How directional is an MFJ-1788 magnetic loop?
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- Опубліковано 8 лип 2024
- A viewer asked me..........does an MFJ loop work better mounted vertically or horizontally?
I mounted the antenna vertically on my mast with a rotator, then did some WSPR tests to find out.
Spoiler alert.........it's nowhere near as directional as I expected!!!!
The Amateur Radio UK channel is run by UK radio amateur M0GQC (James). As the channel name would suggest, the channel focuses primarily on amateur radio within the UK!!! - Наука та технологія
Before I moved I had mine at a height of 2mtr vertical and got into Australia (VK6AL). Antenna was running E/W.
These experiments are what it's all about (for me at least!). Great work!
I think that maybe being 6 or more dB down from the peak of a pattern has less effect than many of us intuitively think, so you only really experience (i.e. properly notice) directionality due to sharp nulls or a good F/B ratio, especially on HF.
I've done a lot of experiments with homebrew loops over the last couple of years and have found that the effectiveness of them versus a dipole or other wire antenna depends on a lot of factors other than absolute peak gain on the polar pattern; for example one antenna will win in the morning and the other at night, presumably due to elevation pattern differences (& this is all for transmit effectiveness - I use an Rx-only loop for receive which means I can devote my focus to transmit effectiveness on the other antennas & not worry about their S/N on Rx).
I've also tried horizontal vs vertical, at heights of 3m and 7m AGL. What I've found (again this is all for transmit effectiveness) is that for 20m band, my 3m circumference (10mm copper tube) loop beats my inverted V at the same height if the loop is horizontal but not if it is vertical. On higher bands, capacitor losses increase (I think - ESR tends to rival capacitive reactance). On lower bands, I've had a 6m circumference 10mm copper tube loop *easily* beat my wire antennas on 80m, but this is because I have little space and the 80m wire antennas are compromised.
But, after a lot of experimentation, I'm coming to the conclusion that a reasonably well constructed loop is approximately as good as a dipole if both are in free space, and one will then win over the other depending on the environment and frequency band at lower height, but probably not by much (YMMV), and convenience is a big factor too.
It's all part of the fun!!
Some great points there.
As you point out, 6db probably doesn't make as much difference as most of us think. Let's face it, 6db is approximately one s-point. The QSB can have a greater effect than that.
Another influence with WSPR is the stations hearing and reporting your signal in various parts of the world. I tested an antenna the other day with WSPR and none of the stations I heard reported hearing me and we were on similar power levels. Magic this radio stuff.
Thanks for your report James. I live in the east bay San Francisco in a highly restricted HOA. I have an attic dipole and it transmits well, but too much noise for receive. I have two outside receive only active mag loops outside for receive which are phased through T/R switching unit (DXE NCC-2); one loop is 8 ft off the ground in the garden, and the other is on the roof about 20 ft. high. I got the 1788 to see how it compared to my receive mag loops sensitivity. The 1788 did better than the active receive loops, and, it transmitted almost as good as the attic dipole. My 1788 was mounted vertically, 8 ft. off the ground on a rotator. My plan is to mount the 1788 horizontally on the roof and see how that works. The biggest downfall is the extremely narrow bandwidth; tricky to tune. I use the band scope on the IC-7300 to get close. '73 Bob
I have my 1788X mounted horizontally 24 feet up and it seems to be omnidirectional. Propagation / time of day is certainly a big influence. Re. the tuning : I am using an FMJ 212 Matchmaker which makes moving a few kHz up or down less of a faff as you can both hear the very narrow 'null' and see it on the waterfall by just 'fine' tuning. Plus is you don't need to Tx and risk high SWR between bands, or in so doing, interfere with other operators by sending out a long carrier. A seemingly less considered factor when deciding between vertical and horizontal, at height, is the wind. In a vertical orientation it would catch the wind like a sail. I still get anxious in medium to high winds even with mine being horizontal !! It's a fine antenna, once you get used to it but definitely not cheap.
Well, you offered me data to pour over. You are correct, it does work. I stand corrected and I am glad I followed through on your insistence. Thank you for providing the your point. I appreciate your time. N4KBM
Good experiment! Your findings are pretty consistent with the other videos I have seen testing the MFJ-1788. It seems those who are using this antenna for strictly digital modes are quite happy with it. Those using it for SSB phone contacts are not impressed with it. Either way if your circumstances, such as living in an HOA antenna restricted neighborhood, do not allow visible antennas then this may be ones best hope to get on the air. It can be ground mounted vertically as little as 1 meter high disguised by plants, shrubs and trees with fair results. If only it weren't SO expensive! Now subbed. 73!
Thanks for subscribing, great to have you aboard! Your comments sum it up very nicely.
