[SADXA] Elevation Angle as it relates to FT8 - de W7EXG

W7EXG (Bill) W7EXG at q.com
Fri Feb 1 23:31:53 EST 2019 

Hi Eric, 

Wow - your right! I just looked at the Listing for the Ionogram Data-- and
it is EGLIN. No clue why I transposed?  I think EGLIN is pronounced EGGLIN??


You are still NEAR a large AFB!! Hopefully, you are farther away then 2km
from the Davis-Monthan runway? Hi Hi

I recall during the Vietnam War, the B52 Bombers flew right over the U of A
campus in the early 60s. It seemed like flights were every 15 min. or less.

These Planes were so loud; the Profs in my Engineering Classes had to
terminate their lecturing for awhile until the planes passed. The buildings
shook!!  

BTW I picked EGLIN AFB for Ionogram Data, as this AFB Latitude is N 30.5 deg
and Austin's latitude is N 30.4 deg. 

Since Tucson is about N 32.2 deg, whatever the propagation data is from
these two sites, this data will most likely be our data about 1 to 2 hours
later. Almost like having an ionogram sounding site in our back yard, unless
you just can't wait for the earth to turn. 

Here is a link to the EGLIN AFB Ionogram site.  If your interested, you will
note you can interrogate many propagation indices from 1999 to 2019, for
each month and for each day and for each 15m time interval of the day in
UTC. 

 https://lgdc.uml.edu/common/DIDBYearListForStation?ursiCode=EG931

There are 117 such sites all over the world. 

There is much great propagation data provided by these ionograms, namely
fmin (lowest reflected frequency - varies with high D absoprtion), foF2,
foE, MUF vs Distance (actually varying elevation angle as discussed in my
presentation producing different M factors), M factor for MUF(3000km), hmF2,
and hmE (Layer heights of F2 and E layers) and there is also foES (Critical
frequency of Sporadic E).. etc. 

This is all raw data at a specific time; no fancy graphing over time. 

This type data allowed my formulation of the EMUF daytime boundary that
defined the 40m DX DAY propagation corridor I discussed. 

Thanks for bringing the EGLIN error to my attention, Eric. 

73's
Bill W7EXG

-----Original Message-----
From: sadxa-bounces at mailman.qth.net [mailto:sadxa-bounces at mailman.qth.net]
On Behalf Of Eric Gustafson
Sent: Friday, February 01, 2019 5:21 PM
To: Southern AZ DX Association E-Mail Reflector
Subject: Re: [SADXA] Elevation Angle as it relates to FT8 - de W7EXG

Just one small nit to pick Bill.

It is Eglin AFB not Elgin AFB.  I used to live about 2KM off the west end of
the SAc runway there.

