unun info.

[pjm0bhn]

Hi all,
I have just started to get my shack back together after a 4yr break.
After buying my radio & other bits & bobs my budget as wittled down to virually a few quid,due to this fact i have not much choice but to try one of these unun's as i can't afford a sgc tuner at the moment.
I used to have a tower & 4 ele quad but alas this is no longer possible.having never used a 9.1 unun i am not sure how best to set it up for my location,my garden i 50ft long & 15ft wide,at the the far end i have a 26ft steel pole isolated from ground mounted on brackets to a brick wall,at the shack end i have a height of 28ft to the house guttering & facia board.

Ideally i would like to work from 80 to 10 mtrs,would this be viable using a 9,1 unun? o.k i know this will be a comromise but at the present time this seems to be my only option considering my low budget.....Any idea's anyone,all replies welcome wether they be positive or negative.

Cheers
Paul M0BHN.

[coffindodger]

hi paul, what feeder are you planning on using for the antenna and do you have an atu?

might sound a silly question..

billy

[pjm0bhn]

Hi Billy,Thanks for reply,Well at the moment i only have the fc-30 to the ft897,hence the need for a 9:1 unun.
As for feeder i have about 90 to 100 ft of 50 ohm's coaxial cable and about 28ft of 450 ohm's ladderline.got loads of plastic covered wire & 100ft of open wire flexi weave.

The unun will only be a short term thing till i can get a bit more cash available,so will have to rig something up with what i have for time being.Never really bothered with 80 40 mtrs in the 13 yrs i have been licenced always used 20 to 10 mtrs,so will be new to me really.

Cheers
Paul.

[coffindodger]

not bad space wise, how far to your shack from the facia board antenna support..

im only asking because thats not a bad situation for an antenna..

[steveeh131047]

Paul,

In my view you have plenty of better options than using a 9:1 impedance transformation. As Billy has said, you have quite a useful space to work with.

Here's a couple of thoughts:

1) A ZS6BKW dipole with "drooping" ends. 50ft top between your facia and pole with 21.5ft dropping vertically at either end. Centre feed it with 44ft of 450 ohm line and you'll have a good 50 ohm match on 5 HF bands. Feed it with any length of 450 ohm line and use a wide range manual tuner and it will perform well on all HF bands - 80m up.

2) Use the 26ft pole and 28ft of wire coming back towards the facia as a "half-size W3DZZ inverted L". Place a 40m trap in the horizontal wire 6ft along from the pole. Feed between the bottom of the pole and a good earth system with 50 ohm coax. That will work well on 80m, 40m, 20m, 15m and 10m.

Apologies if I have misunderstood your set-up.

Oh, and keep listening to Billy who is leading you in the right direction :)

73,
Steve G3TXQ

[pjm0bhn]

Originally posted by coffindodger
not bad space wise, how far to your shack from the facia board antenna support..

im only asking because thats not a bad situation for an antenna..
50ft to wall under facia board & 49ft to the actual facia itself Billy,these are the actual measurments from where the support pole is mounted to the boundry wall.

Paul.

[pjm0bhn]

Originally posted by steveeh131047
Paul,

In my view you have plenty of better options than using a 9:1 impedance transformation. As Billy has said, you have quite a useful space to work with.

Here's a couple of thoughts:

1) A ZS6BKW dipole with "drooping" ends. 50ft top between your facia and pole with 21.5ft dropping vertically at either end. Centre feed it with 44ft of 450 ohm line and you'll have a good 50 ohm match on 5 HF bands. Feed it with any length of 450 ohm line and use a wide range manual tuner and it will perform well on all HF bands - 80m up.

2) Use the 26ft pole and 28ft of wire coming back towards the facia as a "half-size W3DZZ inverted L". Place a 40m trap in the horizontal wire 6ft along from the pole. Feed between the bottom of the pole and a good earth system with 50 ohm coax. That will work well on 80m, 40m, 20m, 15m and 10m.