The bottom line is that it is a compromise antenna. It's not going to keep up with a full sized antenna, especially at the lower end of it's coverage (30m & 40m).
From 20m upwards it doesn't do too bad when compared to a dipole. It's certainly less directional than a dipole. MFJ say that it should come close to matching the performance of a dipole. I'm slightly on the fence with that claim!!!
I haven't actually tried it ground mounted. Could be an interesting experiment for another video!
Based on your findings and what I’ve speculate . I Think 💭 it’s probably best horizontal just like a dipole .. I think it’s a lot better though than a dipole . But as we also know vertically antenna with 45” degreee angle to 15” angle are aimers for ionic- sphere . But base on your findings it shows that horizontal is at best . I’m stick with that and place mines also horizontally.. 73
How it works on 11 meters cb band?
This is the 1788 version which covers from 15 meters down to 40m, so won't tune on 11 meters CB.
However, if you get the 1786 version (which covers from 10 meters down to 30 meters) then it should be usable on CB. Obviously you sacrifice the ability to use 40 meters with the 1786 version.
Don't use a mercator map for directional study. Use a gnomic protection based in the UK
🤦♂️
hi james, i just came across this video, after just working m0lrq peter on 40m cw, with his 50w. so i started to research this ant. bit surprised by different peoples results hi, peter had his loop 2m above the ground, so i am a bit confused by his great results. just thought i would let you know my findings , and i will find your pervious videos about this loop, so get more info. cheers james, take it easy mate, have a good weekend. 73 brian zl3xdj
Hi Brian. Wow, that video is a blast from the past. One of my very early videos which I'd completely forgotten about!
There's some really mixed reviews for this antenna online. People seem to either love it or hate it. I think it comes in for some fairly unreasonable criticism to be fair.
MFJ say that it's equivalent to a dipole. My personal perception from using the antenna is that this was true on the higher HF bands (20m & higher) but it's a compromise on 40m.
As for height above the ground, I mainly used mine on the upper bands (20m & above). I personally found that I got better results with it elevated as high as possible. I live on a fairly built up housing estate which is also surrounded by several big warehouses, so plenty of clutter on the ground to attenuate your signal.
It could be the case that for NVIS on 40m, it might actually be better closer to the ground?
My biggest gripe & a massive pain in the backside with this antenna is having to constantly re-tune every time that you change frequency, which drove me to total insanity! This is the main reason why I would choose a full-size antenna over this loop if I had the space.
If data is your thing (such as FT8 where you tend to stick to a fixed frequency) then it's a great option for limited space, and actually not that much of a compromise.
You have to judge it for what it is.
@@AmateurRadioUK thanks for all the info, and as you say it's probably a compromise ant, that's why iam really surprised that m0 station running 50w with the ant 2m off the ground is getting through to me on 40m cw, I can't really understand how that is.
Anyway qrt here due to big thunder storms, wow the sky is going crazy hi.
Have a good weekend mate, cheers brian zl3xdj.
So horizontal, and no need for a rotator?
That would be my approach. I'm currently having a bit of a re-shuffle with my antennas at my home QTH. When this goes back up I will be mounting it horizontally again.
Unless you have a specific reason to mount it vertically..........such as a need to try to reject local interferance (using the nulls of the antenna), I personally would just mount it horizontally as high as is practically possible to do so.
I note that the null on either side of the loop is very narrow at "approximately 15 degrees" (according to the MFJ manual), which means that when mounted vertically you are still getting 330 degrees coverage, or more accurately 2 "lobes" of 165 degrees in each direction.
Even mounted vertically it is still essentially omnidirectional. This may not be technically true due to the small nulls but even MFJ state in the manual that "a small loop antenna is essentially omni-directional with the exception of two small nulls".
My personal experience with this antenna is that the nulls are so narrow that in practical terms it made no noticable difference.
These videos on the MFJ loop are getting quite old now...........they were made well over a year ago so I'm struggling to remember exactly what I said in the video. I might actually have to sit down & watch my own videos to remind myself!!!
Having said that, they do still seem to attract a lot of views. It might be time to think about doing a revisit on this one if I can think of something different (and also interesting) to do with it!
Jesus, dude, why is your intro/outro music, like, 5x louder than your other audio?? Have mercy on those of us listening with headphones!
Jesus, dude, why don't people, like, look at the date the video was published before commenting on a video which is over three years old?? Have mercy on those of us who took a chance & opened ourselves up for all sorts of criticism when we had to learn this UA-cam lark from scratch!
Hey FlapFlake, hope that loud intro shook some of the wax out of your lug holes? James is a great guy, running a great channel. He's putting himself out there in the public domain to share his experiences and offer advice to a host of folk, which seems to be a whole lot more than you've ever done.
This video is three years old, you've got some catching up to do.