impedance tuned antenna

Impedance mismatch causes loss of energy transfer between the two sides, send and receive. The greater the mismatch the greater the loss.

My wireless card (rather old PCMCIA card) has a built-in antenna, which is sensitive enough for use inside my home, I don't use an additional antenna.

-- Julio

"Spacey Spade" hath wroth:

That's like asking how important is having the tires on an automobile properly balanced. At slow speeds, it doesn't matter much. At high speeds, you can lose control.

The same thing applies to mismatching antennas. The problem is that the effect is often not noticeable with common wireless devices. For example, this contrivance is a badly constructed Biquad 2.4GHz antenna.

are a bunch of web pages that built it wrong, yet still had good results and gain improvments. The minimum VSWR is 6:1 which is horrible for any antenna. Yet, it sorta works.

The same thing applies to many of the home made coffee can, franklin, biquad, colinear, etc. The builder doesn't really know what the VSWR of his antenna is without proper test equipment. I recently aquired some test equipment. The first thing I did was test my various home made antennas. The results were both disappointing and dismal. In almost all cases, my attempts to tune the antenna by maximum gain, resulted in the minimum VSWR point being way off frequency. Yet, the antennas work well enough.

So, what's happening? The way it works is that almost *ANY* antenna, no matter how badly built, is an improvment over the stock 2dBi vertical coaxial antenna. Even badly built, it will provide an improvment in gain. The VSWR can be truely horrible, and the antenna will still function.

I have no idea how much trouble you will have because I have no clue as to how much experience, expertise, and equipment you have to work with. My guess(tm) is that if you have to ask such a question, you're starting from scratch. If you don't mind destroying a few devices, it's possible to attach an external antenna, coax cable pigtail, or coax connector to almost anything. For example:

a pigtail on a Dlink DWL-650. What's important is that the exposed center conductor to board connection must be kept VERY short. You'll need a very small soldering iron tip, good eyesight, a steady hand, and a good selection of profanity, to do this properly. Of course knowing exactly where to attach the antenna can be a problem.

Good luck and welcome to Learn By Destroying(tm).

Thanks Jeff, your info is priceless

I just came accross the following wiki, which has nothing to do with this topic, but what a wealth of specifications for cards it is!!!

I'm quoting a bit of it just in case it goes 404... [quote] Receive Sensitivity is how much signal a card needs to receive in order to work at that speed level. A 3 dB difference is double the power. You can now see some cards are getting much better distances. The difference between a Cisco 350 and a Addtron at 1 Mbps is 32x times the sensitivity. This means that the Cisco needs 1/32 as much signal strength as the Addtron does to work at the same rate. Also, a lower receive sensitivity number is better (IE: -95 is better than -80). Receive sensitivity is measured in dBm @BER 10E-5 or (or 8% FER).

Note: IEEE 802.11 15.4.8.1 says that "F" in 8% FER for DSSS devices stands for an MPDU having 1024 octets. 8/100 (errors/frames) / (1024 (octets) * 8 (bits) = approx. 1/100,000 errors/bits = 10-5 BER. i.e. 8% FER should be comparable to 10-5 BER.

Card 1 Mbps 2 Mbps 5.5 Mbps 11 Mbps Note Demarc(300mW, RP-MMCX connectors) -96 -95 -93 -91 With EMF Protection Demarc(200mW, RP-MMCX connectors) -96 -95 -93 -91 With EMF Protection Demarc(100mW, RP-MMCX connectors) -96 -95 -93 -91 With EMF Protection Senao NL/SL-2511CD PLUS (200mW, no EXT antenna) -95 -93 -91 -89 Unofficial Senao Support Webpage Senao NL/SL-2511CD PLUS EXT2 (200mW, 2 MMCX connectors) -95 -93 -91 -89 Unofficial Senao Support Webpage EnGenius NL/EL-2511CD PLUS (200mW, no EXT antenna) -95 -93 -91 -89 same as Senao NL-2511CD PLUS EnGenius NL/EL-2511CD PLUS EXT2 (200mW, 2 MMCX connectors) -95 -93 -91 -89 same as Senao NL-2511CD PLUS EXT2 SonicWALL Long Range Wireless Card (200mW, no EXT antenna) -95 -93 -91 -89 OEM Senao NL-2511CD PLUS; see this FAQ MacSense WPE-700 (200mW) -95 -93 -90 -87 OEM Senao NL-2511CD PLUS, MAC OS support! smartBridges airNIC (32mW, USB, SMA connector) -95 -90 -89 -84 Zcom/Zcomax XI-325HP (200mw, 2 RP-MMCX connectors) -94 -93 -91 -89

