does SWL antenna have to be horizontal

[nay27uk]

I had a bright idea last nigh but not sure if it would work as I am not sure if SWL antennas need to be horizontal, the idea I had for an makeshift antenna would meen it would go strait up in the sky.

you may laugh but it had the idea of getting a 100M or more roll of wire placing it on some sort of easy reel system and conecting the free end to some helium filled ballons then just letting them go out the window untill the roll of wire is fully out,

[crusty]

Verticals work fine, but once any antenna goes over one wavelength long at the operating frequency it starts to become end-fire. 100m would be great for listening around 0-3 MHz but at higher frequencies it wont receive low angle signals as well. 25m would be a better choice for general coverage unless you do he bulk of your listening below 3 MHz. You'll also need to operate it against a decent ground or noise levels will be high.

[nay27uk]

thanks crsty I did serch on the internet for a calculator that I could enter my radios top and bottom frequencys into that would calculate the best length of wire, unfortunatly there is no sutch calculator.

The frequencys on my radio starting at LW through SW starts at 146KHZ and goes right through to 30.459MHZ I mostly listen from the 3MHZ ham bands through to 8MHZ as they seem to have the most activity both day and night.

but would like the exact length of wire that will work best right through my radios frequency range

[crusty]

Alas no one antenna works equally across such a wide frequency range. Try buying or make an UNUN (often called a longwire balun/magnetic balun/9:1 balun), hammer an earth rod in the ground and experiment with wire lengths for best results. Radials aren't necessary but a selection of random lengths won't hurt.

[nay27uk]

ok cheers for the info

[JOHN,YORK]

Have you worked out the cost of the balloons,not cheap.It would be brilliant if you could do it,that poor broomstick would be a bit lonely.If you do use a 9:1 as suggested by Crusty,here are some figures that I saw on a web site advertising a 9:1.

9ft......(7-29)mhz
23ft....(3.5-29)mhz
65ft....(3.5-29)mhz
94ft....(1.8-18)mhz
124ft..(1.8-18)mhz

There are no errors,as you will notice some of the figures are duplicated,I just copied them from the site.The 23ft one seems to be a handy size and good coverage.

Some of the balloons that I have seen,have a silver foil coating,if it is metallic,I do not know.If it is and you do fly them at 100mts,there is a chance that they might be picked up on airfield radar up to 25 miles away.
If you have a lot of balloons together,your neighbours might think that you going to do around the world in 80 days.
Cannot you persuade the girlfriend to stand on top of the flats and fly a kite aerial for you.
I might see you in the next few days flying over York,dangling from your balloons.
All in good humour.
Good luck,I hope it works for you.

Regards,John.

[ashdown]

One important point to bear in mind (may be obvious but still worth stating) is not to fly a vertical antenna within range of any overhead power lines.

Mike.

[mm3oqr]

Won't there be a risk of electric shock from the wire? I wouldn't do this, not with 100m anyway.

[mikecharlie]

I found an excellent PDF for the constrtuction of a 9;1 balun.::
Ive upoladed it here:
http://www.mediafire.com/file/1vqc3yc1h ... 0balun.pdf

[crusty]

Not sure a powdered iron toroid would be my first choice for a transmitting broadband unun.

[JOHN,YORK]

Been trying to find this one for the last few days,very simple to make from an old ferrite rod.As it is only for receiving,it should be possible to make it from multi core intercom cable,each core is .5mm tcw.Also,there should be no need to use a 8 inch rod,a 5 inch one should do.

LONGWIRE ANTENNA BALUN PROJECT,LOW POWER


Mike Charlie
How is that broomstick.Would you recommend it.

Regards,John.

[crusty]

I've built 2 of those John and IMO ferrite rods work marginally better than the cores. Sadly decent length rods aren't cheap or easily scavenged any more.

[JOHN,YORK]

CRUSTY
Sometimes,a good source of supply of ferrite rods can be your local charity shop.People take in old radios that they do not want,if you are lucky,you might even get a radio with a air spaced capacitor in it.Have you priced a Jackson capacitor lately,not cheap.
I missed out the other day,the local Heart Foundation shop had a Ghetto blaster in,going price £3.95.For that,I would have got a ferrite rod,telescopic aerial,2 speakers,variable capacitor,mains transformer and various components.Try getting all that from Maplins for £3.95.who do a (5*3/8) rod with coils for £2.09.
I forgot one thing,I would have got a working radio if I had decided not to strip it down.When I went back later in the day,it had gone.
Jumble sales and car boot sales are another source of supply.
Going back to the ferrite rods,I can remember reading some years ago,about someone who was trying to make them out of old VHS tape.I cannot remember exactly what he was doing,or what the results were.It might have been many layers of tape on a PVC tube,or binding together several ferrite rods.I have often wondered what the results would be,if you were to make a MW loop and put several layers of ferrite tape under the windings.
I know that I have gone off topic here,but I thought that it might be of interest to other readers.

Regards,John.

[mikecharlie]

Well, I salvaged a toroid ferrite out of a component from an old CRT TV, and made my first 9;1 out of that........did OK at the time.
I replicated the same circuit on a ferrite rod anly 1/4 inch thick and 2 inches long ,and it outperforms the toroid one by a considerable degree.

I have got a few ferrite rods now, and have even made a spare 9;1 just in case....

Getting hold of variable caps for making little ATU circuits etc........ is getting harder.
But even those little polycon variable capacitors in chaeper AM radios work well, I use one for tuning in a ATU for HF.........

John..........

The broomstick............has been lying around unused..........since I put a better / longer longwire along the fence ....it has made an improvement on HF listening and it is now picking up less noise.

Had some good results on the lower freqiuencies.......ATC Gander has been pretty good at nights and I am definately getting frequently stronger signals on the Helicopters on 5680...........

The 100 foot of wire wound on the broomstick can be kept for good use elsewhere if need be........

[JOHN,YORK]

Mike Charlie.
Your last post was very interesting regarding the ferrite rods,the ones from the CRT,I think were called focusing rings.I have several rods ranging from the small slab ones to one that I think is about 8 inches *3/4*3/4 inches.I will have to measure that one again,I know that it is a monster.There also small ferrite rings to be found in earphones,as yet I have not found a use for them.
I do not know if you read one of my previous posts to NAY27.I was explaining to him that I used to rap a few turns of wire around a ferrite rod,one end of the coil went to the RX and the other end had about 12 foot of wire on it.I was a cheap way of getting better reception from MW to about 3 mhz,to tune the aerial,you just moved the rod in and out of the coil.
I do not know if you can remember a device called the DEWTRON WAVE TRAP.I made a similar device some years ago,but mine did not have a RF amp in it.Mine consisted of a plastic box,a ferrite rod with multi tapped coil and a variable cap.All you had to do,was lay the box on top of the RX,one end of the coil had about 12 foot of wire,the other end of the coil was earthed(C/H radiator).Tune the RX,then tune the aerial,omni directional of course,but a gain of 2-3 S points.Of course,this was only good for LW/MW.

Regards,John.

PS......What has happened to NAY27,not been on all week.Has not been heard of since he was going to experiment with the balloons.I hope he has not floated away with them.That 100ft of wire that you have got on your broomstick would come in handy for his balloons.