| K6BRN |
Rating:  |
2023-01-30 | |
| Usual MFJ Problems |
Time Owned: more than 12 months. |
The MFJ-854 is a device for inductively indicating the presence of RF current on the shield of a coax cable or in a lone wire. I say "indicating" because it does not seem to be particularly accurate, in my experience with TWO of them. However, this meter IS useful for comparative and "getting warmer/getting colder" type of non-demanding RFI/EMI testing. Sometimes that's all that's needed.
One of the two examples I've used had its sensitivity control pot miswired, causing it to operate the opposite way the instructions indicated and the opposite of the other meter. I recommend that anybody buying one of these new open it up and let the solder balls drop out, THEN check all solder joints for integrity. SOP for MFJ stuff, in my experience.
That said, I did drop one of them from a height of about 16 feet, whereupon it glanced off the side of a concrete wall and hit a sidewalk. Still worked about as well afterwards as it did originally. so at least the case is pretty tough!
Can be useful but likely to need some sorting after purchase and realization by the operator that it's absolute accuracy is usually low - try comparing two of them side by side for some amusement. Not really an "instrument". More of a "Divining Rod" for detecting RF currents.
But it's pretty inexpensive (and you get what you pay for).
Brian - K6BRN
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| N8RAT |
Rating:  |
2023-01-29 | |
| Total Junk |
Time Owned: 0 to 3 months. |
The meter just flops around inside the case. There appears to be nothing to hold it in place. The power switch was non-functional. Had to fabricate a replacement to get it to power on. Once I was able to power up, operation was intermittent until I repaired several bad/cold solder joints. The sense coil is held in place with a white zip tie. Are you kidding me? It looks like a six-year-old assembled it as a science fair project. The only acceptable thing about it was the box in which it was shipped. I suggest anyone interested in buying one purchase the optional “works out of the box” feature.
This is the last MFJ product I will EVER buy.
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| KC1LML |
Rating: |
2023-01-23 | |
| Works as expected |
Time Owned: 0 to 3 months. |
Works fine, but does seem a bit over-priced. Yes, the clamp is almost impossible to open, unless you are mechanically inclined and take the time to examine it. Once you see how and where it flexes, it can be opened in a split-second every time.
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| VA7MMW |
Rating: |
2020-03-06 | |
| Lives up to reputation |
Time Owned: 0 to 3 months. |
This is the first MFJ product I've bought. I was hesitant given the reviews for this particular meter, and those for MFJ's other products. The saddest thing about this product is that it could be reasonably good if a minimum of effort had been put into quality control.
One has to open the unit up to install the battery. The 9V battery holder had two holes in it, with two matching holes in the case. Instead of being fastening to the case using rivets, the battery holder was double-sided foam taped to the chassis. Odd. When I tried to install the battery, realized that it was impossible to close the case with the battery installed. This is because there wasn't enough clearance between the battery holder and the circuit board. In order to get the battery into the case, had to remove the holder, turn it around backwards, install the battery then push the assembly into the case with some insulating tape between the circuit board and battery holder. Whoever was assembling this probably realized that things weren't right and decided they would try to fix it with foam tape.
The punch out for the meter assembly isn't parallel to the edge of the bent sheet metal chassis.
The small punched-out metal key included to open the ferrite core on the top of the meter had razor sharp edges, which had to be filed down before using it.
To top it off, the "quality control' sticker, containing the QC inspector's initial, was falling off!
Functionally, the unit seems to work as it should. Should be noted in the instructions that for the three highest amperage ranges, the meter is powered by the induced RF current, hence will work even if the 'on' button isn't pressed.
If I had bought this at a ham fest, and had to fix these things, would have been happy, would have thought it was well worth it. But I bought this from a reputable online retailer, at a price consistent with a finished product, not a 'kit' that has to be finished by the user to get it to fit together properly. This is the part which is most upsetting.
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| WA1FEF |
Rating: |
2018-11-29 | |
| Ok,. But had to mod it |
Time Owned: 3 to 6 months. |
I had trouble with the power switch because:
1. The MFJ854 would only stay on for 15 sec by design. I was using on FT8 MODE which stays on for 15 seconds at a time. Had to keep hitting the power switch
2. During the end of the "on-time" the MFJ would peg the needle.
3. The power switch seemed poor quality and was intermittent.
I performed a mod to install a toggle switch in a 3/16" hole between the existing power switch and the range switch. I wired it across the existing switch contacts SW1-B. You can download the schematic from the MFJ website. Now I have no more intermittent switch and the unit stays on until I turn it off. Much better. |
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| K7TV |
Rating: |
2018-03-18 | |
| Needed fixing, but does the job |
Time Owned: 0 to 3 months. |
Bought this from HRO, since others didn't have it in stock.For many years I have been using a less expensive, similar unit, the MFJ-206. That unit has been very helpful in detecting RF current on the outside of coax feedlines (proving need for more common mode chokes; one CMS located at the antenna feedpoint is usually *not* enough), and trimming elevated radials for equal current (very critical if you can't run them perfectly symmetrically). The MFJ-206 does not give you an actual current reading, just relative values; the worst part is you can't get consistent readings, as small changes in how you hold the meter will have a huge effect on every reading. The MFJ-206 gets the job done only in a very approximate way. The MFJ-854 promised to provide actual current readings in a repeatable fashion. While the MFJ-206 just picks up some of the magnetic field depending on how close (and at what angle) you hold it, the MFJ-854 clamps a transformer core around the conductor being to be tested, similar to a clamp-type AC amp meter. I decided to pay the much higher price for being able to measure rather than just sense semi-quantitatively. Here is what I found.