SMC SMC2532W-B (200mW, 2 RP-MMCX connectors) -94 -93 -91 -89 OEM Zcom XI-325HP Cisco 350 Series (100mW) -94 -91 -89 -85 Compaq MultiPort W200 (32mW, MC? connector) -94 -91 -87 -85 Lucent/Agere/Proxim Orinoco Gold/Silver Card (32mW) -94 -91 -87 -82

Enterasys Roamabout pcmcia -94 -91 -87 -82 Dell ?TrueMobile 1150 (32mW) -94 -91 -87 -82 OEM Orinoco Gold Compaq WL-110 (32mW) -94 -91 -87 -82 OEM Orinoco Gold Proxim USB 842x . -88 . -84 has u.FL connector inside case PCB smartBridges airBridge (100mW, RJ45, SMA connector) -94 -88 -87 -84

smartBridges airBridge Outdoor (100mW, RJ45, N Bulkhead) -94 -88 -87 -84 Nokia C110/C111(35mW) -94 . . -83 Senao SL-2011CD PLUS (100mW, no EXT antenna) -93 -91 -89 -87 Unofficial Senao Support Webpage Senao SL-2011CD PLUS EXT2 (100mW, 2 MMCX connectors) -93 -91 -89 -87 Unofficial Senao Support Webpage Senao SL-2511CD (50mW, no EXT antenna) -93 -91 -89 -87 Unofficial Senao Support Webpage Alvarion DS.11 bridge (250mW) -93 -90 -88 -85 smartBridges airCarte -93 -88 -87 -84 Aironet 4800A (100mW) -93 -90 -83 -80 PCMCIA card in proprietary PCMCIA carrier Siemens SpeedStream SS1021 (63mW, no EXT antenna) -92 -90 -87 -84 Zcom/Zcomax XI-325B (32mW, 2 RP-MMCX connectors) -92 -89 -88 -85 ZyXEL ZyAIR B-100 (80mW) -92 -89 -86 -85 ZyXEL ZyAIR B-101 (32mW) -92 -89 -88 -85 OEM Zcom XI-325B ZyXEL ZyAIR B-200 (63mW) -92 -89 -86 -85 Zcom/Zcomax XI-325H (100mw, RP-MMCX connectors) -92 . . -85 Netgear MA401 (PCMCIA) -92 -88 -87 -84 [/quote]

Don't worry. I'll send you my price list and rate card.

Grrrr... I posted some objections to that page a few years ago. Many of the numbers are lifted directly from the manufacturers specification sheets. In several cases, the numbers are from the chipset and not the actual radio and does not include losses incurred by the diversity switch, circuit board losses, internal pigtail, or external connector. There's no clue as to where the numbers came from, or how the tests were made (or even if there were any tests performed). It's fairly difficult to do a proper sensitivity test as it requires a BER (bit error rate) or PER (packet error rate) tester and possibly an RF screen room. (Note: PER is same as FER). In addition, the 8% PER changed to 10% FER for 802.11g oFDM speeds making the chart rather old. Lastly, there's no consideration for the typical performance spread, which can be substantial.

See: |

roughly how some vendors measure sensitivity.

Some clues as to what the numbers mean: |

It won't. It's been around a long time and is a very popular page.

I keep looking for an easy way out because I've got so much to do, and... OMG, let me quote one of my clients: Spacey, "you're really good and competent. Sorry, I'm just looking for an easy way to get somewhere."

She does photography and is venturing into digital photography. There is no way she can learn all I know, and there is no way I can learn all you know. And everyone thinks they should get information for free. Which would be fine if I didn't have to make a living. To a certain extent, I've stopped trying to figure all this stuff out, and be a little more practical, so that I can at least do the day to day stuff without going mad.

