MFJ-17754 40/20 Meter Dual-Band Dipole

[Alan Georges]

Last year I reviewed this thing's big brother, a similarly constructed 80/40m dipole (http://thesurvivalpodcast.com/forum/index.php?topic=44578.0).  It's still working great, even after a year out in the weather.  So I picked up the smaller 40/20m for go-gear, and it works great too.

Beyond saying "same thing, just 2x smaller," here are a few more particulars:

- I rigged it as a 90deg inverted V, from a 20' PVC mast.  Tuned up pretty easily.

 - It covers both the 20 & 40m bands completely, though admittedly the SWR was pushing 3 at the edges of 40m.  An internal tuner like some HF rigs come with can handle it fine.  So it will let you do CW, PSK, etc. on its longer band and still let you talk on that band too, without going outside to lengthen or shorten any wires.  This is in contrast to the 80/40, which will do all of 40m, but can only handle about the bandwidth of the phone portion on 80m– or the code portion if you choose to lengthen things out, take your pick.  Anyway, this smaller one will handle all of 20 & 40m bands while keeping the SWR < 3.

- Works great!  Talked to Carl last Sunday on 40m with the bigger 80/40 and on this smaller 40/20, and got a better signal report (maybe an S-unit or so) on the smaller antenna.  Of course, band conditions were bad-to-variable at the time and it was only one QSO, so this wasn't exactly a thorough test.  But I'd say, compared to a full-sized 40 similarly deployed, this trap dipole doesn't compromise the signal in any significant way.

- Maybe my usual 20m double bazooka is a tad quieter, it's hard to tell without having the two up at the same time.  Anyway, this thing works about as well on 20m, and I made a few phone and PSK contacts on it in these tests.

- Its yard footprint is much, much smaller than that of the 80/40.  As an inverted V from a 20' pole, it's only about 40' long.  Lots of yards can manage that.  (Your HOA may be another matter...)

- The copperweld wire is thinner and easier to handle than on the 80/40m.  It doesn't tangle so much, and if it does, it's much easier to sort out.

- With those last two items, this antenna much more go-bagable than its 80/40 big brother.  The whole thing spools up fairly neatly around a plastic coffee can, and my 2m slim Jim rolls up inside the same can.

Looking at the results from a poll on which HF ham bands people use (http://thesurvivalpodcast.com/forum/index.php?topic=50705.0), it's pretty clear that 40 & 20m are the two most popular ones.  It makes sense to focus on these for a go-kit, and the trap coils give this antenna 40m capability for not much more length than a 20m-only.  I won't say that it's the perfect HF antenna, or even my favorite HF antenna, but if I could only have one antenna this would probably be it.

Here's a link to the mfg's web site: http://www.mfjenterprises.com/Product.php?productid=MFJ-17754  The list price is about $60.

[Carl]

And I must add that Alan and I are only 200 or so miles apart and that represents NVIS ,a near vertical bounce of the signals to come back to earth that close. It in no way indicates a weakness of the antenna or installation of the antenna. NVIS makes HF HAM a viable medium range communications mode.

 The gear ,at my end,is a 20/40 meter inverted "V" with wires for each band tied to a 1 to 1 balun as a common feed point...with these two wires 25 feet at highest point,I work 40 and 80 meter NVIS,and all bands 80 through 6 meters with my radio's 3 to one internal taking up the slack from not having a set of wires stretched for each band.

My radio,powered by solar charged battery, runs at about 20 watts (though I could turn it up to 100 plus ,if needed) as power is really not so much a component of capability as are propagation and antenna...and LUCK.

My antenna is loosely modeled after a military command HF antenna the AS-2259 , below is a link to some modifications and original plans to set up your own,with a auto or manual tuner it covers all HF bands.These file are FREE,just as I found them,and if you claim ownership...I will gladly remove them on request. Hosted on my Google Drive for safe downloading.

https://drive.google.com/folderview?id=0B5ZIZLZV4AwIY3NoMkthTEVQRE0&usp=sharing

[Saint-TyR]

My antenna is loosely modeled after a military command HF antenna the AS-2259 , below is a link to some modifications and original plans to set up your own,with a auto or manual tuner it covers all HF bands.These file are FREE,just as I found them,and if you claim ownership...I will gladly remove them on request. Hosted on my Google Drive for safe downloading.

https://drive.google.com/folderview?id=0B5ZIZLZV4AwIY3NoMkthTEVQRE0&usp=sharing

Awesome! Thank you for sharing! I am just getting into the HF set-up and I am always looking for another antenna system that can be set up  and taken down quickly.

Stay Safe!

