w8jitom@postoffice.worldnet.att.net wrote:
snip......
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.
Hi Tom,The ZJ boxes I have are not broad band. They are either single-band, or
1.8-4.0 mhz.
The tuned circuits in the pre amp are very good, as a 50kw AM station 4 miles
away
cannot be heard at all on my EWE.
>
>
> 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.
I have no idea why they chose these devices in such a hostile environment.There
must be some advantages.
> > 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.
Because we are all not so fortunate as to have beverages. A lot of us
citydwellers are running EWE's, and need the pre amp. In my case, the utilities
are all underground and even using 9913 coax, there was 60hz pickup in the
shack mounted pre amp which was amplified along with the signals. By putting
the pre amp at the EWE and adding a line isolator at the ZJ box output to keep
the
60hz out of the ZJ box, all noise was eliminated.
>
>
> 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
See above....not in ALL cases!
(((73)))
Phil, K5PC
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