OK, after the thread on PL-259 losses, I figured
my system (ant gain - connector losses - coax loss)

150 mhz total net gain 1.006 DBi
450 mhz total net gain 2.797 DBi
Antenna tip is 32'6" above ground

My proposed system would replace the RG 58 coax pieces
with a single section of Flexi 4XL and the antenna would
be a Comet GP-9. The new figures a

150 mhz total net gain 7.919 DBi
450 mhz total net gain 10.553 DBi
Antenna tip is 47'6" above ground

150 mhz = 6.913 db improvement
450 mhz = 7.756 db improvement
Antenna tip 15 feet higher

Cost - about $250 for the improvement.

Now here's my question - will I notice the improvement
enough? I've had several OM's tell me that on SSB, CW
or HF I would but not on 2m/440 simplex and repeaters.


Ken KG0WX

Now here's my question - will I notice the improvement
enough? I've had several OM's tell me that on SSB, CW
or HF I would but not on 2m/440 simplex and repeaters.

Well, a 6 dB boost would double your range, IF you aren't hitting the limits
imposed by your radio horizon. VHF and UHF don't "bend" much, so once you go
beyond your radio horizon, you're pretty much done, no matter how much
signal you had. It will improve your signal into repeaters, where you were
a little noisy before, you should be quiet. On simplex, you'll notice
better signal once you get far enough away that you used to be no longer
full quieting.

In an FM receiver, there is a signal limiter, that caps the signal level, so
if you were already "full quieting", then no amount of power increase would
result in a better signal. If you are far enough away that you're not full
quieting, then yes 6dB will be noticeable.


--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR

Well, a 6 dB boost would double your range, IF you aren't
hitting the limits imposed by your radio horizon.
_____________

Clarification: the coverage AREA doubles for the above situation, but the
"range," or distance from the transmit antenna to a given field strength
value increases only by about 40%.

Here are the numbers, using the FCC's F50,50 curves for UHF NTSC TV
propagation.

50W ERP from 100 feet above average terrain:

60dBuV/m at 2.99 miles
Coverage area within the 60dBuV/m contour = 28 sq miles

200W ERP from 100 feet above average terrain (a 6dB ERP increase from the
above example):

66dBuV/m at 2.99 miles
60dBuV/m at 4.2 miles
Coverage area within the 60dBuV/m contour = 55.4 sq miles

The radio horizon for these examples is located about 14 miles from the
antenna site (at a 0.15 degree depression angle).

RF

Visit http://rfry.org for FM transmission system papers.

From: "Richard Fry"
Date: 11/9/04 6:29 AM Pacific Standard Time
Message-id:

Well, a 6 dB boost would double your range, IF you aren't
hitting the limits imposed by your radio horizon.
_____________

Clarification: the coverage AREA doubles for the above situation, but the
"range," or distance from the transmit antenna to a given field strength
value increases only by about 40%.

Here are the numbers, using the FCC's F50,50 curves for UHF NTSC TV
propagation.

50W ERP from 100 feet above average terrain:

60dBuV/m at 2.99 miles
Coverage area within the 60dBuV/m contour = 28 sq miles

200W ERP from 100 feet above average terrain (a 6dB ERP increase from the
above example):

66dBuV/m at 2.99 miles
60dBuV/m at 4.2 miles
Coverage area within the 60dBuV/m contour = 55.4 sq miles

The radio horizon for these examples is located about 14 miles from the
antenna site (at a 0.15 degree depression angle).

RF

Visit http://rfry.org for FM transmission system papers.

I stand by my statement, " 6dB doubles your range". Rather than going to an
obscure site and referencing something about some TV coverage - just run the
numbers. We are not talking about broadcast to consumer TV sets here. Anyone
who has done path analysis knows that 6dB doubles the range. Check into it -
you might learn. On second thought here is the equation -
Loss (dB) = 36.6 + 20 log F (MHz) + 20 log D (statue miles). And, again, as
first stated, " within the limits of the radio horizon". Off course, space
shuttle mobil and EME folks don't worry about the horizon.

KF6HHS
Retired, now life moves at my pace.
please note spam filter

"KF6HHS" wrote:
I stand by my statement, " 6dB doubles your range...
Anyone who has done path analysis knows that
6dB doubles the range. Check into it - you might learn.
_____________

I've checked, thanks.

The field strength values I posted are based on empirical data used by the
FCC to determine coverage range, and protection ratios for FM & TV broadcast
stations. The same physics applies to "hams" as to broadcasters.

The free-space path loss formula over a reflection-free path gives different
results. But, as the original post asks " Is it worth it? Will I notice?,"
the real-world values from the FCC curves will give more applicable answers.

Verify my numbers and conclusions for yourself at
http://www.fcc.gov/mb/audio/includes/curves.html .

You might learn g.

RF

KF6HHS wrote:
"I stand by my statement: 6 dB doubles your range."

The "Sommerfeld formula" is ancient and accepted. It says:
Ground-wave field strength = (A) Eo / d
Eo = field strength at the surface of the earth at a unit distance from
the transmitting antenna, neglecting earth`s losses
d = distance to the transmitting antenna
A = factor taking into account ground losses

If the earth is perfect, the above reduces to:
volts/meter = Eo / d
assuming the right scale factors.

