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Reviews Categories | Receivers: General Coverage | MFJ-8100 Help

Reviews Summary for MFJ-8100
MFJ-8100 Reviews: 20 Average rating: 3.4/5 MSRP: $89.00
Description: Genearal Coverage SW reciever
Product is in production.
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W3FIS Rating: 5/5 May 1, 2008 07:59 Send this review to a friend
Lots of fun  Time owned: 0 to 3 months
I first ran a parts inventory. All of them were there, though the list did not call out the IC socket for the audio amplifier. The regeneration and audio pots were not marked for values, so I need to break out the ohm meter to check them. The inductors for the tuning system are just like in the Ten-tec 1253, except for the single toroid to be wound by me.

There is lots of space on back panel for a UHF connector, battery jack, and toggle for the power. I want to be able to use an external power supply, and feed the receiver with a shielded coax, if I desire. I have a lot of EMI in the shack, so my antenna feed is with coax.

I will need to decide about the RF gain control, as it may be a little tight for a 10K pot I got at Radio Shack without drilling another hole. A careful reading of the instruction manual suggests that I won't have to adjust it often. This is the case on my Ten-tec 1253, where I only have to cut the RF gain back when I have one of those megawatt SW broadcast stations in the evening.

I can decided when I get the board populated and fit it to the case, and see what sort of space I have. At that point, I'll drill the hole for the power jack and power toggle (would have used "steering" diodes, but no good place to hang them). I couldn't find one of the power jacks with the built in transfer switch, or would have used that. I can just use my 5/8" Greenlee punch to punch out a hole for the UHF connector. I will leave their binding post in place, so I can easily switch from coax feed to wire, as I wish.

General small parts insertion and soldering went well. A 30 watt iron is clearly necessary to get enough heat. This board doesn't use the plated through holes that I am used to, so the soldering technique is a trifle different. As usual, examine each soldered joint as you make it, and then clip the excess wire off. Some of the pads are pretty close, and I had to fix one solder "bridge." The discussion on mounting the LED pilot light is simply wrong. You need it off the board about 1/4", and then bend 90 degrees to fit the hole in the front panel.

Larger parts need a little coaxing, etc., to get them in place, especially the main tuning capacitor. The single toroid is easy to do, especially as hookup wire is used to wind it. Mechanical assembly issues next, and I need to decide about the RF gain control. I think I'll go with the standard setup for the time being, so since I deferred soldering it in, I'll do that now.

Time to lay out and drill the holes for the power jack, power switch, and UHF chassis connector. I'm going to use one of the single nut attachment types, which has a locking washer under it. Neater in appearance, and no holes to get lined up.

Attaching the dial pointer is a PITA. Very tight fit. Reamed it open a tad with an Exacto knife, then secured it with a drop of contact cement. I also used some hot glue to secure the toroid to give it more mechanical stability. I also used more zip ties to secure the battery cable, etc. I still need to calibrate the receiver, but I'll do that some evening when I can hear WWV.

The tuning is quite smooth. The vernier tuning is just right for tuning in a regenerative receiver. Regeneration goes in and out smoothly. The usual stuff of tweaking up the regeneration point on the top band.

Right now, I'm feeding the audio through a amplifier/speaker, but headphones are quite satisfactory. I have not tried an external power supply yet, though of course, I do have the jack and switch in place. The current antenna is a 1/4 wave end fed for 40 meters that I use for my QRP transceiver.
HFHAM2 Rating: 4/5 Feb 27, 2007 01:13 Send this review to a friend
Works well !  Time owned: 6 to 12 months
This is a 3 transistor (FET) radio with an audio amp IC.

Doesn't sound like much at all does it but boy will it surprise you if you give it a decent length of antenna wire strung outside.

AM Shortwave Broadcasts, SSB, CW, it can resolve all of these and with good clarity too.

Yes, tuning and Regen require a safe-cracker's steady hand (could use a fine tune control) but that's all part of the fun!

Good construction/operation manual, solid case, unbelievable performance for the parts count, what's not to like?
CAPNROB97 Rating: 4/5 Feb 26, 2007 19:03 Send this review to a friend
Very sensitive with a slinky antenna  Time owned: 0 to 3 months
I bought the wired version from MFJ and it arrived today, along with a slinky antenna I bought off eBay that I am using with it.

I am currently picking up Trenton (Ontario) Military Aviation weather conditions (never heard this station before from FL, can't really tell what freq. it is, seems to be around 6.80 - 7.0 from the dial settings).

