[SADXA] CORRECTION FT8s on 24916 @ 2147z

Wed Feb 6 02:07:20 EST 2019

Hi Tom, 

I was using an antenna simulator to generate an elevation plot for a 3
element yagi for 12m at 56 feet above ground. The plot shows graphically the
main lobe (and all other lobes) with the main lobe max gain at the 11 degree
angle. This main lobe angle will change with height of the antenna. 

The program allows one to interrogate the relative gain at any point on the
lobes. For example, it provided the difference in gain between the main lobe
at 11 degrees, and the gain at any lower angle, such as 3 degrees. 

At 3 degrees the power loss is 7.26 dB and at 2 degrees, the loss is about
-10 dB (a factor of 10 in radiated power loss to the 2 degree signal). 

If the maximum MUF (3000) is 25 MHz (3 degrees) and you are operating on 25
MHz, then you are losing 7.26dB of power at that angle on that frequency.
The power loss is going into space at the higher angles of your lobes. 

Lower angles will achieve higher MUF, but greater radiated power loss for
the signal. 

Yes, I agree, many may be unaware of how much radiated power loss there is,
when operating Ft8 at the MUF (3000) (or maximum upper limit frequency) for
DX. 

It surprised me after the analysis. 

We all tend to think that if we put the antenna up high enough and get the
elevation angel down to 8 degrees, that our main power is in that 8 degree
lobe. But the MUF being operated on may require the 2 degree elevation angle
instead, causing higher angle radiation, including the main lobe radiation,
to end up in space. 

I would think there would be a reference published somewhere showing the
radiated power loss relative to the main lobe at lower elevation angles (for
maximum MUF) as a function of antenna height. I did not find this in the
ARRL antenna book I have. 

As a result, one characteristic the FT8s have in common on the highest
possible frequency is their all weak signals, ideal for FT8!! 

73's Tom, and Good DX.

Bill W7EXG

-----Original Message-----
From: sadxa-bounces at mailman.qth.net [mailto:sadxa-bounces at mailman.qth.net]
On Behalf Of Thomas Kramer
Sent: Tuesday, February 05, 2019 11:28 AM
To: D Dismachek via SADXA
Subject: Re: [SADXA] CORRECTION FT8s on 24916 @ 2147z

Hello again Bill,
Not that it matters much but my LPA is at 501/2 feet. Hoe did you determine
the takeoff angle for my LPA? As an extra class I should probably know this
but can you give me a link or reference where I can learn more?  I think it
will surprise a lot of hams to know just how little RF gets to distant
places.  Thanks again for the info.  73 Tom
On 2/4/2019 10:17:33 PM, W7EXG (Bill) <w7exg at q.com> wrote:
Hi Tom,

Thanks for the info.

At 56 feet, your elevation angle was about 10 degrees.
Unfortunately, the MUF(3000km) (3 degree elevation angle) at our time was
22.6 MHz based on EGLIN AFB data, time corrected.

At 3 degrees, you main lobe power had decreased by 6.62dB, or by 78.22%.
This means at least 78% of your FT8 power is going into space. Your
elevation angle had to be lower in order for the MUF to increase to 25MHz
where some of your remaining 22% power was used.

I am not experienced with 80m DX. However, there are many in the club who
are, and have obtained their DXCC on 80m. I am sure they would be willing to
give you some pointers. I am just guessing, but one pointer might be -- you
need to get up early!! Hi Hi.

Best 73's
Bill W7EXG

-----Original Message-----
From: sadxa-bounces at mailman.qth.net [mailto:sadxa-bounces at mailman.qth.net]
On Behalf Of Thomas Kramer
Sent: Monday, February 04, 2019 4:19 PM
To: D Dismachek via SADXA
Subject: Re: [SADXA] CORRECTION FT8s on 24916 @ 2147z

Hi Bill,
First my power was ~100 watts and the antenna is indeed at just over
50ft (by 6") and is a Tennadyne T-11 log Periodic. You definitely have
mastered HF propagation. This is an interesting analysis. I'll have to
check out the site you mentioned.
Currently I am trying to chase my last 6 zones on 80m but missed a lot
of the winter season because I generally sleep in. Do you have any info on
that band? I have decode Zones 17,18, and 22 but no QSOs. 73 and thanks
for the info. Tom NQ7R

On 2/2/2019 9:02:02 PM, W7EXG (Bill) wrote:
Hey Tom,

FT8 ZP4KFX --2209z 24916 -- 1/2/19 UTC -- Way to go!! ~ 5200 miles!!

