44 foot Doublet Antenna

Hi All,

Hope you're all keeping well.  


I've found myself in the situation where I no longer have any antennas at all so having to start from scratch. VHF/UHF won't take long to get sorted again but I'm not in a 'perfect' world where I can reinstall a HF fan dipole in my loft so looking at alternatives.

The obvious choice would be a one wire multi-band solution that would be easier for a volunteer to help me with.

I considered a doublet pretty much from historical memory but did remember a shorter doublet for 40m to 10m, so considering that I have no real interest in 160m/80m this might be ideal. A scan around t'internet turned up the following details that look interesting :-

http://webclass.org/k5ijb/antennas/Only-one-wire.htm

My old homebrew Pi-Network ATU will no longer be of use but shouldn't take much to convert it to a Link Coupled Tuner or maybe construct a Z-Match type affair.

It all looks good on paper but thought I'd throw it out there to see if any of you utilise such an antenna setup or know anyone that does. Essentially I'm after a bit of input/help regards performance of such an antenna and maybe details of matching, whether you've used 450 or 600 ohm ladder line etc.


Any help or words of wisdom would be much appreciated and give me the incentive to pursue a course of action.
(Want to get it right as I'm not up to multiple antenna attempts anymore. )


All the very best,
Victor

For simplicity an end fed wire takes some beating. No ATU required either. For whatever irrational reason I just do not like the idea of ladder line coming into the shack and so a doublet or G5RV type of antenna has not been something I've tried.

Lots more info on multi band, no tuner end feds --> 

Hi Roger,

Not exactly what I was asking for but thanks anyway. I'm sure the link you provided will come in use for anyone looking for end fed antenna solutions.  


All the best,
Victor

Wish I could give words from experience Victor, but have never used a G5RV or similar type antenna. Have been using ladder line this past year, but as elements not feeder. Too much metal work in my loft to try and use and even in the garden it would be problematic from the house to the end of the garden.. window frames, rabbit run, trampoline, shed, plant hangers, wife's garden lights.. all made of metal or have metal in to avoid.

I know you don't want to go through multiple tries of different antenna types now, but as Roger has said (and I am sure you know) an end fed wire can work well, either as an efhw for some of the bands between 40m and 10m with no tuner or a random wire for all bands (tuner probably needed to bring swr on some bands to better levels). With one end up a few metres THIS one has worked well for me (it's what was used on on the CT 40m Boxing Day net), and have had contacts on 40m and 20m just with the wire along the top of the fence (when neighbours have been out) and that is very low to the ground. It might be an idea just to deploy a simple wire on a fence (or similar) fed with coax whilst you look into and plan a doublet?

Hopefully someone here has used one and can furnish you with some answers.

Hi Neal,

Thanks for the input, I'll continue looking into it some more. 
Unfortunately due to my limited mobility my options are few and volunteers become less forthcoming if you request their help on multiple occasions. I've slung a bit of wire out of the window for a bit of SWL for now but can't really do anything until the scaffolding has been removed. (Blocking both exits front and rear at the moment!)


All the best,
Victor

Hi Victor, I thought you were interested in 'stealth' antennas hence the previous loft dipole. I think a doublet with a length of ribbon feeder flapping around is likely to attract a fair amount of interest compared to a simple end-fed wire.

End fed half waves and doublets seem to have similar efficiency and we know the radiation pattern is a bit of a mess on other than the fundamental frequency. Doublet requires a tuner, efhw requires a 49:1 coupler and no tuner. I like simple

I forgot to say, the ladder line will have to be routed very carefully avoiding anything metallic. Tuning is likely to be moisture dependant too. I have read that RF in the shack can be a bit interesting with open feeders too.

Not a problem Roger and again thanks for the input.

A lot has to do with practicalities, there's my limited mobility, a volunteers willingness, (which usually means less physical strain and not much antenna knowledge), amongst other things. I could go into all sorts of details such as neighbours stating the fence is theirs etc. etc. but we'd be here all day.

I'll figure something out to suit my circumstances but was just trying to get some input specifically with doublets, ladder line feed and tuners. The tuner isn't an issue as I can build one for myself rather than shelling out stupid money for a commercial affair that tacks a toroid on to 'sort-of-do'.

The pattern plots in the initial link I posted look favourable especially with the shortened 44 foot version so probably worth pursuing. RF back in the shack can be just as likely on coaxial cable and the choice of ladder line is purely down to reducing losses. (That's often argued about immensely in the Ham world too.  )


Ham radio is one of those weird hobbies where other suggestions comes to the fore rather than what was asked. A bit like asking for directions to London but instead being directed to Birmingham because they believe it's a better place.


Thanks again for the time.

All the best,
Victor

I've worked on multiple random length doublets.  Some lengths are harder for antenna tuners to dial in that others.  The best advice I've seen for tuning in doublets is to keep its length as far away from resonance multiples on as many bands as possible.  Most people these days see resonance as being low impedance (i.e. 1/4 wavelength), or easy to tune, but it also will have a naturally very high impedance (or hard to tune) half wavelength multiples.  1/4 wavelength easy to tune impedance on 20 meters will be the same as 1/2 wavelength hard to tune impedance on 10 meters, making one of the bands possibly not use-able.

