On Wed, 5 Nov 1997 17:25:05 -0600 philk5pc@connect.net (Phil Clements)
writes:
>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.
A competent tech can copy that circuit in 10 minutes and generate a
schematic. There are only 20 components on the PC board and 12 of them
are the filter.
>>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.
Very true and the antenna signal levels are much lower than on a long
Beverage. After all it is sold as a Beverage Box...not a EWE box; at
least in the literature I have here.
At this QTH I am surrounded with 5KW BC stations in the 3 to 10 mile
range and most of them are above 1400KHz. The IMD generated in all of the
ZJ boxes repaired here make 160M useless for weak signal DXing. Perhaps
if I were to build a BC filter properly matched to the ZJ input impedence
it would help.
The ZJ filter is after the 9:1 xfmr and before the MMIC. The 9:1 xfmr has
both input and output windings to a common ground and all other grounds (
filter, DC bypass, etc) are also common on the PC board. This is asking
for ground loop problems. As mentioned here previously by many others
that is a poor way to operate a Beverage.
I have another ZJ box here for repair that I have not even opened the
shipping box yet.
I'll be glad to run some tests....any suggestions?
I have found an old Palomar 3N204 tuneable preamp to have an extremely
high Q on 160/80M and a big help in even eliminating in-band IMD on my
conventional Beverages. The bandwidth is about 10KHz and I set the gain
for minimum...about 5dB.
73 Carl KM1H
> 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
>>
>>
>>
>>--
>>FAQ on WWW: http://www.contesting.com/topband.html
>>Submissions: topband@contesting.com
>>Administrative requests: topband-REQUEST@contesting.com
>>Problems: owner-topband@contesting.com
>>
>
>--
>FAQ on WWW: http://www.contesting.com/topband.html
>Submissions: topband@contesting.com
>Administrative requests: topband-REQUEST@contesting.com
>Problems: owner-topband@contesting.com
>
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
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