The AM Forum

Does anyone have any experience with this inexpensive (compared to a MFJ 919) balun?
http://www.ebay.com/itm/BALUN-4-1-JETSTREAM-HIGH-QUALITY-LOW-PRICE-AND-SHIPPING-/150636896210?pt=LH_DefaultDomain_0&hash=item2312a89fd2

for similar money you could get Unidilla unit.
Just stream is made off shore, everything that I have heard about Jetstream stuff they some folks have not been happy with the stuff.
But that is only the grape vine..

How do they expect you to make antenna wire connections to this thing:

(http://www.mfjenterprises.com/pictures/MFJ-919.jpg)

Do yourself a favor,  skip the balun and just connect your coax directly to the antenna.

Just my 3 cents (use to be 2 cents but with inflation it has gone up)

Fred

If you are concerned about current on the shield then get some of the beads for your coax from Palomar.

Current on the shield is a topic I have never seen discussed here nor operation with open wire line if you are off resonance from your antenna.

Problem is, I bought a couple of the MFJ 1777 doublet antennas, they "say" they should have a 4:1.  Your opinions? Please.

Since that is the case, I would stongly consider building a K1JJ tuner for balanced line.  Baluns can pose problems in the long run.

I don't care for MFJ i would buy a radioworkz or unadilla or just a rf choke I don't know what you got going on!

Well, whats going on is, MFJ says to use a 4 to 1 balun and an antenna tuner to get the best results with their doublet. So I am trying to decide which baluns to buy.

Obviously, a customer reviews of balun manufacturers  probably would be worthwhile: http://www.eham.net/reviews/products/1

Some of the "best" and "robust" baluns on the market today come from DX Engineering. There's also numerous articles on the web for making your own 4 to 1 baluns.

MFJ isn't bad for some things--I use their swr analyzer and phase shifting nulling box to get rid (or try to get rid) of local RFI but I'd stay away from anything the make that has to do with antennas, feedlines and tuners.  I have seen their tuners and I'm not impressed, but you are talking about baluns.  AM is usually a balun killer.  You can get a balun that will take the AM duty (http://www.balundesigns.com) but you have to be able to support the weight at the feedpoint, and limit the use of the dipole to one band where it has to deal with a ~70 ohm Z.   Forget about using it on multiple bands and tuning the line at the shack. 
IMO you are far better off using ladder line and a balanced tuner, but not any balanced tuner--a link coupled tuner that has the balanced line floating above ground is a must.  I.e. the coil has no center tap that is grounded. 

Balanced feedline tuners have gotten attention in the past few years so the market has several varieties out there.  If you buy one (instead of building one) you have to be careful.  Beware of names such as MFJ's "Balanced Feedline Tuner."  That is clever wordplay for it is not a balanced tuner, it is a tuner that tunes balanced line (in reality a  non-symmetrical T network).  The Palstar tuner (way over priced for what you get) is a genuine balanced tuner but it is not a link coupled tuner--it does not isolate the balanced line and prevent common mode RF from getting to the low Z coax feed to the shack.  (all this is assuming your radio gear is designed to deal with an unbalanced normalized 50 ohm line).   If you don't build one, your best bet is getting a Johnson KW Matchbox.

If you have room for multiple dipoles using coax is still an option, just don't use skinny lossy line. 

A genuine balanced tuner is either link coupled or has the balun between the transmitter and tuner, and uses a symmetrical tuned circuit, either with two separate identical tuning capacitors or a single split-stator one.

Many of the commercially manufactured "balanced" tuners on the market to-day are totally bogus.  They use an unbalanced L- or T- network to feed the open wire line through a balun. That might work OK when the OWL is working as a flat, untuned feed line, but is a bad idea for working into a tuned feed line, if the load has any substantial reactive component, or is a high impedance (something that would normally require parallel tuning with a balanced link-coupled tuner).  One of those tuners MIGHT work OK if the OWL resonant feeder is being fed right at a current loop where the impedance is low with little or no reactive component. But it probably wouldn't be satisfactory on any other band with that antenna.

