G7FEK Limited Space Antenna: Part 1- Introduction
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- Опубликовано: 28 авг 2024
- Going over how I went about constructing and fitting the G7FEK Limited Space Antenna on my small suburban lot. I live in a rental property so I've gone about the installation in such a way it can be put up and torn down in a hurry.
This antenna basically is quarter wave inverted L's on 40 and 80 meters. Full-sized quarter wave elements on 30 and 20 meters.
It all comes off the one feedline. Impedance allows for automatic antenna switching.
G7FEK website: www.g7fek.co.uk...
G7FEK detailed PDF: www.sral.fi/tur...
Hi Andrew. Great to see another build of my antenna, great job, more thorough than my usual portable lash ups!!
There's a couple of points Id like to share, just for the benefit of other constructors who see your video....
1) The extra element you have for 30m is not normally needed as the top is already a resonant half wave near end fed OCF, at or just below 10MHz, and is matched via 1/4 wave transformation effect of the vertical section (like the ZEPP). A counterpoise just shorter than a quarterwave on 10MHz (about 7m) is usually sufficient to get this band working well on 30, although an ATU is usually advisable to null out any inductive reactance present (there will be some). I think you needed this extra element because you have the antenna in a corner configuration with a very acute angle. This a great space saving idea and teh antenna works well in the corner of a plot, but narrower than 90 degrees, this effectively shortens the electrical length of the top on 10MHz by folding the top back on itself. It will affect 30m to some extent, but it should work fine on most other bands though.
2) The feedpoint does not have to be elevated. It can be at ground level. Trying to find that extra bit of height might be a problem for some people, so I just thought I'd point out that it is not necessary to elevate the feedpoint, raising the far ends of the radials for at least the last few meters is essential though. Radials should be insulated wire (2.5mm2 electrical wire works OK, but thicker is better). Other ground systems can be used alongside, or instead - even a simple ground rod if soil is conductive enough.
3) The minimum number of radials is two (one for 3.7 MHz and one for 7.2 MHz). This will get most bands working and probably all bands if you use ATU to trim reactance. Others radials are optional, but improve performance and matching for sure.
4) I recommend a choke at the feedpoint, especially if you skimp on the ground system. The RF return current will take the easiest path to ground, even if it is via your radio and house supply!. You can use the coax outer as an extra radial by placing the choke at 1/4 wave away from the feedpoint on the chosen band. A simple and effective choke is 10 turns of RG58 on FT240-43 toroid. 22ft of RG213 wound around a plastic drainpipe works very well.
5) I love the idea of the high inductance DC shunt to remove any static charge. This will also offer some protection for the radio front end if you forget to unplug it before a thunderstorm. I'll start recommending this to other users and give you a credit!. Static isn;t usually a great problem at 24ft, but it will certainly help.
All in all, almost everyone who has tried the antenna has had great results in getting almost all amateur bands includign 80m. The four main ones without needing ATU, in a very small space and without the usual extreme compromise on 80m. That's what it was created for and 80m is an essential band in sunspot minimum!!. You always get some jerk who will say it doesn't work multiband or on 80 because they "modelled" it or whatever, but the original was built from pen and paper and tested in the real world by hundreds of Hams. Enjoy.
As you are doing so well with local contacts, DX on 80 should surprise you even more as the peak angle of radiation is quite low, towards the horizon on all bands. It can often beat a full size dipole at same height for DX on 80. Looking forward to your nighttime DX video, lets hope for a good opening!!.
All the best. Mike. G7FEK.
Hi Mike,
I am truly humbled by your extensive response my friend and was hoping you would see my videos. I had you in mind when I was making them and wanted to see your response/advice. I was going to message you when I had a few more posts up but you beat me to it :)
I've pinned your response and will make sure it goes on all future postings. And re the points you've made.
1) re: 30m element. I probably should have tried adding the counterpoise before going to the trouble to add the 30m element. When I've made up the fancy little junction box, it will be much easier to disconnect and experiment with things. Funnily enough, I've found the performance on 17m to be amazing and no tuner needed at all :) Having the top sections angled the way they are was the best I could do in my yard, but I probably could get another fibreglass pole and move the whole thing to another area to do it the correct G7FEK way, my block is 45 metres long, just don't have trees in the right place which makes it a challenge. No tuner is also needed for 15m btw.
2) re: elevated feed point. I was a little paranoid about the metal fence right behind the antenna and wanted to ensure I wasn't wasting my RF or getting unnecessary reflections, otherwise yeah, it would have been much easier to keep it lower to the ground. I've only got skinny hook up wire, I'm going to strip some electrical leads so I can make it stronger, better harder, more visible (sounds like Daft Punk lol)
3) re: radials, yeah I found adding the 30 and 20m radials eliminated the need for a tuner.