[Carl]

Awesome! Thank you for sharing! I am just getting into the HF set-up and I am always looking for another antenna system that can be set up  and taken down quickly.

Stay Safe!

With the files I hosted,many versions ,or variations,of the AS 2259 can be tried. all with the same 'basic' configuration and modifications for various additional bands etc. With an auto tuner (LDG is a favorite) at the antenna feed point  you have a very frequency agile,LOW LOSS ,due to tuner at antenna end of feed line, antenna system that uses a single support and ground anchors to support it...I have tossed a parachute over the antenna ,with me and vehicle under the shade/camo to take advantage of a system that takes minutes to errect and has so much potential for NVIS and long distance communications...PLUS is a usable shelter..the mind wobbles with possibilities.

  My home antenna is the slightly modified version with a proper 20 meter and 40 Meter wire (40 just 2 feet over true cut length) to provide full coverage of 80 thru 6 meter bands ..3.4 to 54 MHZ with the auto tuner! it is cut for 20 and 40 meters as they are my most used bands and I do gain just a little TX and RX improvement with wires cut for those bands. But the AS 2259 offers many possibles in a small package , my backpack version uses a 20 foot carbon fiber fish pole that weighs near nothing,collapses to 18 inches ,and the whole antenna(with auto tuner) weighs just a few pounds and fits in a day pack with the radio , battery (lithium ion) and 10 watt solar -folding panel. I know ,I am a little light on the solar, but these days I don't stray far from the vehicle as age,diabetes,and cancer ...have a way of slowing one down a bit.

[Canadian Prepper]

Thanks fellows!

That's lots of info to digest about both the MFJ and NVIS antennas. I'm hoping to augment my MFJ portable vertical with another reasonably portable setup. Just my luck the local ham outlet only carries the 40/80m version of the dipole discussed by Alan, which might be just small enough to fit in my yard. I might just have to ask them if they can order it for me.

I was looking at the MFJ 33' telescoping pole several weeks back, but decided that since it could only really be used for an end fed at my location that it wasn't really that much of an improvement over what I've got for over $200 once everything is ordered and shipped. OTOH, I could get a 20' crappie pole around here for about $20, and if there's an antenna setup that would work with it, that would be perfect. The provincial emergency net up here uses 40m, and an NVIS setup would be perfect for covering the region.

[Carl]

A good LOW dipole or inverted "V" is needed for NVIS, The vertical ,due to take-off angle is better suited to long distance use. Proper antenna selection and band selection are critical for targeting a receiver rather than just throwing your RF dart into the air to see where it will land. A good DX (distance) working antenna is a poor choice for intermediate distance use,where a good NVIS  antenna will also do reasonable at long distance. Like skipping stones across a lake,proper stone and angle make a lot of difference with the results.

[armymars]

Canadian Prepper,
  I used the Crappie poles for two years, once a week all year long to run my morning net for Mars. I had to use two of them to hold up my two dipoles. The dipoles were for 3.3 MHz and 5.4 MHz. The fishing poles were 17' long. After two years of all kinds of weather 11*F to 96*F they started to crack at the joints. Sometimes I would be in a net and a big wind would come up. They would telescope in and I would go from S9 to S3  that fast. Oops.
  The G5RV is popular in Mars for NVIS. We have found over and over again that they work best at 35 to 37 feet. The Inverted Vee has a bowling ball pattern on 80 and 40 meters at that height. You can't go to much higher in frequency and still get NVIS. My 60 meter NVIS antenna for Mars is only seven feet off the ground, but I'm 2 S units lower in signal strength. My noise is much lower to. 

[Alan Georges]

Thanks for posting all of this NVIS info Carl.  Yes, I looked long and hard at an AS-2259 last year, and that MFJ 80/04m seems close to being a civilian analog of it.  I really like operating NVIS on 80 & 40, because it's mostly regional contacts I want.  That, and the antennas and masts are simple and inexpensive, and easy to take down before a hurricane and set back up afterward.

Canadian Prepper,
  The G5RV is popular in Mars for NVIS. We have found over and over again that they work best at 35 to 37 feet. The Inverted Vee has a bowling ball pattern on 80 and 40 meters at that height. You can't go to much higher in frequency and still get NVIS. My 60 meter NVIS antenna for Mars is only seven feet off the ground, but I'm 2 S units lower in signal strength. My noise is much lower to.

A tenth to a quarter of a wavelength is the usual height.  Below a tenth and the signal takes a hit from ground attenuation; above a quarter and the waves don't beam upward as tightly.  None of this is seems too critical, and 35'-37' sounds like you've found a sweet spot for the bands you're working.

