End Fed Half-Wave Antennas - Tips and Tricks

[Music] well hello and welcome my name is peter waters g30jv welcome to this video channel today i'm going to talk about n-fit half-wave antennas now i've spoken about nfed halfway antennas quite a bit on this channel but i make no apologies because it's a very interesting very useful antenna and here we are beginning of september some nice sunny weather forecast is pretty good for the next few weeks i believe but it is a reminder it should be reminded to you that we are coming up to the winter and the september month and the month of october are great months to do antenna work so let's uh have a look at the input halfway of antennas and tips and tricks but first of all let me remind you the enfit half wave antenna is a length of wire which is a half wave length on the lowest band so let's say for example 40 meters it's 66 or 67 foot long that is connected to a 49 to one transformer and that transformer is then connected to your transceiver with coax cable so you only need to short length of coix cable to go from this transformer battery transceiver you don't need a long length of coax cable to feed the dipole which means to say no hanging coax cable halfway down the garden and the good news is that you don't need an antenna tuner now that should be great news for those that are going to have or have got an order the ic705 because as at september 2020 or the beginning of september 2020 the ic705s have not arrived but anyway for those that are waiting for the ic705 give this some thought because it's a great antenna but i've headed this video tips and tricks and what i wanted to do today is to cover some various topics that may make the antenna more interesting for you to use may enable you to fit it into a smaller garden may encourage you to go out and use it portable so let's take a look at the options that are available the first tip or trick i'm going to cover is how to convert a an infant half wave that covers 40 through to 10 meters in other words a 66 67 foot long halfway how i'm going to convert that so it covers 80 meters without adding much to its length and the answer is that i use a loading coil and i'll put up on the screen now the loading coil in situ on an antenna that i've put out recently and as you can see it's just a simple coil in series with the antenna it's actually attached to the end of the antenna and then there's another bit beyond that which brings it to resonance so how did it work and what happens to the other bands well let's take a closer look at the principle i've used now here on the screen we've got the antenna on the right hand side you've got the 49 to one anon which is the transformer the right hand side feeds back your transceiver the left hand side feeds the half wave antenna in this case is a 40 meter half wave which also works on the harmonics so it works on 2015 and 10. that in turn connects to the loading coil and beyond that the resonated section for 80 meters now here's a close-up of the coil on the right hand side you'll see i've drilled a couple of holes that's to take the strain and on the left hand side you've got the 80 meter resonator wire i've dropped mine down at an angle of 45 degrees but in fact you can drop it vertically that enables you to to keep the space of the antenna as an absolute minimum this coil is also available commercially on our website it's known as the ojv-atk and you can purchase it um all ready to go now in the normal course of events that coil would purely act as a loading coil to lower the resonance of the antenna but there comes a point when if you put enough turns on a coil not only becomes a loading coil but it also acts as a choke and this is the trick if you put enough turns on that coil it will isolate the resonator section the 80 meter resonator section on the left it will isolate that on all bands apart from 80 meters when it becomes a loading coil so what actually happens is that coil acts as an insulator on all bands from 40 to 10 meters but on 80 meters it passes a signal through passes current through and it becomes a loading call and resonates the antenna on 80 meters now there is also an advantage because the normal half wave and fed antenna works on harmonics and if you think about it if you on 80 meters unless you put the resonant point fairly low in the cw section all the other harmonics are going to land much higher and sometimes out of the top of the band the beauty of this is that you can resonate the antenna on 80 meters any way you like simply by adjusting that left hand resonator section so you can resonate the antenna on the cw section or the phone section and it won't have any effect at all on the rest of the bands in other words 40 through to 10 meters will be unaffected now you can wind your own coil if you want to i in fact have used one of our commercial coils but you need approximately 50 turns on a former of about two inches diameter it's not super critical the real acid test is that when you connect that coil to the end of your basic half wave in other words the antenna that covers 40 through to 10 meters it shouldn't affect the resonance at all provided it doesn't affect the resonance it's acting as a choke and then all you need to do is to add a bit of extra wire around about probably three meters in order to bring resonance into the 80 meter band it's all fairly forgiving so if you if you have 49 or 48 turns or 52 turns it just means to say that that resonant section beyond the coil will be either slightly short or slightly longer to make up the difference the main thing is that that coil should not affect resonances on the 40 through to 10 meter band now a number of uh you have um inquired about the um length of the half wave and how it could be made shorter i think somebody was saying well they love 40 meters but 66 or 67 foot of wire is just too long uh to take around with them when they're operating portable well i can understand that because you think about portable operation you think the great outside there's loads of room but very often there's not as much room as perhaps you thought maybe there's a wall in the way the car park's not that big there's a tree that's in a good position for a shorter length longer length well the answer is that if for example you want to operate on 20 meters and that's your favorite band then you simply cut the antenna shorter so that it becomes a 33 or 34 foot length of wire which is which is which is fine but on the other hand if you want to operate on 40 meters and 66 foot is just too long for you well there is a way around it you can actually load that antenna so let's take a look at those options for making the antenna shorter well here's the neat trick if you look at the top antenna there what we do is we shorten the 40 meter half wave in other words the 66 foot of wire we shorten it and insert a loading coil in the center the reason we put the loading coil in the center is because that's when the where the loading call has maximum effect so it needs less turns