Apologies if I have misunderstood your set-up.

Oh, and keep listening to Billy who is leading you in the right direction :)

73,
Steve G3TXQ Tnx for info Steve,i was thinking along the lines of option 2 but the boundry wall actually supports the 26ft pole and is a little close to an allyway to the rear of public garages,so i am reluctant to feed the pole.
The idea of a unun was for a tempory solution.i first tried a linear loaded dipole made with ladder line but next door neighbour took an instant dislike to it.

Paul.

[m3xkm]

i made the end fed w3dzz it worked very well,i had it fed with the un-un i used it for quite a few months with good results ,i found that if i put counterpoises on its even better.i posted a diagram of the sizes a few weeks ago.it was in practical wireless in 1994,u can also add an 80m coil to make it resonant on 160.

[pjm0bhn]

Originally posted by m3xkm
i made the end fed w3dzz it worked very well,i had it fed with the un-un i used it for quite a few months with good results ,i found that if i put counterpoises on its even better.i posted a diagram of the sizes a few weeks ago.it was in practical wireless in 1994,u can also add an 80m coil to make it resonant on 160.
Thanks for info.i will look it up,i have already made my 40 mtr trap so its just a matter of measuring the radiating eliments,i have plenty of wire for counterpoise.Can't really see the need to feed with unun though.

paul.

[steveeh131047]

Paul,

I agree - there should be no need for a UnUn.

I wonder what trap component values you used - "any old" 40m trap wont necessarily work in the W3DZZ design.

Steve G3TXQ

[pjm0bhn]

Originally posted by steveeh131047
Paul,

I agree - there should be no need for a UnUn.

I wonder what trap component values you used - "any old" 40m trap wont necessarily work in the W3DZZ design.

Steve G3TXQ
I Made this one lastnight steve hope its correct?
Paul.

[coffindodger]

hi paul, i made a full set of coaxial traps which seem to work well. i think though to use it on the W3DZZ design it will have to be "tuned" to work as it should on that particular antenna design ( that is of course if your going to stick with the dimensions of the original)

Example, the original design and dimensions may use a trap "tuned" at say 7.050 so the dimensions of the wire will corrispond with this. i think this is what steve means when he says any old 40m trap wont do..

i made all my traps on the same size former going against some designs and i didnt butt my coax turns close as i found there wasnt room for moving the coils to tune the trap, the former size didnt make that much difference ( all on 43mm OD pipe) and having the room to move the coils made it a breeze to tune to whatever bit of the frequency i wanted.

one tip is do any sealing of joints ect before tuning as to my costly mistake (time wise) on my first attempt was i tuned them all,secured the turns on the former then sealed and all were out when i tested them.. having run superglue down the coax coils it made it hard to undo so threw the lot..and started again..

now though i could do em with my eyes closed..


i made a lighter one by using a toilet roll tube with 3 strips of plastic stuck to it ( like little plastic lolly sticks) made the coil sticking the turns to the sticks and when it was made took the cardboard former away so it was like an air wound coil. this worked fine on testing ( for tuning) and was much lighter which is an advantage if using a few traps on an antenna design.. iv not got a pic on the computer of that one..

The W3DZZ seems a pretty popular design and seems to get good feedback so this may be worth a crack at..

below is one of my 10m traps.. not a pretty sight but they work and are cheap..

billy

[m3xkm]

that is the same trap i made with 11 turns of rg58 coax,it worked ok for me i had no need for a tuner on 80 40 as long as the wire it trimmed correctly,only needed the tuner for 15 17 20m.also i added the 80 trap with 20 turns or rg58 also i did not need a tuner for 160,it had 8.54m of extra wire from the last trap.on 160 80 40 the swr was below 1.5 and resonant througout the 3 bands.

[steveeh131047]

Originally posted by coffindodger
i think this is what steve means when he says any old 40m trap wont do..

