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56ww Profile
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DX-pert

Registered: 08-2009
Posts: 722
Karma: 6 (+6/-0)
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posticon s units and db


hi to all
here i find some rules how s units means by db or power
 

S-meter standard readings as defined by IARU. One S-point is equals to a signal difference of 6 dB. The value in microvolt is given into 50W. On frequencies below 30 MHz, a S-9 signal is equivalent to a power of -73 dBm
 

http://www.astrosurf.com/luxorion/qsl-db-power-units.htm

if u think u got to lift your signal from 56 to 59, then you must give 3db+3db+3db+3db+3db+3b more and 3db is double power, so if 10wats give s6 units. to s9 units, u need 10+10+10+10+10+10 wats more to s9 signal. ok, thats not bad whit qrp power, but think if u have 100 wats to s6 and u will to lift it up to s9, then u have problem, but let see this from backside. u got s9 signal whit 100w then you can drop the power to 50w and only half s units go down.
best way to better signal is good antenna and that can give more s units from received signals also.
73'mike
my mathematic is bad like my english, but its near enough.


Last edited by 56ww, 5/Jan/2010, 9:56 pm
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John193 Profile
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Freebander

Registered: 11-2008
Location: South Glos
Posts: 260
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Re: s units and db


Unfortunately your "S" meter isnt linear its LOG. so 3dB at S1 is not 3dB at S9. If only!.
It is also NOT calibrated by any stretch, so its a relative sig level only and its different on every radio. ie its for comparative use only.
-73dB S9 is measured from a sig generator output (minus the patch lead loss)and doesnt have any bearing on coaxial loss antenna gain etc. Finally the test signal is at max bandwith for that mode ie 2.8k or3.0k,and as I'm sure you're aware if you narrow the bandpass the sig strength drops to but the s/n goes up generally. In a nutshell its like measuring watts with a meter verses a calorifier, its no contest. Its there just for relative comparison only.
John193
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rich 26fb456 Profile
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Registered: 07-2009
Posts: 124
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posticon Re: s units and db


 hi john! good point! i have always wondered why the rig manufactures can not come up with something between them! that reads the same! on rx scale! it could be so easy and mean something as well!! then again as you say filters play a big part in rx signal that would mean they would have to have the same front ends as each other!! or very close!! maybe they could all combine and call it yae ken com 73s. emoticon
12/Jan/2010, 11:54 am Link to this post Send Email to rich 26fb456   Send PM to rich 26fb456
 
56ww Profile
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DX-pert

Registered: 08-2009
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posticon Re: s units and db


hi gents, thats right. most important is that you can hear stations and have a qso. but there is not so much big deal if you use 150w or 55w if your qso mate read you s9+ (if qrm/n is less than s2-3), 73'mike
12/Jan/2010, 12:37 pm Link to this post Send Email to 56ww   Send PM to 56ww
 
56ww Profile
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DX-pert

Registered: 08-2009
Posts: 722
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posticon Re: s units and db


Hi Jhon and Rich,
this is litlle off topic, but what u thinking about band pass filtters, homemades. rx front ends in cb radio is quite wide, 23to34mhz i guess, maybe more?? but whit ham rigs have same kind probs also. This can help whit qrm/n and harmonics and make cleaner signals to radio what can handlle it easyer (prosessing)
So whats your opinion about that.
73´mike
ps, if use whole ham bands then u need more of them, or using commercial auto tune bpfilter
12/Jan/2010, 2:08 pm Link to this post Send Email to 56ww   Send PM to 56ww
 
26fb139 Profile
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DX-pert

Registered: 01-2008
Location: Dudley west mids
Posts: 1275
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Re: s units and db


a single band pass filter will not only filter it's freq but its harmonics ie
7mhz but 14 21 28 etc
so different filters are fitted for tx & for rx.
if you are getting a tvi problem get a bandpass filter for ya rig & a filter for the back of the tv.
 emoticon

---
139 in any GOOD group??
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rich 26fb456 Profile
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Registered: 07-2009
Posts: 124
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posticon Re: s units and db


hi mike! happy new year to you!! i know the ham rigs have filters in to help stop interference! they usually have one for each band your on! same as some amps!! i made one many years ago as a colledge project! for cb band! as you can guess that didnt go down to well!!!

i will have to try and find it! most things are quite easy to make now a days what with the internet! theres nothing you cannot find!! i have seen low pass filters on the net!!! it would probably cost you more to make one than by one!! now a days ! 73s rich.
13/Jan/2010, 7:15 pm Link to this post Send Email to rich 26fb456   Send PM to rich 26fb456
 


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