Transformer-type baluns like the ones used in those tuners are  designed to handle a purely resistive load at a narrow impedance range.  Force-feeding a reactive load of random impedance through a balun may result in excessive losses and cause the ferrous core to heat up (sometimes to the point of self-destruction), and even worse, may drive the core to saturation, causing it to become non-linear, resulting in spurious radiation products, exactly like what happens when antenna-to-feedline connections become corroded or certain dissimilar metals come into contact.

Don, (and others),
                         this is another question that has been discussed
ad nauseum here. I agree with you on the balanced tuner/tuned feedline scenario. But, however, there are times when you just cannot do it that way. But, you still want to use balanced line for as much of the feeders as possible.
I have that very scenario at my QTH. Bad load/short antenna,shouldn't work at all.

But wait! ! ! ! ! It does work very well if done properly. It is a bit of a challenge to get it to work properly, but it can be done. My signal is living proof!

First off you have to supersize everything to handle the high currents and minimize the I2R losses. (overkill is your best friend here) I am using a "T" type tuna. a very short run of coass, and balanced feeders to the ant. The "T" type tuna gives you some extra "range" in the amount of mismatch that it will handle.
The balun has to be built to withstand blasts, and the feedline has to be beefy.

It was a Trial and Error process to find out what would work, since everyone said it wouldn't. The tuna fills a box the size of an R-390a with 2 caps and a massive edgewound roller inductor. The balun was the result of a discussion one night with Chris (W2JBL ex KD2XA) when he told me "you cant build a balun that will work / survive, period, undoable". Just to prove him wrong, I started experimenting and finally came up with one that was indestructable.

I rolled it all together and it has been working with the 4X1 at full strap for 10 years now. Here is the antenner and balun that I am using. (Been using it for over 10 years now!)

It just takes some futzing around to come up with something that works. Experimenting is half the fun.

Very carefully.................... ;D  ;D

Make a couple of them for about 10 bucks each. A 4:1 air core balun to cover 2.5 to 15 MHz is described in the 1975 edition of the William Orr edited Radio Handbook.

The air core type will not cover the whole 1.5 - 30 MHz range like a ferrite core balun will, but it will not saturate and is efficient and you can make it out of almost anything including # 12 insulated house wire.

It consists of 7 bifilar turns of #12 Enameled or Formvar wire on a 2 3/8" diameter PVC pipe. This gets you 80, 40 and 20M.

10 bifilar turns gets you 160, 80 and 40M.   

10 bifilar turns on a smaller diameter tube like 1" or 1 1/16" will get you above 30 MHz and should do 20M - 10M

This guy even used stranded wire and it worked OK. http://rogertango.com/articleread.aspx?idnumber=34232411

Then buy the MFJ balun. No one who has responded has the MFJ doublet or has ever used the balun in question, so I'm not sure how they would be able to give you good info. If the requirement is no more complex than needing a wideband 4:1 balun, there are many others on the market. You can evaluate the worthiness of these based on your power handling requirements and availability of funds.  ;)

The MFJ 1777 is simply a 102 ft dipole with window line coming down all the way instead of a transition to coax ala the G5RV.

If your tuner has a "Balanced Line" connection, then it already contaings  your 4:1 balun inside it.  (or it is a TRUE Balanced Line tuner).

Before worrying about a balun, decide on your tuner.  Maybe a Johnson Matchbox will do a great job for you, it is a balanced tuner w/o the need of a balun.  (I doubt you're going to run 160 with 102 ft unless you configure it as a T vertical against ground).

Remember, MFJ says you need a balun because most hams today are pocketbook hams that buy ready made gear and would not actually buy a real balanced tuner.