Perhaps I should have explained :)

You can build a trap dipole that works on 40m and 80m with a wide variety of LC combinations for the trap; they just need to be parallel resonant at 40m, and then you can adjust the length of wire outside the trap to get the 80m resonance.

But, for the antenna to then also be resonant on 20m, 15m and 10m requires particular wire lengths in combination with particular values of L and C in the trap.

For example a 40m trap comprising a 22pF capacitor and a 23uH inductor would be fine for a 40m/80m dipole, but it wouldn't give you the other 3 bands.

The ARRL Antenna Book shows a design using coax traps which has 32.3ft inside the trap, and 21ft outside the trap. The traps are 8.75 turns of RG-59 close wound on a 2.375" former and are tuned with a dip meter for resonance at 7150KHz. They also show a "dangling" 6ft length of wire positioned 4.9ft outside the trap which permit a bit more flexibility in adjusting the resonant frequencies.

If you are prepared to accept a moderate VSWR on the feedline and to "fine-tune" with an ATU, the particular trap values are probably less critical.

73,
Steve G3TXQ

[pjm0bhn]

Originally posted by steveeh131047
Perhaps I should have explained :)

You can build a trap dipole that works on 40m and 80m with a wide variety of LC combinations for the trap; they just need to be parallel resonant at 40m, and then you can adjust the length of wire outside the trap to get the 80m resonance.

But, for the antenna to then also be resonant on 20m, 15m and 10m requires particular wire lengths in combination with particular values of L and C in the trap.

For example a 40m trap comprising a 22pF capacitor and a 23uH inductor would be fine for a 40m/80m dipole, but it wouldn't give you the other 3 bands.

The ARRL Antenna Book shows a design using coax traps which has 32.3ft inside the trap, and 21ft outside the trap. The traps are 8.75 turns of RG-59 close wound on a 2.375" former and are tuned with a dip meter for resonance at 7150KHz. They also show a "dangling" 6ft length of wire positioned 4.9ft outside the trap which permit a bit more flexibility in adjusting the resonant frequencies.

If you are prepared to accept a moderate VSWR on the feedline and to "fine-tune" with an ATU, the particular trap values are probably less critical.

73,
Steve G3TXQ O.K Steve all noted,at the moment i am only interested in 80 & 40 mtrs,will the trap i made be sufficient for my needs?.If and when the propogation improves then i might try the traps you mentioned in the arrl antenna book to improve the antenna.

73,

[steveeh131047]

Originally posted by pjm0bhn
O.K Steve all noted,at the moment i am only interested in 80 & 40 mtrs,will the trap i made be sufficient for my needs?
73,

Paul,

The 80m/40m dual band option is a much easier requirement - it simply needs the trap to be resonant at 7050 KHz.

Do you have some way of checking the trap resonant frequency, such as a GDO ?

Steve G3TXQ

[coffindodger]

paul if not send it me ill tune it for that and send it you back.. got a 259 here its worth its weight in gold..

billy

[pjm0bhn]

Originally posted by steveeh131047
Paul,

The 80m/40m dual band option is a much easier requirement - it simply needs the trap to be resonant at 7050 KHz.

Do you have some way of checking the trap resonant frequency, such as a GDO ?

Steve G3TXQ No Steve i don't have one,I used a coaxial trap design program,followed the measurements wound coax on former.

paul..

[pjm0bhn]

Originally posted by coffindodger
paul if not send it me ill tune it for that and send it you back.. got a 259 here its worth its weight in gold..

billy I may have messed up billy,if resonance not correct it would be dificult to open because i secured windings & weather sealed it "Numpty"....although i followed trap design program to the letter.

paul..

[steveeh131047]

Paul,

Having got as far as you have, it might be worth just giving it a try. You have some leeway by adjusting the inner and outer wire lengths.

But for the future it's a good idea to have some way of adjusting these traps; even following a design to the letter there can be variations in the resonant frequency.

If adjusting the wire lengths doesn't get a reasonable VSWR, I'd suggest you take Billy up on his kind offer.

