anyone out there using a parabolic grid antenna?

following on from my previous post, I bought the wlan grid antenna. Dissappointed. I've
got it connected to my PCI wireless card and I can't pick up a damn thing with it. Even my
little plastic usb stick picks up a couple of AP's but the grid - nothing. I've tried
contacting the supplier but had no response yet. To those that may be using a grid antenna
there was just one question I'd like to ask: what it the resistance across the terminals
on your antenna cable? ie: if you connect an ohm meter to the cable pin and housing what
reisistance do you get? On mine I get a short circuit, no resistance at all and I don't
know whether this is correct or not. I may have a faulty antenna.
I've got several other dinky wlan antennas and I tested all of them and they are all the
exact opposite - maximum resistance, not the slightest hint of continuity. I need to work
out if this grid antenna is faulty or not. Thanks for any feedback.

On Mon, 9 Jun 2008 21:12:02 +0100, "tg" <(E-Mail Removed)>
wrote:

>following on from my previous post, I bought the wlan grid antenna. Dissappointed. I've
>got it connected to my PCI wireless card and I can't pick up a damn thing with it. Even my
>little plastic usb stick picks up a couple of AP's but the grid - nothing. I've tried
>contacting the supplier but had no response yet. To those that may be using a grid antenna
>there was just one question I'd like to ask: what it the resistance across the terminals
>on your antenna cable? ie: if you connect an ohm meter to the cable pin and housing what
>reisistance do you get? On mine I get a short circuit, no resistance at all and I don't
>know whether this is correct or not. I may have a faulty antenna.
>I've got several other dinky wlan antennas and I tested all of them and they are all the
>exact opposite - maximum resistance, not the slightest hint of continuity. I need to work
>out if this grid antenna is faulty or not. Thanks for any feedback.

Any particular reason why you didn't bother mentioning the manufactory
and model number?

The feeds to most dish antennas are usually folded dipoles, which are
a DC short across the connector. Just to be sure, I checked several
Pacific Wireless dish antennas that happen to be cluttering my
balcony. Dead short.

Coaxial and colinear antennas are just a monopole with phasing
sections. No DC connection between center conductor and shield.

Some outdoor antennas have a DC short (1/2 wave loop stub) across the
coax connector in order to give it a DC path to ground. The problem
is static electricity will build up on the fiberglass radome and
eventually fry the electronics in the radio when discharged. The DC
short bleeds off the static electricity.

I can't tell from here what manner of problem you're having. Take
some photographs and post them to a photo gallery site so I can see
what you're doing.

Also, have you tried the stock rubber ducky antenna on your
unspecified model PCI card? Does it hear anything? If not, you may
have a dead or sick PCI card or broken sniffer software.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 (E-Mail Removed)
# http://802.11junk.com (E-Mail Removed)
# http://www.LearnByDestroying.com AE6KS

tg wrote:
> following on from my previous post, I bought the wlan grid antenna. Dissappointed. I've
> got it connected to my PCI wireless card and I can't pick up a damn thing with it.

> I've got several other dinky wlan antennas and I tested all of them and they are all the
> exact opposite - maximum resistance, not the slightest hint of continuity. I need to work
> out if this grid antenna is faulty or not. Thanks for any feedback.

Dish and grid antennas usually use a folded dipole which is a DC short.
Yagi and LPDA will show an open.
An omni will show open.
Patch antennas usually show open, but may show a short depending on the
internal feed configuration.

Are you sure you're not mixing an SMA with a Reverse SMA? They will
screw together, but the pins won't touch.

"Jeff Liebermann" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Mon, 9 Jun 2008 21:12:02 +0100, "tg" <(E-Mail Removed)>
> wrote:
>
> Any particular reason why you didn't bother mentioning the manufactory
> and model number?

no reason, just forgot Jeff sorry
this is my antenna (hope the link works)
http://www.wifi-link.com/product.php...8&product_id=4
2.4GHz Square GRID Parabolic Antenna 24dBi

thanks for the info you gave, at least I know now that it's normal for grid antennas to
read as a short with a ohm meter.
and I also took your advice and tried a different wireless card - wow what a difference. I
fiddled with the antenna direction and those signal bars shot up, so either my previous
card was faulty or it's just a weak old thing.
Thanks for your help.

"DTC" <(E-Mail Removed)> wrote in message
news:bZh3k.7312$(E-Mail Removed)...
>
> Are you sure you're not mixing an SMA with a Reverse SMA? They will screw together, but
> the pins won't touch.
>
thanks for your response DTC. See my above post, it seems I was using a junk card. Changed
the card, loads of signal now.

On Mon, 9 Jun 2008 23:46:41 +0100, "tg" <(E-Mail Removed)>
wrote:

>
>"Jeff Liebermann" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed).. .
>> On Mon, 9 Jun 2008 21:12:02 +0100, "tg" <(E-Mail Removed)>
>> wrote:
>>
>> Any particular reason why you didn't bother mentioning the manufactory
>> and model number?

