"Jeff Liebermann" wrote in message
...
On Thu, 19 Nov 2009 06:05:20 -0600, "amdx" wrote:

I have found the need to work for a living, gets in the way of a lot of
fun!

5 hours on the phone on a slow motion conference call this morning.
Absolutely nothing useful accomplished. Such online meetings should
be banned, taxed, or both as a threat to national productivity.

I took the coax loose on the MFJ-1800 and and removed the toroids, I found
the letters found M1Z/111-RG and then the insulation ended. Argh!
Oh, I have a second antenna, so I took that one apart, Eureka! RGS-303
http://wireandcable.thermaxcdt.com/i...d-70-?&seo=110
50 ohm coax. PTFE center insulator, FEP jacket.
Mike

Thanks. 50 ohm coax does not make it a matching section to a 200 ohm
folded dipole. However, the ferrite beads are a good way to simply
block the reflected power from the folded dipole so that it looks like
it's matched. In any case, that reflected power is lost (converted to
heat) in the ferrite beads. So much for efficiency. When I change
the characteristic impedance of the model from 200 ohms to 50 ohms,
the VSWR climbs to 5.5:1. Yech. (Note that the radiation efficiency
is 75% with or without the mismatch).

I suppose the antenna could be made to function by replacing the coax
section with a real 1/4 wave 4:1 balun, but I'll leave that to MFJ to
figure out.

If you need some more entertainment value, it would be interesting to
actually measure the gain of the antenna. Find a known good reputable
antenna with similar gain. A panel or patch will work. Find a signal
source that isn't infested with reflections (including ground
reflections), Fresnel Zone issues, and is fairly stable (i.e. doesn't
physically move). Use Netstumbler, WirelessMon, or Kismet to compare
the signal strengths. For additional accuracy, use a step attenuator
to adjust the signal levels to a common reference level. Better yet,
use a spectrum analyzer.
Jeff Liebermann

Sure, as soon as I try to make you King you find work for me :-)

Ya, I have quad panel on the boat, when I get some time I'll try the
comparision.
BTW, I had a friend purchase an Alfa-Awus-036 Wifi Adapter.
He said it worked very well! So I ordered one, I replaced a TP-Link
TL-WN321G
with the Alfa-Awus-036. I had 23 signals received with only about 4 usable
signals on the
TL-WN321G. After I installed the Alfa I received 36 signals and all of them
have a signal
strength that would make them usable. (Of course some are encrypted)
This thing screams! I had used the TL-WN321G for several years and thought
it was good
until I tried the Alfa.
http://www.amazon.com/Adapter-Wardri...7004388&sr=8-4
I'm using it with a 19dbi* panel antenna aimed a a 7 story condo.
http://www.fab-corp.com/product.php?...cat=255&page=1
Thanks, for all the input guys.
* advertised

On Thu, 19 Nov 2009 18:46:59 -0600, "amdx" wrote:

Sure, as soon as I try to make you King you find work for me :-)

I hate to tell you this, but that's what kings are paid to do. They
give orders. Do you require a public proclamation, executive order,
or pontifical bull (in Latin), in order to be properly inspired? Now,
pleae do some testing. After all this is your antenna, your question
and your problem.

Ya, I have quad panel on the boat, when I get some time I'll try the
comparision.

Doing it on a boat might be a problem. You're too close to the water
which will probably be inside the Fresnel Zone. The water also acts
as a great reflector. Thinks also move on a vessel, making stable
readings difficult. I do my testing across a valley, where there's
little chance of ground reflections (and there's a convenient 2.4GHz
RF source from the local mountain top WISP). The path also has a wall
of 40 meter high trees on both side to attenuate any interference.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
On Thu, 19 Nov 2009 18:46:59 -0600, "amdx" wrote:

Sure, as soon as I try to make you King you find work for me :-)

I hate to tell you this, but that's what kings are paid to do. They
give orders. Do you require a public proclamation, executive order,
or pontifical bull (in Latin), in order to be properly inspired? Now,
pleae do some testing. After all this is your antenna, your question
and your problem.

Ya, I have quad panel on the boat, when I get some time I'll try the
comparision.