Steve G3TXQ

[coffindodger]

Originally posted by pjm0bhn
I may have messed up billy,if resonance not correct it would be dificult to open because i secured windings & weather sealed it "Numpty"....although i followed trap design program to the letter.

paul..

i used this from the web

http://degood.org/coaxtrap/


i found the measurements given here were a good starting point only.. on my first attemp i made one as exact to the design as i could but it was out so ended up using the figures as a guide only.. which happened to be quite good as a guide

i made mine all on the same size formers but having the 259 it wasnt a problem to tune them..

you will find weatherproofing them will change things also even to a point it may be well off..

when i made mine i had enough room between turns to allow for any adjustment...

i doubt even if you followed the design to the letter it will be tuned for where it says it should be..

billy

[pjm0bhn]

Originally posted by coffindodger
i used this from the web

http://degood.org/coaxtrap/


i found the measurements given here were a good starting point only.. on my first attemp i made one as exact to the design as i could but it was out so ended up using the figures as a guide only.. which happened to be quite good as a guide

i made mine all on the same size formers but having the 259 it wasnt a problem to tune them..

you will find weatherproofing them will change things also even to a point it may be well off..

when i made mine i had enough room between turns to allow for any adjustment...

i doubt even if you followed the design to the letter it will be tuned for where it says it should be..

billy Thanks Billy & Steve you have both been very helpful,i will give the trap a try see how it goes.Should be getting a mfj-974b tuner this weekend so this will help.

73s
Paul.

[coffindodger]

no problem, like i say if you want you can send me the trap and ill tune it for you ,take any guess work out of it..

i gave mine away or you could of had one of them ,i only saved the 10m ones just to go with my homebrew collection ..

billy

like steve says give it a whirl there still may be a high enough impedence at 40 to cut the rest of the antenna off ..

billy

[M3WHN]

You could try this one. I got the measurements from the RSGB today and it looks like a good one to make.

All you need is about 40m of wire, a 1:1 balun, isolators and some PVC tubing. With it being 41 feet (12.5m) long it will fit into a small(ish) garden.

The antenna diagram is from the RAOTA book.

[pjm0bhn]

Originally posted by M3WHN
You could try this one. I got the measurements from the RSGB today and it looks like a good one to make.

All you need is about 40m of wire, a 1:1 balun, isolators and some PVC tubing. With it being 41 feet (12.5m) long it will fit into a small(ish) garden.

The antenna diagram is from the RAOTA book. looks like a interesting project,i have all the bits may try this when weather picks up.I tried the so called unun in my opinion it is very poor,to much loss poor on recieve & noisy,i tried a 63ft length of coax tuned against ground and it performed better.

Paul

[M3WHN]

Well you could try a 1:1 balun as described here in the link:

http://www.hamuniverse.com/balun.html

Seems reasonable and very much low tech in approach.

[steveeh131047]

Originally posted by M3WHN
Well you could try a 1:1 balun as described here in the link:

http://www.hamuniverse.com/balun.html

Seems reasonable and very much low tech in approach.

That reference makes misleading claims for the bandwidth of an air-cored balun. It is impossible to achieve good choking impedance (say > 500 ohms) with an air-cored balun across the range 1.8 MHz to 30 MHz. About the best you can achieve is a 4:1 ratio in frequency e.g 7MHz to 28 MHz.

The problem is that when you have enough turns for it to work on 160m, you are way above its self-resonant frequency at 30 MHz and the choking impedance is therefore low.

But it's an effective solution if you only want to cover some bands, provided you construct it with those bands in mind.

Steve G3TXQ

[M3WHN]

So is there a balun that can be made which will work all and be a air cored balun?

[steveeh131047]

In a word, "No".

As I mentioned, you can achieve about a 4:1 frequency ratio at best. So you could do 7-28 MHz or 1.8-7.2 MHz; but you cannot do 1.8-30MHz. To cover that range you need a ferrite core of some sort.