At 20', my center support on the 80/40 is a tad low for working 80m.  Next iteration I'll probably push it up to 30' and maybe pick up an S-unit or so of gain.  But for the moment I'm still pretty happy with it.

[Carl]

When antennas go higher,they pick up more noise. When dealing with NVIS,your signals are just a tiny percentage of power reflected back to earth. I always opt for LESS ,it noise and signal go down equally then your change does little as "S" unit is just a number. I have found that lowering the antenna removes way more noise than it does signal. I would do a true dipole (not inverted "V" I use now) at 8 to 9 FEET and benefit from low noise and good reflection.

Also a slightly longer wire on the ground as a reflector will better define 'ground' and improve receive strength PLUS help stabilize the transients that received signal often fades in and out.

For Katrina comms ,we used dipoles at roof top level and so many people offered to help us put our antenna up correctly (yes ,they were often HAMs too) that we had to hide in a neighborhood to get enough peace to pass our traffic. Also military trucks were a SNAG in the antenna as they were often too tall.

[Canadian Prepper]

A question for you fellows, as this seems like the group who could give me the advice I need.

the back yard I've got to use is about 17' (though I might be restricted to about 13-14') by approx. 30', perhaps a bit longer, and there's a balcony on the second floor from which I could probably hook up the center of an inverted V. The problem is that I'd have to not only keep the wires fairly low (perhaps a good thing) but that I'd probably have to tie both ends down at the far North end of the yard just 10-12 ' apart from each other (like a v shape from above). Perhaps I could alternately do something with two crappie poles at either end of the yard, but those would at best be only 30' apart. Thus even a half length 40m G5RV or the MFJ that's the subject of this thread could hardly fit into such a yard and even that's with the dubious setup.

I'll be adding some extra radials to my portable vertical today and am not giving up on it, but I'd like to try something different and even an NVIS setup would have practical application for me, but it's all about playing with such limited space. Perhaps once I set up my power system for more portable use in a park I'll be able to properly setup a 50-100' dipole, but in the meantime I'm trying to play around with other options. If those end up being fairly portable that would be a bonus, as the ability to deploy with my kit is a medium term goal.

[Alan Georges]

Folks, this is getting pretty far from a review of a 40/20m trap dipole antenna.  I'm grabbing the discussion of NVIS by the nose-ring and dragging it over to an existing NVIS thread.  But if there's any more questions or comments on the 40/20 antenna review, keep'em here.

Here's the link to that NVIS thread: http://thesurvivalpodcast.com/forum/index.php?topic=45413.msg580568#msg580568

[Alan Georges]

A question for you fellows, as this seems like the group who could give me the advice I need.

Hey CP, I'm going to post an answer over at the NVIS thread momentarily.

(Dangit, these threads are getting all crossed up.  It's what I get for watching the movie Primer while drinking Mississippi Fire Ant beers last night.)

[Carl]

A question for you fellows, as this seems like the group who could give me the advice I need.

the back yard I've got to use is about 17' (though I might be restricted to about 13-14') by approx. 30', perhaps a bit longer, and there's a balcony on the second floor from which I could probably hook up the center of an inverted V. The problem is that I'd have to not only keep the wires fairly low (perhaps a good thing) but that I'd probably have to tie both ends down at the far North end of the yard just 10-12 ' apart from each other (like a v shape from above). Perhaps I could alternately do something with two crappie poles at either end of the yard, but those would at best be only 30' apart. Thus even a half length 40m G5RV or the MFJ that's the subject of this thread could hardly fit into such a yard and even that's with the dubious setup.

I'll be adding some extra radials to my portable vertical today and am not giving up on it, but I'd like to try something different and even an NVIS setup would have practical application for me, but it's all about playing with such limited space. Perhaps once I set up my power system for more portable use in a park I'll be able to properly setup a 50-100' dipole, but in the meantime I'm trying to play around with other options. If those end up being fairly portable that would be a bonus, as the ability to deploy with my kit is a medium term goal.

My yard is 55 feet wide and has power lines 5 feet inside one side. A 20 meter wire fits side to side just fine without getting too near the power line feed of the house. My 40 meter wires are an inverted "V" and also "V" to the back of my yard so as to fit and yet not risk the power line contact.

  Antennas are drawn as strait lines because strait lines are easier to draw. take the antenna as wide as you can,but a 'bent' antenna is way better than a short antenna. My first inverted "V" went out to the side limits and then both legs came back to a center insulator...looking much like a coat hanger in profile. Make sure your antenna is long enough....but strait is just one of many options.

  YES,the radiation pattern may skew a bit...but odds are you will never notice it.

My two cents,and few have challenged me with being wrong...they discovered they were mistaken.