Doing it on a boat might be a problem. You're too close to the water
which will probably be inside the Fresnel Zone. The water also acts
as a great reflector. Thinks also move on a vessel, making stable
readings difficult. I do my testing across a valley, where there's
little chance of ground reflections (and there's a convenient 2.4GHz
RF source from the local mountain top WISP). The path also has a wall
of 40 meter high trees on both side to attenuate any interference.

Jeff Liebermann

All that may be true, sorry King, is true.
My antennas are 14ft above the water and the signal only goes over water for
about 30ft
before a concrete parking lot fills the rest of the distance to my targets.
Total target distance
is about 600ft. The antennas are tipped upward about 10 degrees.
Here's the test I performed, I aligned the panel and the yagi on a pole
with about the 2ft between the yagi and the center of the panel. I aimed at
the target as
accurately a I could see. (Center of condo building) During testing I did
not terminate the unused
antenna.
I used net stumbler for signal strength numbers, I received 42 signals with
the Panel,
and 44 signals with the yagi.
The one signal I usually use went from -48db (panel) to -50db (yagi),
That's +2db for the Panel.
Then I did a Netstumbler screen print of the first 35 signals using the yagi
and then the panel.
I added all 35 signal strengths and divided by the 35, to get an average
signal.
(35 is all that fit the screen without scrolling)
The Panel AVE = -58.11db, the Yagi AVE = 59.9db that is + 1.79db for the
Panel.
So if you have any faith in my method, it looks like the yagi is down about
2db from the Panel.
I'm impressed, the MFJ-1800 yagi is advertised as a 15dbi antenna, the
panel
as 19dbi antenna.
Here's the Panel seller for the 19dbi panel antenna.
http://www.fab-corp.com/product.php?...cat=255&page=1
At one time I found antenna plots for it, but can't locate them now.
Here's the yagi seller.
http://www.mfjenterprises.com/Produc...uctid=MFJ-1800
Thanks, Mike
PS.
Previously a saw 33 signals, I had never tried to optimize by adjusting the
antenna, 33 was
good enough. While mounting the yagi I moved the position of the panel,
looks like
I found a better position. :-)

I'll try the
comparision.

Doing it on a boat might be a problem. You're too close to the water
which will probably be inside the Fresnel Zone. The water also acts
as a great reflector. Thinks also move on a vessel, making stable
readings difficult. I do my testing across a valley, where there's
little chance of ground reflections (and there's a convenient 2.4GHz
RF source from the local mountain top WISP). The path also has a wall
of 40 meter high trees on both side to attenuate any interference.

Jeff Liebermann

All that may be true, sorry King, is true.
My antennas are 14ft above the water and the signal only goes over water
for about 30ft
before a concrete parking lot fills the rest of the distance to my
targets. Total target distance
is about 600ft. The antennas are tipped upward about 10 degrees.
Here's the test I performed, I aligned the panel and the yagi on a pole
with about the 2ft between the yagi and the center of the panel. I aimed
at the target as
accurately a I could see. (Center of condo building) During testing I did
not terminate the unused
antenna.
I used net stumbler for signal strength numbers, I received 42 signals
with the Panel,
and 44 signals with the yagi.
The one signal I usually use went from -48db (panel) to -50db (yagi),
That's +2db for the Panel.
Then I did a Netstumbler screen print of the first 35 signals using the
yagi and then the panel.
I added all 35 signal strengths and divided by the 35, to get an average
signal.
(35 is all that fit the screen without scrolling)
The Panel AVE = -58.11db, the Yagi AVE = 59.9db that is + 1.79db for the
Panel.
So if you have any faith in my method, it looks like the yagi is down
about 2db from the Panel.
I'm impressed, the MFJ-1800 yagi is advertised as a 15dbi antenna, the
panel
as 19dbi antenna.
Here's the Panel seller for the 19dbi panel antenna.
http://www.fab-corp.com/product.php?...cat=255&page=1
At one time I found antenna plots for it, but can't locate them now.
Here's the yagi seller.
http://www.mfjenterprises.com/Produc...uctid=MFJ-1800
Thanks, Mike
PS.
Previously a saw 33 signals, I had never tried to optimize by adjusting
the antenna, 33 was
good enough. While mounting the yagi I moved the position of the panel,
looks like
I found a better position. :-)

On Fri, 20 Nov 2009 13:18:15 -0600, "amdx" wrote:


"Jeff Liebermann" wrote in message
.. .
On Thu, 19 Nov 2009 18:46:59 -0600, "amdx" wrote:

Sure, as soon as I try to make you King you find work for me :-)

I hate to tell you this, but that's what kings are paid to do. They
give orders. Do you require a public proclamation, executive order,
or pontifical bull (in Latin), in order to be properly inspired? Now,
pleae do some testing. After all this is your antenna, your question
and your problem.

