[600MRG] modified MFJ Antenna analyzer failure

[Edward R Cole]

John,

It took about 6-weeks for my MFJ meter to be repaired....sooo

You have convinced me to obtain the diodes from MFJ.  I already have 
the schematic from back when it was repaired (I bought the meter used 
on e-bay and it ran about 5-days). Having the direct contact number 
for the technician will help if more work is needed beyond 
replacement of the diodes.  Removal of chip diodes it not too hard 
using two solder irons.  The MFJ pc board does not appear to be 
durable for much repair work so my trepidations, though experienced 
sm tech...maybe because I am experienced :-)

It would be quicker to try self repair than the trouble to remove my 
mods and then re-install them.

73, Ed - KL7UW
BTW I had a commercial BC antenna bridge that would tune with 5kW 
applied.  But I discovered it cost $7K purchased new and was able to 
sell it for $2K (buys a lot of ham goodies).  These were typically 
permanently installed at the transmitting antenna so that impedance 
could be measured at any time. It had 7/16 coax connectors and came 
with adaptors to N for testing.

At 11:10 AM 3/21/2013, John Langridge wrote:
>Warren,
>
>yeah, no good at all.   One station I know is 4 miles west of me and he has a
>bad time with the 50kw it seems.  I am VERY fortunate at this 
>location.  Most of
>our AM's are located north 15-20 miles...
>
>As an update, MFJ is quoting 3-4 weeks turn around.  Whether it is 
>really that
>bad or just a worst case quote, is anyone's guess.  As Ed indicated, 
>$70-80 is
>what was quoted.  MFJ will sell the parts and provide detailed schematics and
>those parts would be here in 3-5 days but I have not asked how much - I would
>not expect it to be too much.  I suspect i will do the latter first and if I
>somehow fail, I can always send it to them.
>
>In the interim, one option that can utilize parts I have on hand was done by
>GW3UEP, whose designs I use for my amps:
>  http://www.gw3uep.ukfsn.org/TestGear/QRPMeter/qrpmeter.htm .  I 
> suppose this is
>better than nothing for a temporary solution.
>
>73,
>
>John /NJD/XIQ
>
>
>
>
>
>
>________________________________
>From: Warren K2ORS <k2ors at verizon.net>
>To: 600mrg at w7ekb.com
>Sent: Thu, March 21, 2013 1:37:47 PM
>Subject: Re: [600MRG] modified MFJ Antenna analyzer failure
>
>John,
>        You are very lucky that you have only one 50kW AM transmitter and
>it is 20 miles away. I have 4 50kW and one 40kW transmitter within a
>dozen miles of here.
>
>73 Warren K2ORS
>
>
>On 3/21/2013 12:59 PM, John Langridge wrote:
> > Ed,
> >
> > Thanks again!  Just as I sent my message to the list, I received 
> the following
> > response from MFJ so I will be giving them a call:
> >
> > "must be the schottky diodes d1-d4 then.  those are 2820 surface mounts.
> > call jimmie allen, analyzer repair technician, 1-800-647-8324 or
>1-662-323-0549
> > for more information."
> >
> > As you say, $70-80 is not bad for a $400 unit unless this happens every 6
> > months.. really not sure what happened as nothing was different 
> from a normal
> > session.  Its been more humid so static is not what it had been 
> and no storms
> > were around... who knows?
> >
> > Anyway, at my QTH I've never had any problems with BCI even with 
> a 50kw around
> > 20 miles west of me.  Interestingly, the FM's and TV's 5 miles south of me
>seem
> > to cause most people around here the greatest problems, but its 
> never been an
> > issues for me.
> >
> > 73 and thanks again!
> >
> > John /NJD/XIQ
> >
> >
> >
> >
> > ________________________________
> > From: Edward R Cole <kl7uw at acsalaska.net>
> > To: John Langridge <jlangridge at sbcglobal.net>; 600m research group
> > <600mrg at w7ekb.com>
> > Sent: Thu, March 21, 2013 11:43:43 AM
> > Subject: Re: [600MRG] modified MFJ Antenna analyzer failure
> >
> > John,
> >
> > Coincidentally, I blew the front-end of my MFJ-269B.  I was checking
> > the match of a HB coax switch matrix and 26vdc was applied to the MFJ
> > antenna.  They specifically warn against applying any dc
> > voltage.  There are diodes in the ckt that probably are gone.  I
> > debated fixing it myself but decided the possible pcb damage from
> > removing surface-mount devices made factory repair a better
> > choice.  I wrote them a month ago and here is the reply:
> > ------------
> > Subject: Re: Repair of MFJ-269B