73,  Eric  N7CL


-----Original Message-----
>From: "W7EXG (Bill)" <W7EXG at q.com>
>Sent: Jan 30, 2019 10:10 PM
>To: 'Southern AZ DX Association E-Mail Reflector' <sadxa at mailman.qth.net>
>Subject: [SADXA] Elevation Angle as it relates to FT8  - de W7EXG
>
>SUBJECT: Elevation Angle as it relates to FT8 
>From: Bill W7EXG
>
>During my presentation on 40m DX DAY Propagation Corridor, I made a point
>regarding that a 40m Dipole/Yagi at 0.55 wavelength height, or a Vertical
or
>a 4 Sq. antenna, the elevation angle is around 23 degrees (+/-).  This
>elevation angle is simply the angle at which there is a maximum of RF
energy
>density from your antenna.  Of course, there is much radiation above and
>below this 23 degree angle. 
>
>I would like to point out that the greatly reduced RF energy at greatly
>reduced lower elevation angles is likely most often being used by FT8 mode,
>and not by CW or SSB modes.  I am sure most of you are aware that for a
>fixed antenna height, the power radiated density degrades with lower
>elevation angle, and most of you are aware that low elevation angles yield
>higher MUF and longer DX. 
>
>But I think the table below, makes an interesting point you may not have
>thought of regarding FT8, when these two effects are combined. 
>
>Anyone with an Antenna Simulation program and access to the Digital
Ionogram
>Data base (online free) can generate the following illustrative tables
>below.
>
>DAYTIME 
>
>Currently (1/30/19) the Elgin AFB (30.4 deg Lat) Data base is showing peak
>foF2 (Critical Frequency for the F2 layer) of about 5.3 MHz at their solar
>noon.  
>
>Assume, as reference, ANY signal with an elevation angle of 27 deg into the
>F2 region, running 100W at that time and space. 
>
>Below is a table of signal strength vs elevation angle vs MUF = M (foF2).
>[The M factor was discussed for E layer, but a similar graphic can be
>generated for M factor of the F2 layer]. 
>
>DAY TABLE
>ELE ANG(deg)      REF(dB)   PWR(W)  MUF(MHz)
>
>27			0 dB	  100		10.4
>13			-3	   50		16.1
>8.5			-6	   25		18.5
>5			-10	   10		20.3
>1.5 			-20	    1		21.4
>
>What this table shows, is station running 100W on a 15m antenna (1/2 wave
>height) (21.075 MHz) will be acting as a QRP rig, running instead 1 Watt on
>15m (21.075 MHz). The higher Angle 15m RF power with lower MUF will be
going
>into space. Your 15m KW is radiating 10W of reflected power on 15m. 
>
>Today, (1/30) I listened to 15m FT8 frequency 21075 kHz about our solar
noon
>period, and heard many weak FT8 signals. (I did not hear can CW or SSB
>signals) I must also point out that I did NOT hear any 12m FT8 signal 24916
>kHz at that time or the remainder of the day.  Thus I am confident the MUF
>limit (for 1.5 deg angle of radiation) was between these frequencies. 
>
>NIGHT
>Currently (1/30/19) the Elgin AFB (30.4 deg Lat) Data base is showing foF2
>(Critical Frequency for the F2 layer) of about 3.2 MHz at around 2am local
>Elgin time. 
>
>Assume as reference ANY signal, with an elevation angle of 27 deg into the
>F2 region, running 100W. 
>
>NIGHT TABLE
>ELE ANG(deg)      REF(dB)   PWR(W)  MUF(MHz)
>
>27			0 dB	  100		6.1
>13			-3	   50		8.9
>8.5			-6	   25		10.0
>5			-10	   10		10.7
>1.5 			-20	    1		11.19
>
>What this table shows, is station running 100W on a 30m antenna (1/2 wave
>height) (10.136 MHz) will be acting as a QRP rig, running instead from 1 to
>10 Watts on 30m. The higher Angle 30m RF power with lower MUF will be going
>into space. 
>
>I recently listened to 30m FT8 frequency 10136 kHz and could heard weak FT8
>signals throughout the night.  I must also point out that I did NOT hear
any
>20m signal 14076 kHz at that time or the remainder of the night. 
>
>SO WHAT DOES THIS ALL MEAN?
>
>These Tables clearly show:
>A)	Low angle RF has perhaps > 20dB attenuation from the main lobe, and
>is more like a QRP signal. (To get 1W of reflected power at 1.5 deg, you
>need 100W)
>B)	This low RF power with low angle of radiation has a much higher MUF.
>C)	This results in very weak signals at much higher frequencies. When
>you tune and find the highest frequency FT8 signals, they are generally
>weak. They are likely coming effectively from a 1W to low wattages sources.

>D)	If you call CQ on CW with 100W under these same conditions, your
>effective 1W CW signal might be heard, but not copy-able, or ignored. 
>E)	The main lobe RF had a lower MUF, and went out into space. Most of
>the lobe also whet to space, since having a lower MUF.  In some cases, only
>about 1% of the power was actually reflected at 1.5 deg.   
>F)	FT8 Technology is a weak signal decoder based on low bit rate
>transmissions. It is well suited for receiving weak signals emanating from
>1.5 deg elevation radiation at the highest possible MUF. 
>
>LESSONS LEARNED: If you hear a weak FT8 SIGNAL on an otherwise dead Higher
>Frequency band, FIRE UP YOUR LEGAL LIMIT LINEAR AMP AND CALL CQ (CW/SSB) ON
>THAT BAND. YOU MIGHT ONLY BE REFLECTING 15 WATTS, BUT hey, SOMEBODY WILL
>HEAR YOU and MIGHT RESPOND. You might need to ask them to QRO!! 
>
>73's
>Bill W7EXG
>
>
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