I am very happy with this rig so far. Utilities are fun to listen to, and this one pulls them in if you have the patience to 'work' the tuning on it.
AD5YU Rating: 2/5 Nov 27, 2006 11:30 Send this review to a friend
A little dissapointing  Time owned: 0 to 3 months
I bought this kit for my nephew (age 11) as an intro to Amateur Radio. We built it together over Thanksgiving. My problem isn't with the performance of the receiver, in fact it was a little better than I was expecting from such a simple design, however I was dissapointed with the kit & manual.
There were numerous errors/subsitutions that were confusing to my nephew, and the quality of the PCB was barely acceptable. I have built and tested many other kits including an Elecraft K1 and K2, and put together my own projects from scratch with PCBs I desgned and had made in Eastern Europe, so I have some experience with this. It is well within the cost structre of this kit to provide a decent PCB and an errata sheet to cover changes from the manual and instructions. I didn't feel like we got value for money, but the kit did eventually go together and work as expected.
KA8DLL Rating: 3/5 Oct 24, 2006 10:27 Send this review to a friend
fun radio needs a amplified ant . tuner for good ssb perform  Time owned: more than 12 months
This is a fun radio. With a amplified ant tuner for a little better front end selectivity and sensitivity. Don't worry about calibration,can't read the dial from any distance anyhow. For casual listening this is a nice radio. With some work this is a capable perfomer
KC2QCZ Rating: 4/5 Sep 28, 2006 18:52 Send this review to a friend
Remember what it is!  Time owned: 0 to 3 months
This radio is crud.
But yet I love this radio. Why? It's the first radio kit I every built, the first time I ever soldered, and it worked! The MFJ-8100 is very easy to put together for someone who has some theoretical knowledge of electronics, but no practial experience. The manual is comprehensive and very well written, but some of the components were of slightly different types than the book. Many of the capacitors were of different tolerance than the ones spec'd out in the parts list. For example, the manual says that there were 5 0.1uF capacitors labeled 104Z, but they included 4 0.1uF with 104M and 1 with 104Z. If one didn't understand the markings, one might be confused. Mounting the board was a pain, until I noticed a little plastic mold nubby on the case of the bandswitch. I nipped it off and then everything went together nicely.
Receive performance with a random wire about 20 feet long, is, frankly, abysmal. I did pick up a number of SSB signals, but there's no real way to tell what frequency, as calibrating the dial (actually described in the manual!) was beyond my patience/skill. My $20 pocket shortwave radio works better than this over a larger range with much higher sensitivity. So why did I give it a 4? Because one should keep in mind what this is. This is an introductory kit for people with little/no experience to build, and there's a great joy in finishing the radio and then turning it on for the first time, and actually hearing a signal, badly distorted and noisy, but still a signal! From a device built with your own hands! And that's worth the price of admission.
I should point out that the case provided is very nice, and once the you close up the case, it looks very professional and commercial.
K3MD Rating: 5/5 Dec 25, 2005 14:56 Send this review to a friend
Fun  Time owned: 0 to 3 months
I bought this unit pre-assembled. It out-performs my other two regenerative receivers by a wide margin. It is a little tricky to tune in CW, as expected. It would make a good QRP receiver for 80 or 40 meters, as long as the spotting signal were attenuated. Nicely written manual. It does fine on the SWL bands, no problem. There is a little bleed-through from AM brodcast, they have filters for this, not unexpected. Regeneration is stable and smooth. An RF gain control (on the back panel) is a nice touch.
W7AAR Rating: 1/5 Apr 18, 2005 11:25 Send this review to a friend
Don't waste the $  Time owned: 0 to 3 months
Built this as a warm up for my KX1 and to give my grandson the experience as well. Rather simple kit but several parts(pots) were mislabled/misnumbered/not numbered. Dial pointer is impossible to put on without breaking it. Tuning accuracy/dial is one notch above a crystal set. Did work somewhat after I hooked it to my Windom but overall seemed very marginal. I have an MFJ keyer that works just fine but this will be my last MFJ purchase.
KO4MH Rating: 4/5 Feb 13, 2004 17:50 Send this review to a friend
Works well for me  Time owned: more than 12 months
I built this receiver kit several years ago and it works well for me. Frankly it is amazing what sensitivity these regens can give - although you must adjust a little as you change frequency. I use a 20 foot wire for my antenna. Works well demodulating CW and SSB, although, as you should expect, the selectivity is nowhere near a good superhet.
As another reviewer pointed out, stability is a little problem (mine shifts frequency as you move the headphone cord around, but its not too bad). In summary, I like it. I use it periodically and enjoy playing with this old, but neat kind of receiver architecture.
N8BEG Rating: 0/5 Dec 12, 2003 20:14 Send this review to a friend
terrible performance....  Time owned: 0 to 3 months
To qualify this viewpoint, I have built many recievers/transmitters in my life. Many, I have designed. And, I have built regens before. So I knew what to expect. This radio is a regenerative reciever, but, if you read the MFJ literature on this radio, they talk about it being "an improved design" over the popular regen designs, etc...etc........they sell it beyond it's capabilty. I wanted a small radio; battery powered that would recieve CW/AM/SSB that I could take to Hunting camp; on the get the idea. I was very dissapointed. It isextremely unstable. You can't tune or find anything...the regen sensivity changed radically with every turn of the dial ( this is normal with the REGEN approach but, there are ways to minimize this by limiting bandspread, etc) . The sensitivity was irregular. BOTTOM LINE: .....this thing sucks. This radio is not worth $20........
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