Frank,
when I use a transformer on the input of the fugly I use the same thing you have but only 6 cores. fc

The balun in my "3KW" MFJ T tuner is useless.   I have a window line fed doublet far from my house, yet on 40M to 160M I was picking up a lot of house noise.   I did some measurements and found there was no balance at all on 80M.    I did some research on the internet.   There was a web site that compared losses of several commercial baluns.    From that info, I purchased one from DX Engineering that was made for use in high swr.   The noise disappeared and it does not get warm when running 175W AM or high power SSB on 80M to 10M.   My antenna is short for 160M, but I can't run a lot of power on that band.   I think it would probably get hot on that band if I had the power.

Many of the "baluns" in commercially made tuners are about as worthless as bumps on a log! (as well as the tuners)

When I started playing around with high powered AM it opened up a whole new can of worms. Most of the better "high end" tunas would be fine with a typical 100w table top boatanchor (Dixie 100, Viking 2, Apache, etc) But when you added high power to the equation all hell would break loose! !

I melted tunas, had baluns either catch on fire or blow apart, and all kinds of fun stuff! That was my real incentive to come up with stuff that could handle the power into a bad load. I have used the short antenna that I posted earlier on 160 with fairly good results for it's size.

I am stuck with a short antenna due to my small lot size, so the challenge was coming up with something that would work. After coming up with an antenna design that fit the yard (out of an OLD west coast handbook) The new challenge became making everything live with high power after I built the 4X1 rig. It was an interesting challenge making it live at full strap.

After melting tunas, blowing baluns to bits and starting fires, I found that overkill was my best friend here. (I am dealing with extremely high feedline currents here, and have even burned PL-259s off of the short coass between the tuna and the balun. (on 160) I built everything to the point where NOTHING even gets warm after extended "old-buzzard" transmissions. No heat means no loss! !  Short, Sweet, and Simple.

Build the tuna to handle at least  double the maximum power you ever plan to run, and the balun to handle 5x the maximum power you plan to run and forget about it and live happily ever after!

As far as the balun goes, I built all shapes and sizes of them and swept them all. I found that most of the 1:1s got wierd when you strayed away from their charactoristic design impedance, adding a large reactive component of their own. Most of the 4:1s held a good 4:1 impedance ratio no matter which way you changed the inpoot impedance, and added negligable reactive component of their own. If you are using a ferrite core transformer, besure to use enough ferrite that it doesn't saturate or  get warm under load. Weight is your friend here!!


Just my $.02 worth..........

My situation is such that I bought two of the MFJ 1777 antennas, one is oriented North-South, the other is East-West. I can switch the coax a lot easier than trying to deal with ladder lne coming in the room.  I plan to only use 75 and 40 meters, and less than 1KW at any time. I also have the BIG Heathkit antenna tuner.

I've managed in my AM rebirth to avoid baluns.  160 m. antenna is unbalanced inverted L.  Balanced antennas 80 and up get the KW Matchbox.  Everything is okay for now with 300 w. 

https://www.amidoncorp.com/items/89 

70 bucks.  Put it behind that Heathkit tuner and you'll be all set even if you decide to go QRO.

I have two of the Balun Designs Inc 1:1 running at 250-350 W AM plate modulated on 40m and 80m.

No smoke yet.

I'm not running a flamethrower here (yet), but I had a problem with RF coming back into the shack on the line to an antenna. It was so bad that it was locking my FT-897D in transmit mode when I unkeyed. Talked to Bob of Balun Designs at a 'fest and he recommended his #1113u isolation balun to solve the problem. It worked fine and I've had great results ever since. Looking inside the unit, I have no doubt that it would hold the advertised 3 KW power limit. Nice guy and great product. I'm happy and recommend his products without reservation.

ldb
K5WLF

if you got rf in the shack check your grounds short  rf choke works or a unadilla makes a few check them out look on scope you will see the rf on waveform turn down mic see goes away if that's case need go deeper not antenna