I was talking to a gorgeous student (ex-cheerleader at a college) who was going towards practicing law in the medical field. She said she wanted to make a difference. I was impressed (cause to me it sounds like trying to stop a stampede of elephants that are acting like lemmings). But you know, based on the group I was hanging with, I was not surprised that she had no interest in discussing the moral issues. Those kinds of questions impede financial gain, which is decorated as being for the glory of God.

Jeff, refresh my memory. Where are the plans for your "good" biquad.

I've got an HP8660C with the 2.6Ghz plug in. However, I don't have anything to measure VSWR at those frequencies.

snipped-for-privacy@sushi.com hath wroth:

(learn to edit the quoted part of a posting).

I don't think the HP 8660c has an RF detector or DC amplifier and may be difficult to use with a VSWR bridge. Also, does the sweep range on the HP 8660c do a 100MHz or more wide sweep at 2.4GHz? If not, it won't be useable. It's difficult to tweak antennas without a wide range sweep. Actually, it's difficult even with a wide range sweep as there are VSWR peaks and nulls in all manner of strange locations.

What I have are these: |

| | the Wiltron sweep generator on eBay above only goes to

110Mhz. I have both the 4GHz and 8GHz plugins. The scalar network analyzer isn't really necessary as I can do most of what I need with just a scope. Photos when I get done patching my leaky roof and redecoratig the workbench.

| Actually, the Wiltron sweep generator on eBay above only goes to

The only VSWR measurements I've done are with a Diamond meter. [BTW, I have the one that goes to 1.2G. I don't know if it will be good at

2.4G.

Regarding the Anritsu bridge, it's not very clear, but I assume one port is measuring the reflected energy. Can't I juse feed this to a RF power meter?

| Actually, the Wiltron sweep generator on eBay above only goes to

My Dutch is about as good as my Greek, however I think this design

scaling the loops to account for the velocity factor. That is, I believe the loops are 116mm in circumference, but 4*30.5=122mm. I wonder if getting a small piece of 1-1/2 inch pipe and cutting a sliver is better than bending copper wire. The pipe would be less likely to bend in the horizontal plane.

snipped-for-privacy@sushi.com hath wroth:

It won't work. If desperate, find a directional coupler and two diode detectors. Or just build a vswr bridge:

Worth going through the entire site:

Oops. Wrong data sheet. I have a Wiltron 59A50. This one is similar, but not identical:

are 4 ports. Device under test, reference termination, sweep generator in, and diode detector out. The diode detector goes to a DC coupled amplifier and then to the scope or display unit. Some sweepers have this amplifier built or you can use the amp in the scope. The detected voltages are in the millivolt range because the VSWR bridge is normally run at very low RF levels. It's not like your Diamond meter, which has watts to spare.

Really awful scan of the 59A50 manual: | http://p3.hostingprod.com/@rfbroadcast.com/ebay/PDF/wiltronautotester.pdf However, the above is a scalar (non-vector) network analyzer. You get the value of the VSWR, but not whether it's inductive or capacitive. For that, you need a vector network analyzer.

Got money? Buy me one of these: |

one of the other network analyzers.

Photos tomorrow. I'm dead tired.

snipped-for-privacy@sushi.com hath wroth:

(edit, edit, edit, edit...)

Nope. The cazapitance to the ground plane tends to shorten the loop slightly. There's also end dispersion effects. The relatively large diameter to wavelength ratio also shortens the elements. There's no dielectric involved, so there's no velocity factor (except for air).

See the NEC2 deck below. Note that the element lengths are 0.1814 wavelengths per side, not 0.25 wavelengths.

This is why you want a VSWR bridge and sweeper. You can see the resonant frequency (i.e. cut-n-try).

It's more rigid and stable. See:

this method.

However, the problem with all of these is that remarkably few have done any manner of VSWR or gain testing. Yet, they still work because the antenna is sufficiently broadband to tolerate some miscutting.

the VWSR graph.