>no reason, just forgot Jeff sorry
>this is my antenna (hope the link works)
>http://www.wifi-link.com/product.php...8&product_id=4
>2.4GHz Square GRID Parabolic Antenna 24dBi

The link works. They have an odd idea of what constitutes "square".
Very interesting video on assembling the antenna. Note the
orientation of the feed relative to the reflector grid. It's possible
to assemble the antenna with the feed rotated 90 degrees. The antenna
will function, but not very well.

>thanks for the info you gave, at least I know now that it's normal for grid antennas to
>read as a short with a ohm meter.

I have a similar feed torn apart somewhere. However, I didn't have
time to look for it.

>and I also took your advice and tried a different wireless card - wow what a difference. I
>fiddled with the antenna direction and those signal bars shot up, so either my previous
>card was faulty or it's just a weak old thing.
>Thanks for your help.

Congrats. Repair by substitution is my favorite.

A problem I've seen with PCI wi-fi cards is the RP-SMA connector just
falls apart, usually from excessive pressure by an oversized antenna,
connector, or pigtail. Give it a careful inspection. It's fairly
easy to reassemble.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 (E-Mail Removed)
# http://802.11junk.com (E-Mail Removed)
# http://www.LearnByDestroying.com AE6KS

"Jeff Liebermann" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Mon, 9 Jun 2008 23:46:41 +0100, "tg" <(E-Mail Removed)>
> wrote:

<snip>

> It's possible
> to assemble the antenna with the feed rotated 90 degrees. The antenna
> will function, but not very well.

are you saying the antenna will not function well if the feed is aligned wrong, or do you
mean this antenna will not fucntion well period?

> A problem I've seen with PCI wi-fi cards is the RP-SMA connector just
> falls apart, usually from excessive pressure by an oversized antenna,
> connector, or pigtail. Give it a careful inspection. It's fairly
> easy to reassemble.

yes I'm currently using a long pigtail type thing made of TV coax as a temporary measure
while I get used to this antenna. I'm sure an LM400 cable with adaptor would just rip the
sma socket connection right off the card ha ha.

tg wrote:
> are you saying the antenna will not function well if the feed is aligned wrong, or do you
> mean this antenna will not fucntion well period?

That depends...

You really can't misalign the antenna feed element as the mounting plate
will only attach one way (usually).

You can really bend it during shipment, but that would be obvious.

You can incorrectly orientate the antenna to horizontal polarization
if your AP is vertical.

In all cases, it would still work up close and perhaps a little further.
But in your case if its not working at all, I's say a bad or incorrect
coax connector or damaged wireless card connector.

On Jun 10, 5:17 am, "tg" <t...@nospamevereverever.net> wrote:

>....tried a different wireless card - wow what a difference. I fiddled with the antenna direction and those signal bars shot >up.....

I wonder - was it the new card, or the antenna direction that fixed
it ? With an extremely narrow 8 deg beamwidth, you could easily miss
everything due to mispointing...

> yes I'm currently using a long pigtail type thing made of TV coax as a temporary measure
> while I get used to this antenna. I'm sure an LM400 cable with adaptor would just rip the
> sma socket connection right off the card ha ha.


Sounds like you understand what you are doing, but it's possible that
your first attempt was a combination of off-target pointing and cable
loss combined.

On Tue, 10 Jun 2008 11:17:43 +0100, "tg" <(E-Mail Removed)>
wrote:

>"Jeff Liebermann" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed).. .
>> On Mon, 9 Jun 2008 23:46:41 +0100, "tg" <(E-Mail Removed)>
>> wrote:
>
><snip>
>
>> It's possible
>> to assemble the antenna with the feed rotated 90 degrees. The antenna
>> will function, but not very well.
>
>are you saying the antenna will not function well if the feed is aligned wrong, or do you
>mean this antenna will not fucntion well period?

Instead of the datasheet 24dBi gain, you'll get about 18dBi of gain
with a few extra side lobes. That was a common topic of discussion
long ago in a mailing list. A few of us intentionally assembled it
wrong, just to see what would happen.

>yes I'm currently using a long pigtail type thing made of TV coax as a temporary measure
>while I get used to this antenna. I'm sure an LM400 cable with adaptor would just rip the
>sma socket connection right off the card ha ha.

I use RG-6/u for 2.4GHz all the time. The 50 ohm to 75 ohm mismatch
is good for perhaps 0.5dB of loss, which is not much.
<http://www.qsl.net/n9zia/wireless/75_ohm_hardline.html>
The problem is the connector transitions between Type F and RP-SMA.
I've used the solid center wire from the RG-6/u to simulate the center
pin on an ordinary SMA plug, but you need the reverse. That usually
means at least 2 adapters. With really good adapters (gold and
teflon), the adapter losses are minimal. However, that's almost
impossible to find in Type F. So, I made my own, which show almost no
loss or reflection on the bench. Also, HyperLink used to sell a tower
mounted amplifier that used cheap 75 ohm coax instead of expensive LMR
50 ohm coax.


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