[600MRG] modified MFJ Antenna analyzer failure

Thu Mar 21 11:59:17 CDT 2013

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
>_______________________________________________
>600MRG mailing list
>600MRG at w7ekb.com
>http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com

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