CM NEC Input File Biquad for 2439 MHz, Pow 20020608 | CM All data in wavelengths. Scaled to meters with GS | CM --------------------------[

]--' CE SY A = .1814 ' Element dimensions SY B = A * 2 ' SY R = .006 ' Wire radius SY L = R + .001 ' Gap for soldering to feed SY H = .132 ' Element height over reflector SY RX = .500 ' Reflector vertical length / 2 SY RY = .600 ' Reflector horizontal length / 2 SY RH = .230 ' Height of reflector sides GW 1 10 H .0 L H A A R GW 2 10 H A A H B .0 R GX 1 011 GW 9 1 H .0 -L H .0 L R SM 12 10 .0 -RY -RX .0 RY -RX SC 0 0 .0 RY RX SM 12 3 .0 -RY RX .0 RY RX SC 0 0 RH RY RX SM 3 12 .0 -RY -RX RH -RY -RX SC 0 0 RH RY -RX GS 0 0 .123 GE 0 FR 0 1 0 0 2439. 0 EX 0 9 1 0 1. 0 RP 0 73 73 1001 -90. 90. 5. 5. 10000. EN

Marty seems to be doing the using wire, not pipe.

I'd like to build one of these antennas for the 1.7Ghz federal band. At that frequency, I have radios that can be used to determine signal strength. Would sweeping the antenna by hand and checking the S meter be sufficient to determine a match?

snipped-for-privacy@sushi.com hath wroth:

You want to do the driven element with 1.5" pipe at 2.4GHz? No way. It's too short a wavelength and too fat a pipe. I don't see what you're trying to do (or how you plan to do it).

If you're thinking of building an indoor antenna range for gain testing, forget it. The reflections and nearby metal will be impossible to control. Retest the next day and you'll get completely different numbers.

I have a handy 2.4Ghz antenna range in that I have line of sight to Loma Prieta, where several WISP's have their access points. I go outside, point the antenna at the mountain, and measure the receive signal strength on either a spectrum analyzer or Wi-Fi client radio. I then compare it with my reference antenna (which seems to be hiding somewhere). I know the exact gain of the reference antenna and use the DIFFERENCE to establish the actual gain. I've tried to do antenna patterns by rotating the antenna, but the signals from Loma are not strong enough to use effectively.

Nope. If you're dilligent and build a graph of frequency versus VSWR, you might obtain something useful. However, hand sweeping is tedious, and difficult to use effectively. You really, really, really, really, need a sweep generator and a scope (or computah display) in order to tweak anything you build.

I'll post some photos. I was going to do it yesterday, but I got busy on the roof, and then a big electrolytic blew in the sweeper. Such is life with old test equipment.

Use a pipe cutter on the 1.5 inch pipe and cut off a sliver off the pipe. This will form the ring to be used as the antenna. You can cut this ring then trim it it to the right length. The idea here is the shape will be close to what you need. Not on the money mind you, but close enough to adjust.

snipped-for-privacy@sushi.com hath wroth:

Yeah, that might work except for a few problems.

- Copper pipe is rather hard and somewhat brittle. It's going to be difficult to bend to shape.

- Cutting a thin piece of pipe with anything other than a cutoff tool in a lathe is going to be difficult. You're likely to crush it with a pipe cuttter or hack saw.

- Asymmetrical cross sections work just fine, but do not result in the same cut length as a circular cross section.

- Mechanical stability is slightly better than using copper wire, but not by much.

- I don't like sharp corners.

- You can get the same results with copper roofing flashing and a pair of tin snips. Roofing flashing is also not as hard or brittle as copper pipe.

Ah, but it is nearly in the right shape since the pipe diameter was picked to be close to the target. You want it to be difficult to bend because you want to maintain the initial shape.

This I don't follow.

I think the pipe would be more stable since the copper is rigid.

Me neither. An antenna using copper pipe for the driven element would be suitable for a frat house branding tool, or to persuade Gitmo prisoners to talk.

I'll look into this, but tin snips generally curl the edge. Harbor Freight, importer of crappy made in China tools, has a mini-shear.

paid the local store a visit, inhaling the fumes of what must be metal preservative for the long trip from China, only to find they don't have this shear in stock. I was hoping it would cut PCB. I did pick up some $3.99 DVMs.