At twice the distance, the field strength over flat earth is halved.

The resulting current is also halved. Thus, the power, their product, is
quartered. That`s a 6dB change from doubling the distance.

On the other hand, if you want to produce the same field strength at
twice the distance, you must use 4X the power by the Sommerfeld formula.

Best regards, Richard Harrison, KB5WZI

A long time ago, when there was not so much man-made noise, I found that in
the almost-flat-country at the extreme edges of coverage from a base station
to a mobile station, the rate of decrease was roughly one db per statute
mile. This was in the 160 MHz range.
The mobile is so far away from the base that the received signal is
"noisy." I am considering rural locations and a terrain without significant
hills.

On the average, +3db of power at the base provided another 3 miles of
(poor quality) coverage. More often than not, coverage was limited by the
transmitter power of the mobile and the noise level at the base!

The question asked can start to be answered when one knows the value
placed on increased coverage.

73 Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:

I have a couple of GP-9s and can tell you the gain figures are a bit
inflated and not referenced to anything. A dipole array with optimum
spacing between dipoles is about the most gain for size that I have
encountered in VHF/UHF antennas. For VHF, a four bay dipole array at
20ft in length has 6dBD gain omni and the GP-9 claims 8.5dB(?) from
three 5/8 elements. On UHF, a 16 element dipole array has about 9.8dBD
gain and the GP-9 claims 11.9dB(?) for eight 5/8 elements. Something
looks fishy to me.
Mike


Ken Bessler wrote:
OK, after the thread on PL-259 losses, I figured
my system (ant gain - connector losses - coax loss)

150 mhz total net gain 1.006 DBi
450 mhz total net gain 2.797 DBi
Antenna tip is 32'6" above ground

My proposed system would replace the RG 58 coax pieces
with a single section of Flexi 4XL and the antenna would
be a Comet GP-9. The new figures a

150 mhz total net gain 7.919 DBi
450 mhz total net gain 10.553 DBi
Antenna tip is 47'6" above ground

150 mhz = 6.913 db improvement
450 mhz = 7.756 db improvement
Antenna tip 15 feet higher

Cost - about $250 for the improvement.

Now here's my question - will I notice the improvement
enough? I've had several OM's tell me that on SSB, CW
or HF I would but not on 2m/440 simplex and repeaters.


Ken KG0WX

"Mike" wrote in message
m...
I have a couple of GP-9s and can tell you the gain figures are a bit
inflated and not referenced to anything. A dipole array with optimum
spacing between dipoles is about the most gain for size that I have
encountered in VHF/UHF antennas. For VHF, a four bay dipole array at 20ft
in length has 6dBD gain omni and the GP-9 claims 8.5dB(?) from three 5/8
elements. On UHF, a 16 element dipole array has about 9.8dBD gain and the
GP-9 claims 11.9dB(?) for eight 5/8 elements. Something looks fishy to me.
Mike


Nothing can distpute your math - something's up.

I've changed plans a bit, though - the Boeing ARC 2 meter
repeater is only 4,000 feet away and I'm worried about
intermod. So, instead of a high gain antenna at 20', I'm going
to go with a moderate gain antenna 10' higher. The idea is
to get good gain with a farther horizon rather than high gain
with a closer horizon.

Plus, it's cheaper, too!

Instead of the GP-9 @ 20', I'm going to add a 10' mast
and go with a GP-3. Installation sould be a lot easier, too.
Now, though, my gain figures are 2.913 db improvement
on VHF and 3.056 db improvement on UHF.

I'm seriously starting to wonder if I should just leave well
enough alone - the MFJ-1729 is performing well. I was
talking to N0IDW on the 145.19 Winfield, KS machine
(a distance of 32 miles) and I could hit the reverse button
and hear him on the input. He, however, could not hear me
on the input.


Ken KG0WX

I've changed plans a bit, though - the Boeing ARC 2 meter
repeater is only 4,000 feet away and I'm worried about
intermod. So, instead of a high gain antenna at 20', I'm going
to go with a moderate gain antenna 10' higher. The idea is
to get good gain with a farther horizon rather than high gain
with a closer horizon.

Plus, it's cheaper, too!

Instead of the GP-9 @ 20', I'm going to add a 10' mast
and go with a GP-3. Installation sould be a lot easier, too.
Now, though, my gain figures are 2.913 db improvement
on VHF and 3.056 db improvement on UHF.

I'm seriously starting to wonder if I should just leave well
enough alone - the MFJ-1729 is performing well. I was
talking to N0IDW on the 145.19 Winfield, KS machine
(a distance of 32 miles) and I could hit the reverse button
and hear him on the input. He, however, could not hear me
on the input.


Ken KG0WX


Don't change the antenna but go for height and a good grade of coax. It
won't show up for about 50 feet or so of coax on 2 meters but if going to
100 feet of coax it will on 440.
If your setup is doing what you want it to put the money to something else.
I don't do too much with the repeaters and FM so I was just using some rg-59
(75 ohm coax) to a home made dipole about 20 feet up the tower. It does
what I want it to on FM. Unless it was to add some tower I would not spend
$ 250 for an FM antenna system just to work repeaters.