Re: Looking for pc card with better reception

On Aug 4, 2004, at 5:38 AM, Haudy Kazemi wrote:

> There are also 300 mW (24.8 dBm) prism 2.5 cards from Demarctech.  I
> haven't tried them but the specs are here:
> http://www.demarctech.com/products/reliawave-rwz/reliawave-rwz-300mw- 
> prism2
> -5-pcmcia-card.html
> http://www.demarctech.com/techsupport/rw-wireless-cards-support/100mw- 
> rx-te
> st.htm
>
> Their 100mw and 200mw models sensitivity was found to be, and the 300mw
> card is probably about the same:
> -91dBm  11mbps FER<8%
> -93dBm 5.5mbps FER<8%
> -95dBm   2mbps FER<8%
> -96dBm   1mbps FER<8%

Theoretical receive sensitivity can be calculated as:

Receive sensitivity = Nt + Ns + SNRmin

where  Nt is the thermal noise floor,  Ns is the system noise figure,  
and SNRmin is the minimum SNR required for a given bit-error rate.

802.11b's CCK requires a SNR of about 10dB to decode frames with a FER  
of 0.08. (We'll leave SIR and/or SINR out of the discussion unless  
someone insists.)  We'll call this SNRmin.

All matter at temperatures above absolute zero (0K, about -460F)  
radiates electromagnetic energy. The amount of energy is related to  
temperature -- the hotter the matter, the more energy is radiated. This  
energy is described by Boltzmann's Constant, 'k' (k =  
-198.6dBm/degreesK-Hz). This constant, multiplied by the temperature of  
the matter a receiver views and the system bandwidth, yields an  
irreducible background noise against which a desired signal must  
compete. This is thermal noise.

For the purpose of this exercise, lets use 80F, or about 300K (T=300K).  
RF engineers typically use this number as a rule of thumb, and its  
roughly the year-round temp here in Hawaii.  :-)

802.11b uses a channel 22Mhz wide.

Tn(dBm) = -198.6 + 10 * log10(300) + 10 * log10(22,000,000)  =  
-100.4dBm.

Receive sensitivity = Nt + Ns + 10log(BW) + SNRmin
                   -91dBm  = -100.4dBm + Ns + 10dB

You can see we're in-trouble already.  (Or my math is out to lunch, and  
someone will correct me.)

The thermal noise floor is at -100.4dBm, we require 10dBm of SNR, and  
someone has promised us -91dBm rx sensitivity.    Even with a  
noise-free (perfect) LNA and receiver chain, we're slightly short.

I'll leave it as an exercise to the reader to fill in the noise figure  
for the LNA and Prism-II receiver on the Zcom designs.  They'll be  
listed on the datasheet(s) for the part(s).

> That said, the extra power may or may not make a difference in your  
> ability
> to talk to an access point, depending on the AP's own sensitivity.   
> (If you
> have a powerful but insensitive AP, this card may help.)
>
> Note: there was a way to overdrive the 200mw Senao cards to 249mw  
> using one
> of the linux drivers.

Its a huge mistake to do this, and not just for the obvious legal  
reason.

> Maybe the 300mw cards can go even higher...or maybe
> like when overclocking cpus, the higher spec chips are simply the  
> higher
> grade cut of the chip production line.

This is what Tony would like you to believe, but its not true.

3054 is 21dBm in 11b modes.  (+/- 2dBm)

>
> Aries info links:
> review: http://ben.pfountz.com/~bpfountz/3054CB.html
> http://www.netgate.com/3054CBARIES.html
> http://www.netgate.com/New/NL_3054%20CB%20Aries.pdf
> http://www.hautespot.net/products/datasheets/nl-3054%20cb%20plus- 
> spec.pdf
> Atheros AR5212 baseband, AR2112 radio
> Typical TX Output power upto 21dBm / 126mW
>
> On 4 Aug 2004, crispin wrote:
>>     The Senao cards are some of the best, check out netgate.com for
>> descriptions.  They are available with or w/o buit-in antennas.  Until
>> recently they were among the highest powered "B" cards w/200mw of
>> power(compared to an Orinoco or mant other at about 32mw), they have
> great
>> sensitivity as well.  They also use a standard Prism chipset so they  
>> play
>> well w/other gear.  You should be able to pick one up for around  
>> $70(just
>> saw that they're on sale @ netgate for $65).  That site also has a  
>> good
> "G"
>> card based upon the Atheros chipset, the Aries, which is 100mw(high  
>> for a
>> "G" card").  They also have the same cards available in a mini pci  
>> form,
>> enjoy.  crispin
>>
>>
>> On 8/3/04 2:59 PM, "Philip J Robar" <[email protected]>  
>> wrote:
>>
>>> On Aug 3, 2004, at 1:36 PM, Randy S wrote:
>>>
>>>> I'm looking for an 802.1b, g is optional, ext. antenna jack is
>>>> optional, pc card that has great reception with just the built in
>>>> antenna.
>>>>
>>>> Can anyone recommend a good card or a good site with some tests and
>>>> reviews of hardware? I'd like to upgrade from my current Netgear
>>>> MA401.
>>>
>>> http://www.practicallynetworked.com
>>>
>>> Phil
>>>
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