> To: RHealy@mdsroc.com, topband@contesting.com
> From: km1h@juno.com (km1h @ juno.com)
> Subject: Re: TopBand: Followup Beverage Box
To: <amps@contesting.com>
> Date: Thu, 18 Sep 97 00:01:25 +0000
My experience agrees with Carls.
> Hi Russ;
> I agree except the MAV-11 is no more destruction proof than the MAR-3. It
> does have better IMD and NF specs but both are rated at the same +20dBm
> maximum input level. The MAV-11 is used in the DEM 6M xvtr as a mixer
> post-amp.
I'd like to add something I have observed building post amps and
pre amps in broad band systems. The MAR series of amps are VERY IMD
prone in broadband circuits. It's true the one dB compression points
are high, but the MAR series of MMIC make horrid amps in the presence
of broadband signals since the harmonic distortion levels are high
even IF you are not saturating the device.
A single LT1001 or cheap 2N5109 is much more immune to damage, has
better IMD performance, and a better noise figure. MMIC's are simple
to use, but that does not make them good devices.
As a matter of fact, I tried to use the MAV-11 in an antenna analyzer
and the harmonic content of the output was totally unacceptable.
Even with nearly 100 mA of bias current, its harmonic distortion was
twenty dB worse than a single 2N5109 with 40 mA quiescent current!
Why run more current to get poorer performance since the only
advantage is saving a few components? With two 2N5109's in push pull
with transformer feedback, the one dB compression point is over ONE
WATT, the noise figure is under two dB, and the thing will take ten
watts of input pulse without damage.
> Another potential weak link is the MCL T9-1 transformer...its
> subminiature size makes it a good candidate for getting zapped.
....and also makes it prone to overload. I substituted MCL
transformers in a push pull preamp and what was a VERY clean amp
became overloaded with BC birdies. Be aware that almost ANY
amount of current in the windings will saturate the tiny tiny cores
in these transformers.
> While the ZJ box is a good lab concept, it just may not be the proper
> choice for those in somewhat hostile enviroments. Replacing pilot light
> fuses every few minutes during a blizzard is not my idea of protection
> especially if the box is 700' away. Why on earth anyone would want a
> remote preamp on 160/80is also questioned.
Amen Carl. Even at the quietest location, a Beverages noise will
greatly exceed cable losses. Install the cable properly, using
reasonably good feedline (CATV drop line is excellent) and GOOD
connections at the connectors, and the preamp might as well be right
next to the receiver.
73, Tom W8JI
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