At 04:47 PM 11/5/97 -0500, you wrote:
>I wrote ZJ, which a month later sent me a replacement device, gratis.
I sent my box back in, and it was repaired gratis...also took >month.
>My ZJ Box did not come with a schematic which is my main complaint.
Mine also. It is much faster to be able to repair it myself.
>I agree that it is an odd choice, but my Avantek Semiconductor Data Book
>shows that the power gain and other MMIC specs are flat from about 0.1 to
>about 1 or 2 GHz, depending on the specific device. Also, the Avantek power
>gain versus frequency chart shows them being flat to DC! Therefore, the
>device should be suitable for 1.8 Mhz.
These devices work fine at 1.8 mhz, as advertized. I experience none of
the overload problems eluded to in earlier posts. The B.C. band filter
is super! I have a 50kw B.C. station 4 miles away (WBAP, 820khz) and when
my RX is tuned to that freq., I can detect no signal at all! Also the
way the box mounts directly to the ground rod is nifty. Yes Virginia,
some of us small-lot city dwellers do not have room for beverages, and
we need the preamp for use with EWE's and other compromise antennas.
My EWE and the ZJ box have allowed several very rare DX QSO's on both
80 and 160 meters which would not have been possible otherwise. The
preamp being at the antenna gives me a better S/N ratio, as I have
all underground utilities in my neighborhood, and the EWE is only 5 feet
from a transformer.
I had previously described the fix I used to protect my ZJ box by installing a
miniature pilot lamp between the antenna binding post and the RF input to the
board. It has taken this long to prove its worth, but I finally had a failure
this week. There was no weather in the area, so the "hit" was from either my
80 meter or 160 meter verticals, which are only 15-20 feet from the EWE. The
hit was so hard that it turned the inside of the bulb totally black and
vaporized the filament. The MMIC and transformer came out unscathed! I
replaced
the lamp and put the EWE back in service. It takes 35 cents and 5 minutes to
add a major protection for the box. I highly recommend the ZJ products(with
the
mod.)
(((73)))
Phil, K5PC
> KM1H siad there had been a discussion of the ZJ Beverage Box which can
>be found in the archives. So more information is available there. He also
>said that the ZJ Boxes had been shipped with "at least 4 different" MMICS
>including the MAR1, MAR3, and others. He stated that some of those devices
>needed different biasing. He also stated the ZJ Box was subject to overload
>and IMD. Carl said the "ultraminature 9:1 balun is just as bad."
>W8JI suggested replacing the MMIC with "a regular CATV transistor."
> W4MPY wrote that his ZJ beverage box filled up with water and that he
>has tried unsuccessfully to get help from ZJ.
> Both W8JI and KM1H stated that a good beverage will not generally need
>a preamplifier.
> K0CS kindly sent me a MAR-3 device which had been supplied by ZJ as a
>replacement device.
> Looking at the various Avantek MMIC specs (I can not find my cross
>reference to compare the Avantek MSA MMICs to the MAR MMICS) I see several
>MMICs with very similar specs (in some cases just different plastic packages-
>ie. cases). Almost all of them require 4.5 to 5.5 volts DC. I suspect the
>several different MMICs supplied in the ZJ boxes have identical specs at 1.8
>MHz and that biasing is not an issue. For those who need to replace the
>MMIC, a MAR-1, MAR-3 or equivalent should work fine. MMICs are listed in
>several of my electronic catalogs for about a dollar each.
> I hope the above is useful information and that some of you get your ZJ
>beverage boxes back up and running. Unfortuately, mine still is not working
>after I replaced the MMIC. I suspect that the ultraminature balun, as KM1H
>described it, needs replacement. Not sure I want to proceed until I get a
>schematic. Does anyonwe have one?
>See also my next post on beverage transformers.
>Doug W0AH
>
>
>
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>
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