and the number of turns you put on there is really arbitrary the more turns you put on there then the shorter the antenna is you should be able to get the antenna down to around about 40 feet quite easily i can't give you the exact number of turns and it doesn't really matter the more turned you put on the shorter the antenna just remember of course that you don't want it to act as a choke but um i would think if you put around about 20 20 turns on a 20 or 25 turns on a 2-inch um former you'd be around about 40 feet long thereabouts but it's an experimental um project it will work but i can't give you the exact um details now the uh one below is um even more interesting because what we're going to do here is we're going to have a 20 meter half wave in other words it's going to be 33 foot or thereabouts of wire we're going to add a coil at the end and make that coil a choke um on 20 meters now again i can't give you the exact dimensions but i would and imagine that around about um 30 35 turns of wire on a two inch former and um say around about one and a half two meters a while beyond that and that will give you an antenna that is resonant on 20 meters and 40 meters it'll be full size on 20 meters and it'll be significantly shorter on 40 meters so you could end up with about 40 foot of wire thereabouts covering 20 and 40 and of course the 20 meter section will actually resonate on 10 meters but i've said as i said before you won't work an awful lot at the moment on 10 meters unless it's a sporadic e opening you know one of the bands i really like operating on is 17 meters or 18 megahertz it's a great band because it tends to open up in the afternoon um and provides propagation that doesn't seem to be there on 14 megahertz and i've often worked stateside stations and stations in canada simply by switching from 14 megs to 18 megahertz so it's a great band the problem is that if for example your antenna is tuned to 20 meters how can you make that end fed half wave also operate on 18 megahertz you certainly can't use it by using the normal harmonic relationship so let's take a look at the option there well we achieve this trick by using a tuned trap if you look at the drawing here you'll see that we've got a half wave on 18 megahertz which is about 26 feet that's fed from the 49 to 1 unknown and there's a trap there tuned to 18 megahertz so that traps off that part of the antenna we've got an 18 megahertz trap which isolates the 18 megahertz half wave but that trap will also pass any frequency apart from the narrow bend within 18 megahertz so it will let the 14 megahertz or 20 meter signal pass through and all we need to do then is to add a short length of wire to resonate the antenna on 20 meters you can make your own trap there are details on the internet or alternatively a company called hari h-a-r-i make a range of ready-made traps now when we come to base station operation i know there's it's quite common these days to have short gardens it's the fashion you have bigger houses and shorter gardens which is great for the domestic environment but it's not so good for ham radio but you know the end fed half wave does offer some interesting opportunities you can actually make the antenna fit into quite a small garden so i'm going to take a look at that now and do some pretty crude drawings on the screen so you can get some idea of what the options are well here we see the familiar inverted l configuration the antenna on the left we feed at ground level and the antenna on the right we feed in the air in both cases the total antenna length is 40 feet which is quite a reasonable length and if you have a really small garden here's a way of getting a 40 through to 10 meter antenna into a length of around 26 feet and what about the radiation pattern of an infect half wave well it's very similar to a dipole and i'm going to put up on the screen here some shots showing you the radiation pattern of the antenna based on a 40 meter antenna but the principle applies whether the base band is 40 meters or 80 meters well here on the screen you see the four bands and it's the dark solid lines that you want to take note of which gives you the basic pattern of the antenna and working clockwise first of all we got the 40 meter section which is a half wave dipole then on 20 meters the antenna becomes a full wave and on 15 meters it becomes one and a half waves and on 10 meters it becomes two full waves and it's quite interesting to see how the pattern changes these patterns are derived from the antenna in a straight line but as soon as you start to bend it of course it modifies the pattern and basically as you bend the antenna so it becomes more omni-directional but it gives you some idea of how the pattern works and how it may favor certain directions in your particular location there is a slight skewing of the radiation pattern which is not shown here but basically the lobes tend to skew sight slightly away from the feed point so the lobes are biased a bit towards the end of the antenna more than at a 90 degree baseline angle the matching transformer is quite easy to make i've done a video on that as well and you can take a look at that but alternatively there's some commercial balance available some questions often asked what about the earth do you need an earth no you don't need an earth do you need a counter poise no you don't need a counter poise what about the what about a line isolator well yes i would recommend a line isolator that's standard practice as far as i'm concerned i always use a nice line isolator right at the point where it goes into the transceiver not the other end because that will cause problems particularly with an n-fed half-wave but put the line isolator at the point at which it goes into the transceiver that will make it very docile it'll have no problems and because you've got a line isolated there your swr readings are likely to be much more accurate than they are without a line isolator because swr meters are quite sensitive to rf on the outside outside of the sheathing so my recommendation is use a line isolator i've used them without particularly for portable i don't bother but for home station use i would recommend a line isolator so there we are i hope i've covered um enough tips and tricks for you to have a go at building or installing your own enfit halfway as i say there's commercial ones available you can build your own great antenna for the smaller garden great antenna for portable operation in both scenarios it works extremely well and i would encourage you to give it a try so as usual these videos i do appreciate you watching this video i hope it's been helpful please remember to press the subscribe button so that you'll be alerted to other upcoming videos in the meantime enjoy your ham radio take care speak to you soon [Music] you

Channel: watersstanton

Views: 132,205

Keywords: End Fed Half-Wave Antenna, Ham Radio, Waters and Stanyon, Vibroplex End Fed Antenna

Id: PKJ77POxQdE

Length: 17min 48sec (1068 seconds)

Published: Wed Sep 02 2020