[Canadian Prepper]

When antennas go higher,they pick up more noise. When dealing with NVIS,your signals are just a tiny percentage of power reflected back to earth. I always opt for LESS ,it noise and signal go down equally then your change does little as "S" unit is just a number. I have found that lowering the antenna removes way more noise than it does signal. I would do a true dipole (not inverted "V" I use now) at 8 to 9 FEET and benefit from low noise and good reflection.

Also a slightly longer wire on the ground as a reflector will better define 'ground' and improve receive strength PLUS help stabilize the transients that received signal often fades in and out.

For Katrina comms ,we used dipoles at roof top level and so many people offered to help us put our antenna up correctly (yes ,they were often HAMs too) that we had to hide in a neighborhood to get enough peace to pass our traffic. Also military trucks were a SNAG in the antenna as they were often too tall.

Interestingly enough Carl, I just attached another 21 radials to my vertical today (it had 16 beforehand and only four originally) and was getting mediocre receive with the MFJ tripod extended about 6ft high. Admittedly most people I could hear were complaining about conditions mid-afternoon, but I decided to lower bipod down about three or four feet and found that it receives much better on 40 and 20m. The 14ft radials also sit much better on the ground than when the bipod's extended, which places about half of the length in the air.

I also decided to try out my 80m MFJ Ham Stick from my mini-dipole and discovered that it seems to tune in nicely at 3.755 (a monitored frequency for a provincial group) and 3.818LSB which is the wintertime AMRRON frequency. While the Ham Stick only tunes into a narrow frequency range it also seems to do better with the radials, that I suppose provides something closer to a vehicle than when it's just mounting it to the bipod on its own or with the four radials that came with my vertical antenna.

This isn't exactly the same thing as trying the MFJ dipole or the true NVIS route but it's still interesting to note how the combination of adding radials and lowering the vertical seem to make a big difference. Perhaps if I finally pick up an antenna analyzer I'll be able to figure out what's really going on. In any case I think I'll have to measure out the yard to figure out what can be done with the available space.

[armymars]

Canadian Prepper. Carl,73d I posted something on the other thread.

[Carl]

Interestingly enough Carl, I just attached another 21 radials to my vertical today (it had 16 beforehand and only four originally) and was getting mediocre receive with the MFJ tripod extended about 6ft high. Admittedly most people I could hear were complaining about conditions mid-afternoon, but I decided to lower bipod down about three or four feet and found that it receives much better on 40 and 20m. The 14ft radials also sit much better on the ground than when the bipod's extended, which places about half of the length in the air.

I also decided to try out my 80m MFJ Ham Stick from my mini-dipole and discovered that it seems to tune in nicely at 3.755 (a monitored frequency for a provincial group) and 3.818LSB which is the wintertime AMRRON frequency. While the Ham Stick only tunes into a narrow frequency range it also seems to do better with the radials, that I suppose provides something closer to a vehicle than when it's just mounting it to the bipod on its own or with the four radials that came with my vertical antenna.

This isn't exactly the same thing as trying the MFJ dipole or the true NVIS route but it's still interesting to note how the combination of adding radials and lowering the vertical seem to make a big difference. Perhaps if I finally pick up an antenna analyzer I'll be able to figure out what's really going on. In any case I think I'll have to measure out the yard to figure out what can be done with the available space.

In my early "hamstick" experiments I found a radial length of 17 feet and 6 inches worked well with all Hamsticks  down to 15 meters and folded in half worked for 12-10-and 6 meters. Diminishing returns prompted to stop at 4 to 6 radials.

A vertical antenna  uses GROUND as the 'other half' of the antenna (NOT THE RADIALS)and so an elevated vertical is not effective. IT SHOULD BE AT GROUND LEVEL as hardware permits to be most effective. SWR is not the way to best judge antenna tuning  ,it is just easy.
A vertical antenna has an impedance of about 32 ohms and so 1.4 SWR is about as good as it gets for a tuned vertical.
The reason that more radials help your antenna is due to your elevated feed point. But this review has really gone off subject...my apologies.

With a bounce off the ionosphere as your first objective,antenna height only effects antenna effectiveness and with verticals half of your antenna is the ground. Keeping the VERB in HAM...

[armymars]

The best way to tune any antenna is for maximum current. Then match it to the feed line and repeat.

[Carl]

The best way to tune any antenna is for maximum current. Then match it to the feed line and repeat.

I used to use a light bulb to tune also,I was taught 'old school'..You could feel the heat from my home brew radio also would put a spark to your lip if too close to the Microphone.

I now adjust tuner by ear for maximum 'sparkle' and the TX to test my ear. Many people should learn to trust their ears.