4) love the choke Idea, I'll be building that one :)
5) you're too kind mate, thanks for the credit on the DC shunt, I found it made anywhere from 1 S point to half an s point of difference re static. Sometimes more depending on what sort of day it is. It's the same with my 40-meter quarterwave ground plane.
This antenna is now my weapon of choice and will always be the first thing I throw up in any new QTH. I'm thinking about making a portable version as well. If I didn't need the fibreglass poles and had big trees, it would be an amazing stealth antenna as well :)
I've already made one DX contact on 80m and will post that video soon. As I make more, I will post more videos. I need to motivate myself one of these mornings soon to come out to the shack before dawn. In Australia right now, the 80M DX seems to work better at that time as opposed to our evenings.
Again thanks for your response mate, and thanks for sharing your design with the world.
73 from Andrew, VK2XXL.
I love what you've done to make it work in your particular circumstances. That's what I love about this antenna - having the feedpoint accessible, it makes it so easy to modify. If you put up a 1/2 size G5RV or similar, you're stuck with what you've got (which isn't a lot!). Ham's have been able to use this antenna on all bands from 160m to 6m using various mods and tweaks and for me, that's the fun part of Amateur radio.
Glad you are getting 17m and 15m without ATU. It shows you've done things right. The antenna should work on all of 80/40/(20)/17 and 15 with very low VSWR and often no ATU needed (except to expand band coverage). There's also another dip which often appears somewhere between 27.5 and 28.5 based on anecdotal information, so is sometimes useful at the bottom of 10m without ATU. But with an ATU 10m works acceptably well without mods, especially if you use decent coax.
Once installed it can be a bit techy to resonate because it relies on interraction to achieve low VSWR on as many bands as possible, plus needs attention to the ground system, but then where would the fun be if it was plug and play!!. You downloaded the guide which is a good idea. Many people just find the picture on a blog somewhere. The guide is very useful to understand the antenna.
The proper location is here: www.g7fek.co.uk/software/G7FEK%20antenna.pdf
Love what you are doing. Keep up the good work. Hopefully your vids will encourage others to get off EZNEC and build some real antennas! I sold my house and I'm renting a place at the moment with no antennas allowed, so I'll be making up another one of these for portable work this summer.
73, Mike.
Yes and I didn't even use the Antenna Analyzer which recently turned up in the post! Following your measurements generally got me very close and I only used my SWR meter. Everything looking good later on with the analyzer.
The SWR is pretty flat throughout most of 27Mhz and yep, 10m is usable right up to about 28.5 which makes me happy. Although 10m propagating is hopeless right now as we come into winter. Need the summer to come back for that sporadic E so I can really test her out :)
I found the guide to be paramount.
Video 3 is now online showing a DX contact with W6UC. It's low down, but it worked! All within a few days of the antenna going up :) I'm looking forward to doing many more :)
Shame about the current situation you're in re the rental property. I hope you're out of there soon Mike!
73 from Andrew, VK2XXL
Hi again Mike, just letting you know my 80M DX video is backup. RUclips reviewed and determined it doesn't violate community standards! You can call this an edgy DX video lol. Check my main channel page. 73 from Andrew, VK2XXL
@@g7fek thanks mike for this great antenna! I use it as my main antenna at my QTH(with a few mods). My steel carport does the counterpoise work :)
G7FEK is an amazing antenna. I built one for our QTH. Added the 20m sucker, and between the auto tuner on our Yaesu FTDX10 and a MFJ949D, we can work everything from 80m- 6m. South Africa from EM93 several times.
It's a very interesting antenna concept: it looks like an OCFD, acts like a multi band inverted L, and is classified as a Nested Marconi.
Just build it! You won't be disappointed.
I used 14AWG THHN, 600ohm ladder clips, a pvc reinforcement pole so it's at 25ft, and some random 30ft-ish ground radials.
The plans even include a switchable coil to add 160m, which I have yet to build but need to.
Do it and you'll love it!
73 de NM9X
Fantastic construction ideas and great to hear it's working so well 🙂
HOLY SMOKES. I've been around Ham radio operating for 50 yrs now, I'll have to say that s one Bobby dazzler of a wiring maze.
Thanks for sharing!
Kind regards, Eric Dee.
Haha! It is a mess, but works well. Tidier if you just have the 40 and 80m elements :)
5 people think my construction wasn't pretty enough lol! Thanks for the 79 likes and so far more than 7300 views. This video has done much better than I expected!
I've seen this antenna online some year's ago, I can see how it works thanks to the video.
Thanks for the video and thanks to G7FEK for the design.
Looking really cool Andrew, great job mate!
Hi I have discovered that the G7FEK works on 6m also with a good vswr, 73.
