RadioBanter - Matching on the MFJ-1800

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Matching on the MFJ-1800

"Richard Clark" wrote in message
...
On Fri, 20 Nov 2009 18:26:17 -0600, "amdx" wrote:

Hi Richard,
What do you mean by "lack of driven element symmetry" ?
Mike
Hi Mike,

The driven loop is not symettrical to the plane of the directors and
reflector, thus it peers down (or up, or to the side - depending on
deployment).
Look boresight down the boom. The loop is off-center.

73's
Richard Clark, KB7QHC

Good, I thought that might be the answer but wanted to check.
Glad I added that detail to the drawing, do you think that is
engineered to control output impedance?
What happens to the impedance if you center it?

Could you post your model or send it to me, I have a fellow
ham that tried to model the FD and could not get it to work.
He would like to see one that does work and find out what he did wrong.
Eznec if you have it.
Thanks, Mike

Matching on the MFJ-1800

On Sat, 21 Nov 2009 06:24:49 -0600, "amdx" wrote:

Could you post your model or send it to me, I have a fellow
ham that tried to model the FD and could not get it to work.
He would like to see one that does work and find out what he did wrong.
Eznec if you have it.
Thanks, Mike

Hi Mike,

It has been posted to you as you asked. Jeff also has a copy.

Can you tell us what you mean about your buddy's model and how he
"could not get it to work?" Did he follow your dimensions?

73's
Richard Clark, KB7QHC

Matching on the MFJ-1800

"Richard Clark" wrote in message
...
On Sat, 21 Nov 2009 06:24:49 -0600, "amdx" wrote:

Could you post your model or send it to me, I have a fellow
ham that tried to model the FD and could not get it to work.
He would like to see one that does work and find out what he did wrong.
Eznec if you have it.
Thanks, Mike

Hi Mike,

It has been posted to you as you asked. Jeff also has a copy.

Can you tell us what you mean about your buddy's model and how he
"could not get it to work?" Did he follow your dimensions?

73's
Richard Clark, KB7QHC

He's out of town for a couple of days, when he returns I'll quiz him.
Mike

Matching on the MFJ-1800

Comparision NO Feedback??

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. :-)

Matching on the MFJ-1800

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

Matching on the MFJ-1800

"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.

Matching on the MFJ-1800

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