB nulls meaning your 2 wavelength long dipole is working worse than a half wavelength one.

 

[Needle Bender]

Hey Marconi,

I'd like to see patterns of both:
a horizontal 1/4 wave radial fitted .625 (ie: P500 / I-10K)
&
a horizontal 1/4 wave radial fitted .64, (6.5" longer than the 22' 6" .625)
EACH at:

1) 72' at the radials,

2) 72' to the bottom of the top 1/2 wave (radials at 67.5')

3) 72' at the high current node, 1/4 wave down from the top, (radials at 58.5').

I plan to install one this coming weekend at the best of these 3 heights - according to how your graphic patterns look.

- If you have the time & energy that is.
73

 

[The DB]

As I haven't seen Eddie post in three months or so I took this up.

Model reference info:

I used a different ground type than normal, I used the "rocky, steep hills" option as if memory serves it is closer to the terrain where you live. I'm not sure on your specific ground conditions, if there is a better ground option to use let me know and I can update and rerun the models.

I used T6 aluminum for the antenna elements (vertical/radials).

I used standard L networks tuned to optimal for these antennas. Again, I am not sure of the Q and loss data for the matching network you are going to use for said antennas, so I used sad L-networks as more or less a generic stand in.

I also have a wire attached from the base of the different antenna models running to ground. The lower antenna heights showed slightly more currents on this wire than the higher antenna heights, but none of the models here had significant currents on this wire. The radial system seems to be doing the job of isolating currents admirably.

OK, 72' to the radials...

67.5' to the radials...

And 58.5' to the radials

NOTE: Two of these heights the .625 wavelength antenna has slightly more gain than the .64 walvelength height. While some people will see this as surprising, this is not the first time I've seen this happen in models. In past experiments with modeling I have noted a different gain curve for .625 and .64 wavelength antennas as you elevate them above an earth. Further, different grounds also affect these curves as well. These height/ground conditions seem to add up to one of the areas the curves cross.

Continuing the note with a past observation, informational purposes only. In some height/ground type conditions I have found the optimal length for low angle gain is less than .625 wavelengths, and in others it is greater than .64 wavelengths. I didn't try every possible length for said heights in the models above, only the two listed that you said you wanted.

Hope this helps...


The DB

 

[Needle Bender]

Awesome effort DB, Many thanx@!! Sorry to hear Eddie has been AWOL, I hope he's doing well.
No, this will be in flat, boring prairie-like dryness.

I recall when he did some graphs a year or five ago his showed a much larger bump, (maybe .7-.9db?) in .64 gain over .625 around 20°-30° but yours doesn't show that, odd.

Maybe I'll just get an A99 and toss it up there 180' lol

I'd like to go into this more, but I'm being beckoned, gotta go- Back later

 

[Needle Bender]

Hey DB, would you like to add a graph for a vertical 1/2 wave (like a Starduster) with it's center at the 58.5' level? (same mast height as the lowest .625 graph)
Might be interesting to see the difference in the nulls, especially at 52°.

 

[The DB]

Hey DB, would you like to add a graph for a vertical 1/2 wave (like a Starduster) with it's center at the 58.5' level? (same mast height as the lowest .625 graph)
Might be interesting to see the difference in the nulls, especially at 52°.

When I get some time later I'll make it up for you, might be tomorrow though depending on how my day goes...

Do you want the 10 inch "radials" mounted about half way up the upper element included or no?

I also intend to modify the ground in the models above to better match the prairie conditions you mentioned above... I don't think there will be much of a change, the ground data is very similar I think, but we won't know for sure until it is done...


The DB

 

[Needle Bender]

Thanks DB, and no need for the mini-radials, I believe they're just for aesthetics anyway.
Maybe better a full-size end-fed 1/2 wave like the Proton99. Nice & straight that way.

 

[M0GVZ]

Thanks DB, and no need for the mini-radials, I believe they're just for aesthetics anyway.

If they're on the radiating element they act as a capacity hat and move the RF current maximum up the antenna as well as allow the antenna to appear electrically longer so they do actually do something unlike those mickey mouse 4 inch ground plane things at the bottom of the antenna.

 

[Needle Bender]

If they're on the radiating element they act as a capacity hat and move the RF current maximum up the antenna as well as allow the antenna to appear electrically longer so they do actually do something unlike those mickey mouse 4 inch ground plane things at the bottom of the antenna.

We were referring to the Starduster, a center fed 1/2 wave dipole with no coil which, to the best of my knowledge, would be required to raise the current in a somewhat shortened (capacitively reactive) radiator.
I'm not aware the mini radials actually do anything except look interesting.
And I don't see why one would want to interrupt a smooth 1/2 wave bubble of current if the antenna is not in need of a coil nor matching device, as it is already a 50Ω direct-fed vertical 1/2 wave, but I guess you'd have to ask 55.

 

[Marconi]

Hey DB, would you like to add a graph for a vertical 1/2 wave (like a Starduster) with it's center at the 58.5' level? (same mast height as the lowest .625 graph)
Might be interesting to see the difference in the nulls, especially at 52°.

NB, here is my model of a Starduster to specs, at 64' feet to the hub, and no cap hat. Title of model is (Sd'r Best 021915 64')

The model is over Average real Earth. I have also added to the attachment the model with currents turned on and off...for your consideration.

IMO this SD'r model produces an improved pattern at low angles for communications. I note that the SD also produces an effective 17.3* degree Beamwidth pattern, at the lowest angle of radiation, as compared to my 5/8 wave antenna models at or near similar heights above Earth showing a beamwidth near 7* degrees.