> > From: mfjcustserv at mfjenterprises.com
> > To: "Edward R Cole" <kl7uw at acsalaska.net>
> >
> > we now say $70-$85 parts, labor and return shipping just to cover
> > us.  thanks for your business.
> > ----------------
> > Considering it is nearly $400 new that seems reasonable.  I have used
> > MFJ repair once before on this meter (for another issue).  I plan to
> > remove the modifications before shipping and add a note not to repair
> > the 4-MHz oscillator selection as I will be re-installing my mods.
> >
> > Use of the antenna analyzer is subject to strong BC signals so it is
> > limited where this is not a problem.  I have one nearby station about
> > 16-miles south of me on 920-KHz.  There are stations on 550, 600, and
> > 750 KHz in Anchorage 65 miles NE but they are not strong enough to
> > confuse my measurements.
> >
> > 73, Ed - KL7UW
> >
> > At 05:05 AM 3/21/2013, John Langridge wrote:
> >> Hey guys,
> >>
> >> At my station, part of my SOP is to adjust my antenna system before
> >> and during a
> >> session using my modified MFJ259B.  The mod is the one detailed by
> >> KL7UW and I
> >> have found that its measurements are "in the ball park" compared to known
> >> accurate meters that I have borrowed in the past.  Last night, I had
> >> a failure
> >> with my analyzer and it has been suggested that the detector has finally
> >> popped.  50 ohms loads are now 39 ohms and reactance changes very
> >> little from 0
> >> even when I know it is much higher.  I have always been very 
> careful to make
> >> sure the analyzer is not connected to anything when transmitting 
> and that was
> >> the case again last night.  I am hoping someone knows a solution to
> >> this problem
> >> short of sending the box back to MFJ.  I suspect my mods, which are
> >> all crammed
> >> inside the chassis, will get wrecked during repair or they may not
> >> even want to
> >> work on it given it has been modified.
> >>
> >>
> >> While I try to find a solution, I am wondering what methods you guys
> >> are using
> >> to ensure a match.  How do you know in a pinch that its 50 ohms 
> at the feed
> >> point or do you worry about it?  I think we can all agree that a
> >> matched system
> >> works best and given my low grant ERP, I don't want to waste
> >> anything and think
> >> that careful attention has contributed to my success thus far. Minor
> >> variations
> >> probably do not matter too much and the data supports that fact and
> >> my FETs and
> >> current limited power supply have never blown apart as the result of
> >> an untimely
> >> mismatch but I exercise an overabundance of caution so I am not 
> experiencing
> >> downtime on a regular basis.  I have been pleasantly surprised at
> >> just how much
> >> abuse the FET's I use can take, however.
> >>
> >>
> >> Here are a few of my options as I see it:
> >>
> >> I can used the remote control variometer to peak antenna current 
> and I know
> >> where it should be but I also have seasonal variations due to foliage.
> >>
> >> I know about how much current my PA draws for a given voltage when
> >> everything is
> >> working.
> >>
> >> I probably have a forward power meter that will allow me to peak 
> the output
> >> using the variometer, perhaps peaking that in conjunction with the base
> >> current.  Accuracy would not be important on the meter but it 
> may change the
> >> system when I take it out of line (it shouldn't but I've seen it
> >> happen before).
> >>
> >>
> >> long term I need to look a mod for an SWR meter.  There was one
> >> floating around
> >> at one point for a simple heathkit meter mod.  anyone have the pdf
> >> or a link for
> >> it?  I have looked for it in the past but never found it and admit
> >> its probably
> >> right in front of my nose.
> >>
> >> I hear good things about the scope match option.
> >>
> >> adding a motorized coil to my shunt match would allow me to handle minor
> >> seasonal or weather-driven variations...all of these are 
> something to think
> >> about in the future...
> >>
> >> Any additional ideas or guidance would be appreciated.
> >>
> >> thanks!
> >>
> >> John KB5NJD/WG2XIQ
> >> _______________________________________________
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> >
> >
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>
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