Thanks for coming up on freq., and the report.

I am studying the MUF of the FT8 signals, and there were no FT8s on 10m at
that time. Thus, I believe the FT8 MUF was somewhere between 25 and 28 MHz
at ~2200z.

A few min earlier, I heard several FT8s signals on 12m Freq., but not the
normal crowd as on the lower bands. This is why I raised the flag, as it
seemed CQ was being repeated, as there was no two back and forth going on.
So I think 12m was close to the top MUF.

What power and what antenna height were you using?

This contact is an example of the discussion I provided on Elevation Angle
vs MUF for FT8 signals.

At 2000z, 1/2/19 UTC EGLIN AFB reported fof2 of 6.43 MHz and a resulting MUF
(3000) of 22.6 MHz. This is an approximate Local Time value at EGLIN AFB.

When you made the ZP contact here in Tucson, (2200z), the earth just turned
under the EGLIN conditions and appeared in Tucson about 2 hours later when
you made your contact.

BUT you made your 1st hop at ~25 MHz.

So one might ask - what is the disconnect between the MUF 22.6 MHz (3000)
and the ~25 MHz you observed and made contact.

The MUF (3000) prediction is based on about a 3 degree elevation angle.

If your 12m antenna was at 50 feet, then the dominant radiation lobe was at
~11 degrees. Unfortunately, any 25 MHz signal with an elevation angle
greater than 3 degrees is going into space, since the MUF (3000) at ~3
degrees is only 22.5 MHz.

This suggests your elevation angle during contact was less than 3 degrees
resulting in a higher MUF of 25MHz, and a greater loss in radiated power
relative to 11 degree lobe.

A 2 degree elevation angle would have a power loss of about -10dB relative
to 11 degrees radiation. At 1 degree, your relative power would be reduced
to about -16dB relative to 11 degrees.

So you can see, the killer when operating FT8 at the highest MUF, is MOST of
your 25 MHz power is going into space. Only the
is="" being="">
used, and that is not very much.

Pretty crazy, but that is how FT8 seems to work at the highest MUF. That is
why there are no S9 signals anywhere at the highest FT8 MUF. 1500W on 12m
would have lost at least 1350W or more into space, for example, and I think
it may be much worse.

I find all this very interesting, as the highest FT8 MUF in fact showcases
the whole concept and value of the FT8 mode, especially for DX. Higher
signal elevation angles will simply lowers the MUF that can be used, and
reduces the radiated power loss relative to the main lobe.

Thanks again for your "special" FT8 Contact and report.

73's
Bill W7EXG

-----Original Message-----
From: sadxa-bounces at mailman.qth.net [mailto:sadxa-bounces at mailman.qth.net]
On Behalf Of Thomas Kramer
Sent: Saturday, February 02, 2019 3:09 PM
To: Tom Fagan via SADXA
Subject: Re: [SADXA] CORRECTION FT8s on 24916 @ 2147z

Worked him. He is wirking 6 & 7's
On 2/2/2019 2:55:30 PM, W7EXG (Bill) wrote:
CORRECTION FT8s on 24916 kHz

-----Original Message-----
From: W7EXG (Bill) [mailto:W7EXG at q.com]
Sent: Saturday, February 02, 2019 2:51 PM
To: 'Southern AZ DX Association E-Mail Reflector'
Subject: FT8s on 24116 @ 2147z

FT8s on 24116 at 2147z

If on CW, I could copy them.

MUF is currently this high for FT8s now.

Can anyone w FT8 work them?

73's

Bill W7EXG

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