Take a look at the choking impedance measurements made by K1TTT on air-core baluns, remembering that a magnitude of 500 ohms would be considered an absolute minimum:

http://www.k1ttt.net/technote/airbalun.html

You can see that none of the designs gets close to covering 160m thru 10m. Even the ferrite bead design - the rightmost column in the table - doesn't quite meet the criterion, although it does better than any of the air cored options.

Steve G3TXQ

[pjm0bhn]

Hi,well i tried the antenna & it seems to work ok,all but 40mtrs.

SWR on 80 is very good,resonant on 3.600 1:1 swr, 20mtrs 1:5,15 mtrs reasonable well within tuner limits,as is 17 12 & 10mtrs.

40 mtrs,it will tune with tuner but can't seem to get swr anywhere near a reasonable level.It may be that there are two large heavy steel gates close to the 40mtr section of antenna,or it may be the 20ft steel support pole causing rf coupling,although the vertical section is stood some 6ft away from pole & the gates.I have good ground continuity & ground post is heavy duty aluminium pole 2.5 ins o.d, driven 5ft into ground,ground consists of 3ft of top soil & under this 3ft of clay.

Any idea's anyone.

cheers
paul.

[steveeh131047]

Paul,

Can you remind us what your current set-up is. There have been so many different suggestions in earlier postings I can't remember what you ended up building .... it's an "old age" thing :)

Steve G3TXQ

[pjm0bhn]

Hi Steve,if you can remembr i decided on the inverted L as suggested by yourself.

I made 40mtr coaxil trap,at the time i had no means of tuning it i.e with dip meter,i have now purchased a grid dip meter with various coils,just waiting for delivery.My layout for the antenna is same as before except i have not fed the pole has suggested,instead i used standoff cords which bring the vertical part of antenna about 6ft away from the pole.

Cheers
paul
m0bhn.

[steveeh131047]

Paul,

Thanks for the reminder. If 40m is causing problems I guess the obvious things to check are:

1) The trap resonance, once you get the GDO

2) The length of the 40m section between the feedpoint and the trap.

If you measure the VSWR at either end of 40m without any tuner in place, does it look significantly lower one end of the band compared to the other? That might give a clue as to where the resonant frequency lies.

I'll try modelling the effect of the adjacent pole; is it earthed or isolated from ground?

Steve G3TXQ

[pjm0bhn]

Originally posted by steveeh131047
Paul,

Thanks for the reminder. If 40m is causing problems I guess the obvious things to check are:

1) The trap resonance, once you get the GDO

2) The length of the 40m section between the feedpoint and the trap.

If you measure the VSWR at either end of 40m without any tuner in place, does it look significantly lower one end of the band compared to the other? That might give a clue as to where the resonant frequency lies.

I'll try modelling the effect of the adjacent pole; is it earthed or isolated from ground?

Steve G3TXQ Steve the swr on 40 is very high from bottom to top and does not vary,i think swr is about a 4.0 all through the band.The pole is isolated from ground mounted to a 6ft brick wall.Verticl 40 mtr section 33ft from feed point to trap and 28ft from trap to end insulator.

paul.

[steveeh131047]

Paul,

I just did a bit more modelling of your system, including the presence of the mast. Best results for 40m/80m VSWRs were with 36ft of wire from the feedpoint to the trap (26ft vertical + 10ft horizontal); then 24ft outside the trap.

When I introduced the nearby mast it had negligible effect if the mast was isolated from ground. With the mast grounded there was some small effect on the resonant frequency, but not enough to worry about.

The correct tuning sequence is:
1) Check the trap with the GDO for resonance at 7.05 MHz
2) Trim the inner wire length for minimum VSWR at 7.05 MHz
3) Trim the outer wire length for minimum VSWR on 3.65 MHz

73,
Steve G3TXQ

[pjm0bhn]

Many thanks Steve,as soon as gdo arrives i will do as you have suggested,I think it may be the trap resonance causing the problem.

Cheers
Paul.