15dbi Yagi

Need BB · 07-23-2002

I bought one of these and it is far more directional than my coffe can antenna. Does this sound correct?

rogerRabbit · 07-23-2002

Yes.

(If nothing else: the higher the gain the narrower the pattern.)

(And if you're getting anywhere near 15dBi from a cantenna then I want to see it!)

Novilio · 07-23-2002

This might not be a bad place to ask, What do you guys do to measure the gain of a homebrew antenna? I've walked around antennas with a field strength meter (albeit at WAY lower frequencies) to sketch out a radiation pattern, but I've never attempted to get a db gain figure out of one. The ARRL Antenna Book describes the use of a calibrated standard gain antenna, but them creatures is rare in these parts.

On the other hand, building such an antenna for 2.4 Ghz couldn't be too hard. Some bent brazing rod on a 5" metal square should work. Has anybody done it?

Or are there simpler tricks I just haven't heard of?

--73--

--Novilio

lincomatic · 07-23-2002

lacking the proper equipment to do proper testing, most people just use the signal strength meters of their software against some standard antenna such as whatever built-in antenna is on their card. i usually use either ministumbler or the ORiNOCO client manager. that's why I never publish gain in dBi - just comparisons of performance.

can you describe in more detail your idea for a 15dBi yagi?

Novilio · 07-23-2002

Whoops, shoulda been more clear. The standard antenna I'm referring to is shown in a photo on page 27-35 of the ARRL Antenna Book, 15th Edition (1988.) It's not a Yagi at all; I'm not sure how it's characterized but it looks a little like a folded dipole.

I'm actually tinkering with waveguide antennas using 4" copper pipe and 4" galvanized stove ducting. Been a ham for 31 years but never played with microwaves until now. The simplicity of the waveguide design for microwave gain antennas is seductive compared to stringing fender washers on a threaded rod.

It would be nice to test directly in dB gain, but I've done all my testing so far just as you've described, using my laptop and NS. My FSM doesn't even twitch at 2.4 Ghz, even when I train the FAB parabolic on it.

There's something called The Zapchecker that they advertise in QST for $89 that's good to 4.5 GHz, and I'm tempted to get that. Not sure yet.

--73--

--Novilio

sparafina · 07-23-2002

Quote:

Originally posted by lincomatic
lacking the proper equipment to do proper testing, most people just use the signal strength meters of their software against some standard antenna such as whatever built-in antenna is on their card.

Have either one of you seen this link for a 2.4 ghz field strength meter?

http://www.mrx.com.au/wireless/TestGear2_4ghz.htm

Novilio · 07-23-2002

Quote:

Originally posted by sparafina
Have either one of you seen this link for a 2.4 ghz field strength meter?

Not until now...but I've got it bookmarked. I kind of wish he would have given the callout for that microwave diode. I have a couple of units in the junk trove that look EXACTLY like that, no idea where they came from; that stuff's been accumulating since 1963. Assuming my diodes are the Right Stuff, I have everything it would take to carve out one of those items in as few hours.

Thanks for the link. If I build one I'll post a report, with pictures.

--73--

--Novilio

lincomatic · 07-23-2002

Quote:

Originally posted by sparafina

Have either one of you seen this link for a 2.4 ghz field strength meter?

http://www.mrx.com.au/wireless/TestGear2_4ghz.htm

cool link. thanks. looks easy to build but i wonder how to calibrate it.

just went to www.zapchecker.com and strangely they don't even tell you how to buy it.

actually i am more interested in a vswr meter for tuning the antennae, but i'm not sure how the heck you use this frars contraption:

http://www.frars.org.uk/cgi-bin/render.pl?pageid=1085

do you just hook it to a DMM also?

anyone have any other links to a 2.4GHz SWR meter that's affordable?

lincomatic · 07-24-2002

here is an index of tons of homebrew test equipment, etc.

http://www.qsl.net/n9zia/wireless/appendixF.html#10

mr_wlan · 07-24-2002

http://www.frars.org.uk/cgi-bin/render.pl?pageid=1085 is the contraption being referred to.

Basically, the coupled line carries a small sample of the RF that's passing through the main line. Either end of the coupled line is a 50 ohm load and a detector diode - both diodes are the same type. To measure the forward and reflected power is a simple case of measuring the voltages across the diodes. From this you can use the simple vswr calculation to determine SWR.

I'll knock up a simple meter circuit and put on the page if that will help?

Ah yes also have a look at the wireless lan antenna testing day pictures - this will give u some idea of what u need to measure gain and polar pattern.

regards,

mr_wlan

lincomatic · 07-24-2002

Quote:

Originally posted by mr_wlan
[BBasically, the coupled line carries a small sample of the RF that's passing through the main line. Either end of the coupled line is a 50 ohm load and a detector diode - both diodes are the same type. To measure the forward and reflected power is a simple case of measuring the voltages across the diodes. From this you can use the simple vswr calculation to determine SWR.