With the setup of antenna tuner -> parallel feed line -> antenna, unlike with a coaxial setup between the radio and antenna, adding and removing length of said parallel feed line is a legitimate way to adjust the antenna system to be tunable on all the bands you want to use.  The reason is both the parallel feed line is not being fed with its characteristic impedance, nor is it feeding the antenna with its characteristic impedance.  In this case, the feed line itself, in addition to carrying the signal to to antenna, is also acting like an impedance transformer in and of itself, and thus, is actually part of the matching circuit of the antenna.  The way to change the impedance a parallel feed line is presenting is... changing its length, this can make some bands more tune-able, but can also remove other bands from being tune-able at the same time, so it can be a double edge sword.

When it comes to running parallel feed line, it is fine to run it past metal, you just don't want to run it along anything metal for any real length.  Try to keep any metal said wire passes as close to 90 degrees off of the direction of the parallel feed line as much as possible.  This is for the same reason of horizontal and vertical polarization, and how little they interact with each other.  You definitely don't want to run said feed line along the same direction as a metal pipe or electrical wire or losses will occur in the form of capacitive coupling.  This causes RF interference not just in the shack but elsewhere in the house, depending on where said metal is run and what it comes into contact with.

If just running a story or two it is fine to run parallel feedline straight up a wall to an antenna in the attic.  If running for longer distances, once outside, it is best to keep it twice its diameter away from as much as possible.  When it comes to running in the same direction as other wires, I try to increase this distance by four times when possible, but that is jsut me, I have seen successful installations with less distance between the parallel feed line an another wire going the same direction.  PVC/CPVC and most plastic is good to use an stand offs in such a situation.  Burying it is also not a good idea as the earth will absorb most the the antenna's RF.

When it comes to tuners, you have already figured out that anything that presents a balanced output without the need of a balun tends to be the best.

I think I've covered most of what was talked about, any further questions?


The DB

Sir, I tip my hat to you with much thanks for your time as well as obvious wisdom on this subject.  


This has reassured me to continue treading the path I have started and all I ever wanted was some first hand practical experience or advice to ably assist me which you have fulfilled immensely.

Much is written about these subjects, a lot has been re-hashed over time often with consequential losses or errors and very few of the founding radio enthusiasts or those who learned from them still have a voice to personally verify such knowledge.

I say with confidence that we do truly stand firm on the shoulders of giants giving thanks to all the radio enthusiasts that came before leaving us with the legacy of radio we still enjoy today.

With a very big thanks to those few left that can still impart such valuable information today.


My very best wishes and regards to you,
Victor

Hello Victor,

just an idea have you thought about making or buying a Magnetic Loop Antenna
the one from ebay pops up on hamradiodeals time to time  https://www.ebay.co.uk/itm/304280391416?hash=item46d8864ef8:g:b5MAAOSwE8VbzeFN
Or better still you can buy the parts and make it your self, i gather that you like making things.

Hi Tony,

Weirdly I had dug out my old magnetic loop to maybe set up temporarily but I'll be damned if I can find the variable capacitor that went with it.....typically packed away to keep it safe but don't remember where!

From what I do remember although it worked it wasn't all that great but definitely better than nothing.
My homebrew soft copper pipe version was definitely cheaper than a purchased one that's for sure!

Excitedly gathering components for a link coupled tuner at the moment so should keep me out of trouble.


All the best,
Victor

Not a problem, any time.

Feel free to experiment, in fact I encourage it.  If you limit yourself to what I call a "coaxial mindset" (that is many of the ideas the people who have only ever used coax have) you will likely have a poor performing system.  Feel free to question whatever you think you know on the subject, and have fun.


The DB

Try a inverted V in loft regards shep 289

Allshep wrote:

Try a inverted V in loft regards shep 289

Hi Allshep (sorry don't know real name). Not wanting to step on Victors toes and speak for him, but just a note as I've noticed your reply to say that an inverted V can work very well as a loft antenna. Victor and I have used singularly and in fan arrangements. But unfortunately he cannot use that in that location now and so the reason for asking opinions on the 44' doublet.

As I understand it, a 44ft doublet might work on all bands 160 to 10m with a 4:1 Low Power Balun with a tuner, as long as you use no more than 10 Watts.

Here's the link to self build the Balun



I know you like construction Victor, so this would appear right up your street.

Hi Wayne,

You can probably impedance match a straightened paperclip for 160m but unfortunately it won't be a good antenna. I've heard not dissimilar claims for shortened antennas and another one of the reasons I've decided to limit myself with a 40m-10m antenna system.

Allen Baker himself admits to never 'perfecting' the balun and in his example he attempts to tame the high impedances that could be faced to work with his autotuner. As suggested it should only be used for low powers as the ferrite will very quickly saturate so is already an obviously lossy system. I'm doing my very best to avoid any 'iron' in the antenna system at all.


Many thanks though to yourself and others for your input to my query, it is much appreciated that Charlie Tango members have tried their best to help and offered suggestions.


I've gathered most of the components for a link coupled matcher now and started construction on some ladder line as well as test equipment construction to ensure I achieve balance. Hopefully it will mean a volunteer simply has to 'hang' the antenna for me and everything works first time. 

As you mention I do enjoy homebrew construction and so far having immense fun with it all, this only came about due to losing my antennas and looking for solutions that fit my needs. If I can work some inter-g or shoot a bit of skip with it on the up ramp of the solar cycle, (past the inevitable Italian Kilowatt beams!  ), then I'll be more than happy.


All the best,
Victor