[Premium-Rx] Mini-circuit amps

[Karl-Arne Markström]

A word of advice regarding the ZFL-series and similar amplifiers.

They are single-ended, so their IM2 performance is much worse than most
receivers having sub-octave preselection. 

My experience, earned the hard way, is that it takes a balanced amplifier like the AM-109, 
the HELA-10 or the circuit used in the R&S NV14 multicoupler to properly handle the output signals from a 
multi-octave gain antenna like a log-periodic or a rhombic.Amplifiers of the ZFL class connected directly to 
a large log-periodic convert the European HF spectrum to a mess of mixing products even in the best of "Prem-RX's".

If the input spectrum is limited, the situation becomes much better.

A 10 or 12 dB attenuator before the amplifier would result in a multicoupler with a gain of 2 to 0 dB, 
an IM3 dynamic range of about 85 dB when connected before a typical HF receiver,
and it would degrade the noise figure of a 10 dB NF receiver to about 16 dB. 

This would be sufficient on HF for all but the smallest antennas, but the potential IM2 problems would still be there.

To calculate this, I have used the program "NoiseCalc" in the freeware software package "AppCAD" from HP/Agilent.
It is recommended.

73/

Karl-Arne
SM0AOM







----- Original Message ----- 
From: <Ka9p at aol.com>
To: <premium-rx at ml.skirrow.org>
Sent: Sunday, November 13, 2005 3:42 AM
Subject: [Premium-Rx] Mini-circuit amps


> I'm getting ready to fiddle with a MIni-Circuits ZFL-500LN amp ahead of a 12 
> way splitter to use as a poor man's multicoupler.  Because it was all cheap :)
> 
> The amp has nominally 20 - 25 db gain or so, which I'd like to reduce to make 
> the system a unity gain set up.  Can anyone hazard a guess what the best 
> approach to doing this might be?  I've considered an attenuator on the output of 
> the amp, but was also curious whether the gain might be usefully varied by 
> reducing the supply voltage, and what effect that might have on noise figure 
> (which is OK at less than 3db) or 3rd order IMD (which ain't very good already at 
> about +14 db).
> 
> Thanks for any ideas.
> 
> Scott
> 


--------------------------------------------------------------------------------


> _______________________________________________
> 
> Premium-Rx Mailing List
> To Post: premium-rx at ml.skirrow.org
> For Info: http://ml.islandnet.com/mailman/listinfo/premium-rx
> Visit the Website: http://kahuna.sdsu.edu/~mechtron/PremRxPage/
> 


--------------------------------------------------------------------------------


No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.1.362 / Virus Database: 267.13.0/167 - Release Date: 2005-11-11



-- 
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.362 / Virus Database: 267.13.0/167 - Release Date: 2005-11-11