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Author Topic: Advice on choosing an antenna that won't make my transmitter go boom  (Read 6219 times)

Offline RadRoadrunner

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I have recently bought one of the LuLu transmitters from eBay that broadcasts with a 10W carrier, 40W peak. Would like to find a cheap, lightweight antenna that won't produce a high SWR reading when tuned. Any and all suggestions are appreciated.
« Last Edit: September 25, 2016, 2210 UTC by RadRoadrunner »
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Offline Josh

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #1 on: September 26, 2016, 1543 UTC »
A dipole cut to the operating freq and in the clear will be very hard to beat for efficiency, a vertical with ground plane may get you a lower angle of radiation, however.
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Offline Pigmeat

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #2 on: September 27, 2016, 0026 UTC »
Dipole cut to length set up flat-top or inverted V style. They work well and the heaviest part is the coax. As close to foolproof as you can get. Stay away from power lines and try to get it up at least a 1/4 wavelength or higher if you can. Good listening antennas, too.

Offline RadRoadrunner

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #3 on: September 27, 2016, 0226 UTC »
Are there any kits or plans for this? Also, maybe a center loaded dipole?

Dipole cut to length set up flat-top or inverted V style. They work well and the heaviest part is the coax. As close to foolproof as you can get. Stay away from power lines and try to get it up at least a 1/4 wavelength or higher if you can. Good listening antennas, too.
Please QSL At:  sansswl@gmail.com

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Offline Pigmeat

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #4 on: September 27, 2016, 2312 UTC »
Go to any general ham radio site or do a search on "dipole antennas". There's plenty of info and step by step instructions. Putting together a dipole is like chewing gum and walking, just about anyone can do it.

Offline Stretchyman

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #5 on: September 29, 2016, 0853 UTC »
468/f, gives a Half wave dipole in feet and inches, so 67'10".

Cut it in the middle and insert coax.

You MUST USE AN SWR METER to check.

The impedance of the antenna will change depending on it's height above ground.

So install (temporarily) at final height, check VSWR, adjust etc, OK.

VERY Easy!

Inverted V is probaly the best compromise (local and DX).

Low (less than 40') dipole is great for local via NVIS.

Best for DX is a dipole higher than 1/2 wave so 70' +

Better still a vertical with lots of radials or a few raised (tuned ones).

That's it!

Inv V is simplest so try that first, just look for ANY 40m antenna diagrams and make the antenna longer.

It's VERY handy to have a (HAM) radio that can TX on any band as you can see where the antenna is resonant.

So if it's got a low SWR on a lower frequency you know the antenna is too long etc, simple stuff?!!

The antenna is just a piece or wire, it's NOT magic!!

Let us know what you decide to do!

Str.





'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

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Offline Stretchyman

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'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Offline Pigmeat

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #7 on: October 04, 2016, 1427 UTC »
I once read an article by a guy into QRP on a very similar antenna he used for dxpeditions in the boonies with the exception being he fed with 300 ohm TV twinline and used a small tuner, Stretchy. It was tapped in roughly the same spots on the coil.

The only reason he used the TV twinline was he could fit it and the dipole legs easily inside the coil form for storage in his pack. He used it in a variety of ways, vertical dipole, sloper, upright "L" (one of my favorite dipole variants), inverted "L" along with the standard "V" and flat-top setups.

At that size you could build two, one without a feedline, and set them up as a beam to the area you wanted to broadcast at. I'm having a brain fart at the moment, what's the spacing between the elements on wire beams, a tenth of a wavelength?

Offline Stretchyman

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #8 on: October 04, 2016, 1541 UTC »
0.1 is about right but depends! can go as much as 0.2.

Did much piddling round with a 11m 4 el quad in the 80's.

That was fun!

SNORT!

 ;)
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Offline Mr.ArchVile

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #9 on: October 10, 2016, 1922 UTC »
I'm having trouble in finding an ideal SWR meter

Offline EliteData

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #10 on: October 10, 2016, 1957 UTC »
I'm having trouble in finding an ideal SWR meter
that really depends on how much you are willing to spend on one.

Offline RadRoadrunner

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #11 on: October 10, 2016, 2055 UTC »
Just dug up an old part, it's expensive, but would it do the job? It's for 40 meters, and has an impedance made for up to 200 watts.

http://www.mfjenterprises.com/Product.php?productid=mfj-1621
Please QSL At:  sansswl@gmail.com

Radios: Tecsun PL-600, Tecsun PL-380
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Offline Stretchyman

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #12 on: October 11, 2016, 0727 UTC »
That's a TUNER, NOT an SWR meter, which BTW are dirt cheap.

Forget any kind of antenna tuner, put up a proper antenna, 68' of wire cut in the middle and fed with coax.

Is it really that difficult!

Not sure what you mean by  'impedance made for up to 200 watts'

?

impedance is measured in Ohms, Power in Watts.

Anyway don't bother with some expensive tuner, put up a proper antenna.

PLEASE!

If you don't the signal will barely get outside your garden rather than the 1000 miles it was intended for!

This is the simplest but yet MOST IMPORTANT part of any transmitter system.

Maybe I should supply antenna with every system??

« Last Edit: October 11, 2016, 0734 UTC by Stretchyman »
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Offline Mr.ArchVile

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #13 on: October 11, 2016, 1728 UTC »
The problem I am now having is in terms of land space,

Now to make the dipole I want to make is 67 feet, I don't have have that space easily available in relation to where I will place the transmitter.

I know I can do this instead, but I want to make it clear. For a inverted V antenna is the total wing length half a wave length meaning two quater wave lengths?

Offline Pigmeat

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Re: Advice on choosing an antenna that won't make my transmitter go boom
« Reply #14 on: October 12, 2016, 0255 UTC »
Yep. The legs of the dipole in "V" don't have to be that far apart, 45-50 feet between the tie off points will get you in the ballpark for good performance if you get it up 35 feet at the center. It's dead simple.

You're looking at a foot over ten yards for each leg, it's not that much distance, flat or V shaped.