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Reviews Categories | Filters, RF: bandpass, lowpass, highpass, RFI/EMI, etc.. | MFJ-704 Low Pass Filter Help


Reviews Summary for MFJ-704 Low Pass Filter
MFJ-704 Low Pass Filter Reviews: 6 Average rating: 3.5/5 MSRP: $49.95
Description: This is a nine pole Chebyshev filter with an insertion loss of not more than .5db from 1.8 to 30 Mhz. This filter is designed to accept up to 1.5 KW of power at a frequency of 1.8 to 30 MHz. The purpose of the low pass filter is to reduce possible interference from your transmitter to television or other services above 30 mhz.
Product is in production.
More info: http://www.mfjenterprises.com/products.php?prodid=MFJ-704
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You can write your own review of the MFJ-704 Low Pass Filter.

G4AWJ Rating: 5/5 Sep 29, 2012 06:50 Send this review to a friend
DOES WHAT IT SAYS ON THE TIN  Time owned: 0 to 3 months
Since my local Analogue TV Station whent digital, so with linear running at 400 watts I was wiping out my main TV pictures, found that the ARRL had in the past spoke well of the MFJ-704 filter, found one on e-bay at a good price, new from ATHENS, Greece, open it up and found soldering and construction very good, now inline with my Linear output to ATU and now have freedom
again on the ham bands (always keep the station manager happy and so enjoy uninterrupted DX'ing)
well done MFJ
 
2E1MPC Rating: 1/5 Feb 3, 2009 13:41 Send this review to a friend
poor quality  Time owned: months
Same problem from new, no continuity input to out , dry joint , crap ,,,,,,,,,,,,,,,Didnt work with rfi any way
 
VR2AJ Rating: 2/5 Nov 18, 2004 02:28 Send this review to a friend
Products without QC is normal  Time owned: 0 to 3 months
One more review can be added on the list of problem with soldering. Last night, I received the filter and tested it with complete connection, well no signal through it at all, open it and saw what happen inside, I found that they have miss-connected the input terminal caused by soldering, so I soldered it by myself. And then I performed a test with my spectrum analyzer to see how about the cut-off frequency. The cut-off frequency was above 33mhz, it seems to be fine, but a free-function is putting on, a bug as non-filtering signals from 272mhz to 280mhz.-8 DB was been displayed, that mean it can pass the said frequencies actually. I'm here still having TVI on 10m., and looking for best way to solve it, anyway I will never to buy this brand's product. 73,
 
2F9MS Rating: 4/5 Apr 1, 2004 20:22 Send this review to a friend
TERRIBLE QUALITY CONTROL  Time owned: 0 to 3 months
I PURCHASED MY MFJ 704 BY MAIL ORDER FROM WATERS AND STANTON AFTER READING THE ABOVE REVIEWS I THOUGHT I WOULD TRY MY LUCK.ALL WAS OK UNTIL I WENT TO CONNECT THE PL 259 TO THE INPUT. I FOUND THAT THE THREADS HAD NOT BEEN CORRECTLY CUT,SO I DID THE JOB FOR MFJ AND RE CUT THEM.THEN I FOUND THAT I HAD HIGH SWR WHEN ALL LEADS WERE CONNECTED SO I REMOVED THE TOP AND MY GUARANTEE TO FIND A DRY JOINT,OUT WITH THE SOLDERING IRON THEN BACK ON WITH TO TOP 30 SEC JOB.I AM HAPPY WITH MY WORK AND I NO LONGER HAVE RFI PROBLEMS. MFJ 50+SOME DIY BUT NO RFI.TERRIBLE QUALITY CONTROL FROM MFJ.
 
G0RGU Rating: 5/5 Nov 18, 2002 16:51 Send this review to a friend
Checks out ok  Time owned: more than 12 months
I bought this low pass filter about 9 years ago but the spec seems to have stayed the same. I didn't have TVI problems but just bought it as a precaution. As another review says there isn't much to it - a strip of pcb type material to form the capacitors and five chunky air spaced coils across them. However the casing is solid enough and it's a nice looking shack accessory.
I've done some tests with the filter and on the HF bands the insertion loss is within 0.5db as stated - very little signal loss on a fixed signal source when inserted ( barely a needles width worth ). You'd never notice the difference.
The cut off frequency is stated as around 40 Mhz but I could only test it on 145 Mhz with a very strong local station. From being s9 + 30db gain down the signal was attenuated to s1 gain full up - a very respectable attenuation at VHF - I was convinced it was working well.
If you think your station is radiating harmonics above 40 Mhz then I believe this filter is a winner. I just have it in line just in case.
Yes, some MFJ products seem to have terrible quality control, others are great - read the reviews and test any gear you buy. I have the MFJ 1782 magnetic loop and the MFJ 948 antenna tuner - both good products.
 
ADAM12 Rating: 4/5 Nov 18, 2002 00:42 Send this review to a friend
Works as good as any  Time owned: more than 12 months
I've been using one of these for a few years now with no problems. Low pass filters have been described as being like a "lucky rabbit's foot". They work sometimes for some people in some situations but there's no magic involved.

Yes, there's not much to look at inside these (just a few air-spaced coils) but mechanical construction on mine was fine and as far as MFJ goes, yes, sometimes you have to re-solder the odd joint or tighten the odd screw, but for what you're paying for MFJ products, can you really complain ?

ARRL did a survey on low pass filters and this MFJ one came out amongst the top for RFI/TVI suppression.
 


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