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Message-ID: <3.0.1.16.20010425103123.3097901e@mail.cc.kuleuven.ac.be>
Date: Wed, 25 Apr 2001 10:31:23
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: Pre-amps.
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I forgot to list Mini-Circuits's new monolithic amps, these have even
better IM behaviour :
type	gain (dB)	noise fig. (dB)		3rd order IP (dBm)
GAL-4	14		4			+34
GAL-5	21		4			+35
GAL-51	18		4			+35
GAL-6	12		5			+36

73, Rik  ON7YD

At 09:43 25/04/01, you wrote:
>Hello Laurie,
>
>In most circumstances SNR will be determined by the 'band noise' (QRM -
>QRN), so the noise figure of a pre-amp won't matter too much (anything
>below 10dB should be fine). But, unless you have a very small antenna in
>combination with a very 'deaf' receiver a pre-amp won't be of any use, it
>will just crick-up the S-meter reading but will not improve readability of
>a signal.
>
>I did some tests woith pre-amps and found out that most simple designs have
>a too poor IM behaviour and make things worse instead of better. If I would
>design one I would primarily aim at a high IM rejection and don't worry too
>much about noise figure or gain.
>If you want to use one of the monolithic amps from Mini-Circuits I would go
>for something better than a MAR-6, that one has the worst IM behaviour of
all.
>To compare :
>
>type	gain (dB)	noise fig. (dB)		3rd order IP (dBm)
>MAR-6	20		3			+15
>MAR-8	33		3			+27
>MAR-4	8		4			+26
>MAR-3	13		6			+23
>ERA-1	12		7			+26
>ERA-2	16		6			+27
>ERA-3	22		5			+23
>
>Personnaly I wouldn't recommend the ERA-8 as it tends to be unstable in non
>resistive loads, but I would go for a ERA-2.
>Price of all these amps is very similar (MC suggested resale price at 30
>QTY is between 1 and 2 USD for all of them) and mainly depends on what your
>local supplier stocks (and how greedy he is .... ..).
>
>An old wisdom, but still valid : the best RX amplifier is a good antenna
>(0dB noise figure and almost endless IP3).
>
>73, Rik  ON7YD
>
>At 18:41 24/04/01 +0100, you wrote:
>>Hi All,
>>I have been thinking about weak signals on 136 using QRS and DFCW. These
>techniques enable signals to be read which are buried 30db down in the
>noise(see Extreme narrow bandwidth techniques ON7YD ) Does this mean that
>signals 30db down on atmospheric noise are seen,if so what about the noise
>from the RX pre-amp ? In my case this is about 20/30 db less than the Ant.
>noise,so would I be looking at the pre-amp noise or is this also reduced by
>the narrow bandwidth ?
>>I should like to improve the noise performance of my pre-amp.
>>filter combination. and would appreciate any information on high
>performance circuits or amp. units. Is the MAR6 likely to be worth while.  
>>By the way if my thoughts are correct this may be why high Q loops are
>reported to be superior to lower Q types, higher signal output overriding
>amp. noise. Any ideas ?      73s  Laurie.  
>>
>>Attachment Converted: "C:\EUDORA\ATTACH\LFPre-am.htm"
>>
>
>