CONGRATS OM, put one.
up hr 2 yrs ago works great on 40/ 80
2 cp on 40 1 on 80 no grd ,no elements on other bands! 😅 cp 3 ft high 73 K9UT
I am just Building the antenna and wanting to take advantage of the Vertical 30M add on. The reason being I'm suffering from QRM from my neighbors and the 30M Vertical add on (Like the 20M) would keep the Antenna elements away from the property next door. Is this a Viable Option ? Would the Transceiver see the Vertical section First? Hope you understand what I mean. Thank you.
Hi there, sorry but I only just saw this many months later. The RF will always flow where the impedance is lowest or closest to 50 ohms so yes. I think that's what you mean. Just insulate from the top with a bit of nylon rope and you'll be right. Experiment and adjust to your situation. That's the beauty of this set up. As you can see here I improvised on the fly and used this for many months :)
Hi, I interested of that noise suppressor. Whats is a wire diameter ?
Hi mate. Wire diameter is not critical. A reel of standard hook up wire from your local electronics store will be fine.
Can you share the design of the noise suppressor please. I too have one of these antennas they work fantastically well.
Sorry only just saw this. Grab some PVC pipe, and do 100 turns of hook up wire. 4x 25 turns up and down. Connect one wire to the radiating element, the other to ground (radial side) and that's it. Mine knocks out between 1 to 2 s points of static. Since I made this video I've also added an RF choke which in addition to stopping RF in the shack, also stops the coax cable from picking up QRM. Both have made the system very quiet!
@@VK2XXL Many thanks for that Andrew
Anytime :)
thanks for sharing and to g7fek ...so not trying to be a smart ass . honest. would it not be better to take the suppressor straight to ground. ??
Only just saw this. Not at all. There's more than one way to skin a cat :)
Nice antenna and explanation ! 73 KB2QQM
Hellow Dru like this video and your choice for this antena was perfect i look to get my 5band dxcc i only need 70 dxcc on 80m i read all info.in the g7fek link he say that take off is about 30 40 greed sorry my english is rabis any away in SA 80M dx is very dificul you need hi power our country big mabe more tha all EU so with bazooka antena make qso with roll coutry and SA coutry as well but to hit EU is another history to make a vertical not easy to hang out 20m poll and 36 radials with 1/4 wave for calum 5m is ok but all book says oposit his theory, i have back yard is abt 15m x15m i have tower 10m and bambo a lot here so i will make this antena like the chocke or uglybalum you make 100 turns with 1,5mm wire is good? and is isolatad whith secion 25 turns ? If you have more info for this choke let me now pls look Dru tks for a very nive anderstud i have just littel questions i have youtube channel and alredy live draw there my call i py1ax hope cat u 73 for now gl
Hi there! Sorry I've relocated over the last couple of months and didn't see this until now. The DC shunt (noise suppressor) is east. Grab a small piece of 2 inch PVC pipe and with thin hookup wire (1.5mm fine but anything will work) wind 4x 25 turns over the top of one another so that's a total of 100 turns. You could just make the pipe longer and do 100 turns straight, but it would be much longer that way. No need for it. Since making this video I got an amplifier and let me tell you now, 400 watts makes an amazing difference! Good luck and let me know if there's anything else you would like help with.
Gostei muito amigo qsl qrv 73
haha not scared of rain then, we would have to wrap the so239/pl239 with self amagamating tape just for summer...
Hi there Steve, we've had some very heavy rain these last few days and honestly, the SWR didnt move at all. I've been running 400 watts on 80m through the antenna, my amplifier has SWR protection built in. No change. I do have the coax all sealed up which is the more important part. None the less I'm about to make up a box which will seal and connect everything together. This was only a quick installation, but I'm pleased to report it's held up really well. I might even make a video throwing a bucket of water over it to show what happens....NOTHING. Different if you have a beam, but the majority of this antenna is sealed wire. Hams get far too paranoid over this kind of thing. Here's a video that proves it: ruclips.net/video/NvPIaLD6B7M/видео.html
will look forward to the video, my daughter lives in nsw and complains of the rain... haha she should stay home then. seriously though, good to see the antenna again, I built it years ago out of a 1/2 G5RV and it did out perform it easily. 73
I've been getting 20 over s9 reports from all over the eastern seaboard. They are pretty awesome and ZL's seem to be calling back at me quite a bit as well. Yeah I'll combine it into an update video I'm about to do which will show the new box once made up. I've also recently added an RF choke (12 turns over an FT-240-31) which has stopped the common modes dead in their tracks as recommended by G7FEK. I put that one into a box, fully sealed with ventilation holes underneath. 73.
Fine !! 73 de lu1ls
Nice build 73 de VK2AOE