Ya, I have quad panel on the boat, when I get some time I'll try the
comparision.

Doing it on a boat might be a problem. You're too close to the water
which will probably be inside the Fresnel Zone. The water also acts
as a great reflector. Thinks also move on a vessel, making stable
readings difficult. I do my testing across a valley, where there's
little chance of ground reflections (and there's a convenient 2.4GHz
RF source from the local mountain top WISP). The path also has a wall
of 40 meter high trees on both side to attenuate any interference.

Jeff Liebermann

All that may be true, sorry King, is true.

What a king says is by definition true, even if it's wrong.

My antennas are 14ft above the water and the signal only goes over water for
about 30ft
before a concrete parking lot fills the rest of the distance to my targets.
Total target distance
is about 600ft. The antennas are tipped upward about 10 degrees.

Sounds good. You're out of the Fresnel Zone and the parking lot isn't
going to contribute any reflections.

Here's the test I performed, I aligned the panel and the yagi on a pole
with about the 2ft between the yagi and the center of the panel.

Not so good. You can't leave a bunch of potentially resonant metal
hanging around that close to the antenna. The unsused antenna could
easily be re-radiating anything it pickups up from the other antenna.
One antenna at a time please.

I aimed at
the target as
accurately a I could see. (Center of condo building) During testing I did
not terminate the unused
antenna.

Ugh. If you're shooting into what's essentially and indoor wireless
router, you're going to get reflections from the building and in
particular, from the room where the AP is located. Also, not so good.

I used net stumbler for signal strength numbers, I received 42 signals with
the Panel,
and 44 signals with the yagi.

How steady were the readings? With my experience with Netstumbler, if
I wait a few minutes, the readings will move around perhaps 2-5dB. Are
you doing this on Channel 6 (middle of the band) or near the band
edges?

The one signal I usually use went from -48db (panel) to -50db (yagi),
That's +2db for the Panel.
Then I did a Netstumbler screen print of the first 35 signals using the yagi
and then the panel.
I added all 35 signal strengths and divided by the 35, to get an average
signal.
(35 is all that fit the screen without scrolling)
The Panel AVE = -58.11db, the Yagi AVE = 59.9db that is + 1.79db for the
Panel.

Good idea but not really valid as you're probably measauring the side
lobes of the antennas. An antenna with many side lobes is going to
hear more stations than one with just a single major lobe.

So if you have any faith in my method, it looks like the yagi is down about
2db from the Panel.
I'm impressed, the MFJ-1800 yagi is advertised as a 15dbi antenna, the
panel
as 19dbi antenna.

I have less faith in the RSSI linearity of thatever you're using for a
wireless device. -50dBm isn't particularly saturated, so presumably,
the comparison is valid. There might be some gain compression at high
signal levels, which explains why you're seeing 2dB difference instead
of 4dB. I would have predicted a larger difference as my NEC model of
the MFJ-1800 predicts a gain of about 13dBi. I would have expected an
even larger difference.

Here's the Panel seller for the 19dbi panel antenna.
http://www.fab-corp.com/product.php?...cat=255&page=1
At one time I found antenna plots for it, but can't locate them now.
Here's the yagi seller.
http://www.mfjenterprises.com/Produc...uctid=MFJ-1800

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
On Fri, 20 Nov 2009 13:18:15 -0600, "amdx" wrote:


"Jeff Liebermann" wrote in message
. ..
On Thu, 19 Nov 2009 18:46:59 -0600, "amdx" wrote:

Sure, as soon as I try to make you King you find work for me :-)

I hate to tell you this, but that's what kings are paid to do. They
give orders. Do you require a public proclamation, executive order,
or pontifical bull (in Latin), in order to be properly inspired? Now,
pleae do some testing. After all this is your antenna, your question
and your problem.