I'll knock up a simple meter circuit and put on the page if that will help?
[/b]

mr_wlan,
can i just hook up a DVM across the diodes?
what are the relevant formulae?
TIA,

Novilio · 07-24-2002

Quote:

Originally posted by lincomatic
just went to www.zapchecker.com and strangely they don't even tell you how to buy it.

The Zapchecker guys run a regular ad in QST. I'm looking at the August issue, page 129. Here are the particulars:

Zapchecker, $89, including shipping & handling. CA residents add 8% sales tax.

Alan Broadband Company
93 Arch Street
Redwood City CA 94062
(888) 369-9627 Orders
(650) 369-9627 FAX/Phone
www.zapchecker.com

Looks good, but I think I'll try building that Australian lashup first and see how it works before I lay out $89 for something that I can duplicate in an evening by picking up some junk laying on the garage floor...

--73--

--Novilio

07-23-2002	#1 (permalink)
Need BB Registered Member Join Date: Jun 2002 Posts: 11	15dbi Yagi I bought one of these and it is far more directional than my coffe can antenna. Does this sound correct? __________________ I NEED SOME BB

07-23-2002	#2 (permalink)
rogerRabbit Peripatetic Stumbler Join Date: Jun 2002 Location: Motueka Posts: 219	Yes. (If nothing else: the higher the gain the narrower the pattern.) (And if you're getting anywhere near 15dBi from a cantenna then I want to see it!) Last edited by rogerRabbit : 07-23-2002 at 07:58 AM.

07-23-2002	#4 (permalink)
lincomatic Squaaawk! WiFi! WiFi! Join Date: Apr 2002 Location: Tinsel Town Posts: 1,682	lacking the proper equipment to do proper testing, most people just use the signal strength meters of their software against some standard antenna such as whatever built-in antenna is on their card. i usually use either ministumbler or the ORiNOCO client manager. that's why I never publish gain in dBi - just comparisons of performance. can you describe in more detail your idea for a 15dBi yagi? __________________ ~lincomatic

07-24-2002	#9 (permalink)
lincomatic Squaaawk! WiFi! WiFi! Join Date: Apr 2002 Location: Tinsel Town Posts: 1,682	here is an index of tons of homebrew test equipment, etc. http://www.qsl.net/n9zia/wireless/appendixF.html#10 __________________ ~lincomatic

07-24-2002	#10 (permalink)
mr_wlan Registered Member Join Date: Apr 2002 Posts: 40	i'm not sure how the heck you use this frars contraption: http://www.frars.org.uk/cgi-bin/render.pl?pageid=1085 is the contraption being referred to. Basically, the coupled line carries a small sample of the RF that's passing through the main line. Either end of the coupled line is a 50 ohm load and a detector diode - both diodes are the same type. To measure the forward and reflected power is a simple case of measuring the voltages across the diodes. From this you can use the simple vswr calculation to determine SWR. I'll knock up a simple meter circuit and put on the page if that will help? Ah yes also have a look at the wireless lan antenna testing day pictures - this will give u some idea of what u need to measure gain and polar pattern. regards, mr_wlan

07-23-2002	#3 (permalink)
Novilio ScrivenStumbler Join Date: Jul 2002 Location: Colorado Springs, CO Posts: 254	This might not be a bad place to ask, What do you guys do to measure the gain of a homebrew antenna? I've walked around antennas with a field strength meter (albeit at WAY lower frequencies) to sketch out a radiation pattern, but I've never attempted to get a db gain figure out of one. The ARRL Antenna Book describes the use of a calibrated standard gain antenna, but them creatures is rare in these parts. On the other hand, building such an antenna for 2.4 Ghz couldn't be too hard. Some bent brazing rod on a 5" metal square should work. Has anybody done it? Or are there simpler tricks I just haven't heard of? --73-- --Novilio

07-23-2002	#5 (permalink)
Novilio ScrivenStumbler Join Date: Jul 2002 Location: Colorado Springs, CO Posts: 254	Whoops, shoulda been more clear. The standard antenna I'm referring to is shown in a photo on page 27-35 of the ARRL Antenna Book, 15th Edition (1988.) It's not a Yagi at all; I'm not sure how it's characterized but it looks a little like a folded dipole. I'm actually tinkering with waveguide antennas using 4" copper pipe and 4" galvanized stove ducting. Been a ham for 31 years but never played with microwaves until now. The simplicity of the waveguide design for microwave gain antennas is seductive compared to stringing fender washers on a threaded rod. It would be nice to test directly in dB gain, but I've done all my testing so far just as you've described, using my laptop and NS. My FSM doesn't even twitch at 2.4 Ghz, even when I train the FAB parabolic on it. There's something called The Zapchecker that they advertise in QST for $89 that's good to 4.5 GHz, and I'm tempted to get that. Not sure yet. --73-- --Novilio

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