* Opening the case to install a 9V battery, I noticed that the two screws were not grabbing securely in the chassis holes, which had almost no threads. The screws don't fall out, but it is close. I can probably find some bigger screws that will grab properly...
*The battery is to be held in a spring clip, but MFJ had installed a "cushion" of materials that prevented the battery from going all the way into the clip. I removed the "cushion".
* With the "cushion" removed, the battery fit well in the clip, with the "jaws" of the clip closing properly around the battery. However, with the battery in the clip, the little "ears" at the ends of the clip jawa were far enough apart that they prevented the clip with battery from passing into the chassis, and the unit could not be reassembled.I solved this by grinding down the "ears" using a bench grinder, while retaining enough metal that the clip would still hold the battery securely.
* The clamp that serves as current pickup seems to be a standard removable split ferrite bead with plastic locking housing of the type used for stopping RF currents on cables. I assume that it is not specified to block RF currents at HF frequencies, so as not affect the currents to be measured. It turned out to be annoyingly difficult to open the plastic shell around the ferrite. Instructions tell you to squeeze the plastic to unhook the catches. My fingers are not large, but it was still hard to reach the proper pressure points. With aching fingers I still found that the plastic clamshell would not pop open. I had to either use the other hand to pull it open, or use a tool to pry at the gap, all while squeezing way beyond comfort level.
* While the MFJ-206 requires tuning to frequency (as it captures only a tiny fraction of the field), the MFJ-854 needs no tuning, just setting to the proper sensitivity range.
* Last time I used the MFJ-206, I almost killed the battery by forgetting to shut the unit off. The MFJ-854 has an automatic shut-off timer that prevents such accidents. As someone already pointed out, the meter is pinned for a while during the shut-off sequence, but this appears to cause no damage.
* I went though the calibration procedure (50 W into 50 ohms should produce 1A full scale reading on the 1A range). Testing on 80m (to reduce the influence of reactance from short separate wires for signal and ground; you cannot measure current inside the coax!), using a Bird 43 and a Bird dummy load, I found that full scale reading required only 40W. I typically don't need exact currents, just repeatable readings and the ability to see small changes, so I didn't bother to adjust the meter, which should be easy to do if ever needed.
* Looking at the clamp I initially got the impression that the opening would not be big enough for RG-8 size coax. However, it turned out that RG-8 just fits, and without having to squeeze much to close the clamp. In any case, don't expect to fit 0.5 inch cable.
* Overall I find the MFJ-854 gets the job done for me, but unless I can find a way to open the clamp easily (maybe it loosens up with time?), I may keep the MFJ-206 as much more convenient when only rough current comparisons are needed.
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| KU3X |
Rating: |
2018-02-23 | |
| Great for trouble shooting common mode |
Time Owned: more than 12 months. |
I've owned this meter for about 4 years. I gave it a 4 because I had to calibrate it. It was way off from the factory. Super easy to calibrate, instructions are included in the manual. It's just a turn of a pot.
I have found so many issues of common mode with this tool. A friend of mine had a problem. Went to his house and looked in his back yard. Since the coax cables were so close to the RF field, even though baluns were used,I found it questionable when it came to common mode in the antenna area. Sure enough, I was right. All of the coax cables showed RF of the outside of the shield. Without this meter we would have never known for sure.
I am not saying this is a lab quality instrument, but it is far from junk. I am glad I have it and have found so many uses for it. It's not that I have issues, but this tool can confirm whether you have common mode or not. Remember, just because issues are not showing up in the shack, that does not mean that there is no RF on cables or coax in the shack.
If my unit gets damaged, I'd purchase another in a hear beat.
Barry |
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| G3XOU |
Rating: |
2017-07-03 | |
| More bad quality control |
Time Owned: 0 to 3 months. |
I found another problem with the MFJ-854. I was doing some current measurements on a doublet fed with 450 ohm ladder line and I was measuring 0.2A on the 1A range so decided to change to the 300mA range - then the meter hard end stopped!
Having checked the calibration on the 1A range which was correct I found that R10, the series resistor on the 300mA range was the wrong value.
It should be 15k according to the circuit diagram but they've fitted a 2k2 which can't be correct since the 1A range series resistor is 56k so dividing that by 3.333 works out at 16.8K which not being a precision instrument 15k would be the nearest preferred value. The 2k2 gives a full scale deflection of 40mA!
Anyway it is easy to change it as it is close to the outer edge of the PCB. This really is incredibly bad QA by MFJ. |
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| AB6G |
Rating: |
2017-01-19 | |
| Quality? Not! |
Time Owned: 0 to 3 months. |
I just received mine yesterday.
The battery fits into one half of the case shell.
The circuit board is in the other half of the case
shell. Once you insert the battery, on my unit,
you can not close the case because the battery and
holder will not fit between the sheet metal
and the circuit board.
Next, it is IMPOSSIBLE to open the cable clamp on my unit. I finally used pliers and a screw driver the pry it open. It claims to fit over coax up to 1/2. It will not. You run out of space before hitting .41 inch, so it is a no-go for RG-214 cable.
So, right out of the box, you can not use mine without mechanical engineering re-design. |
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| IK4YNG |
Rating: |
2015-01-23 | |
| BAD quality control |
Time Owned: 0 to 3 months. |
I have just received my MFJ-854, purchased new in the original box.
Upon arrival, it was not working.
A little investigation was showing the Sensitivity potentiometer badly miswired: the two leads were soldered at the extremities, and the cursor lead was disconnected.
Repaired, and still not working...
Then i found that one of the potentiometer's lead was NOT soldered on the PCB where it was marked POT1, but in another hole nearby, a grounding place.
Now, it seems to be working....
What a kind of POOR quality control!
IK4YNG Paolo
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