Ya, I have quad panel on the boat, when I get some time I'll try the
comparision.

Doing it on a boat might be a problem. You're too close to the water
which will probably be inside the Fresnel Zone. The water also acts
as a great reflector. Thinks also move on a vessel, making stable
readings difficult. I do my testing across a valley, where there's
little chance of ground reflections (and there's a convenient 2.4GHz
RF source from the local mountain top WISP). The path also has a wall
of 40 meter high trees on both side to attenuate any interference.

Jeff Liebermann

All that may be true, sorry King, is true.

What a king says is by definition true, even if it's wrong.

My antennas are 14ft above the water and the signal only goes over water
for
about 30ft
before a concrete parking lot fills the rest of the distance to my
targets.
Total target distance
is about 600ft. The antennas are tipped upward about 10 degrees.

Sounds good. You're out of the Fresnel Zone and the parking lot isn't
going to contribute any reflections.

Here's the test I performed, I aligned the panel and the yagi on a pole
with about the 2ft between the yagi and the center of the panel.

Not so good. You can't leave a bunch of potentially resonant metal
hanging around that close to the antenna. The unsused antenna could
easily be re-radiating anything it pickups up from the other antenna.
One antenna at a time please.

Ok, measuring antennas is never easy, I'll hopefully get some time next
week.
I won't bore you with the details, but the campaign I'm running is
eventually going to have the party overthrow a king. :-)
I'll install one antenna at a time.

I aimed at
the target as
accurately a I could see. (Center of condo building) During testing I did
not terminate the unused
antenna.

Ugh. If you're shooting into what's essentially and indoor wireless
router, you're going to get reflections from the building and in
particular, from the room where the AP is located. Also, not so good.


Well, I guess I'm $#%^ed.

Measuring antennas is never easy.


I used net stumbler for signal strength numbers, I received 42 signals
with
the Panel,
and 44 signals with the yagi.

How steady were the readings? With my experience with Netstumbler, if
I wait a few minutes, the readings will move around perhaps 2-5dB. Are
you doing this on Channel 6 (middle of the band) or near the band
edges?


I didn't see any changes but I only paid attention to the one signal I
normally use.

I received on the channel the source transmited on.

Here's a file of the two screenprints with channel and signal strength.

http://i395.photobucket.com/albums/p...fiantennas.jpg

For what its worth.


The one signal I usually use went from -48db (panel) to -50db (yagi),
That's +2db for the Panel.
Then I did a Netstumbler screen print of the first 35 signals using the
yagi
and then the panel.
I added all 35 signal strengths and divided by the 35, to get an average
signal.
(35 is all that fit the screen without scrolling)
The Panel AVE = -58.11db, the Yagi AVE = 59.9db that is + 1.79db for the
Panel.

Good idea but not really valid as you're probably measauring the side
lobes of the antennas. An antenna with many side lobes is going to
hear more stations than one with just a single major lobe.


Who knows, I think the whole condo is in the major lobe and nothing but
water

on one side and on the other side I doubt there are any signals. I do recall
one -80 db

signal so maybe something in the side lobe.


So if you have any faith in my method, it looks like the yagi is down
about
2db from the Panel.
I'm impressed, the MFJ-1800 yagi is advertised as a 15dbi antenna, the
panel
as 19dbi antenna.

I have less faith in the RSSI linearity of thatever you're using for a
wireless device. -50dBm isn't particularly saturated, so presumably,
the comparison is valid. There might be some gain compression at high
signal levels, which explains why you're seeing 2dB difference instead
of 4dB. I would have predicted a larger difference as my NEC model of
the MFJ-1800 predicts a gain of about 13dBi. I would have expected an
even larger difference.



Measuring antennas is never easy.

I note my laptop within 20ft of the router has a -36db signal using
netstumbler.

Thanks for your help Jeff,

Mike

Thanks to Richard too.

On Sat, 21 Nov 2009 18:14:42 -0600, "amdx" wrote:

Here's a file of the two screenprints with channel and signal strength.

http://i395.photobucket.com/albums/p...fiantennas.jpg

For what its worth.

Hi Mike,

Seems like hardly a difference (within half a dB) of each other.

73's
Richard Clark, KB7QHC