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Will this balun work ok? #antenna #40m

JohnL
 

i have this balun from an old end fed 1/2 wave antenna that I was using for listening.  I cut a new 70ft chunk of speaker wire for transmitting on 40m.  I don’t have an antenna tuner and I am just getting started with my first radio.  Does this balun look okay to use and it won’t harm the radio?  I doesn’t quite look like other 1:9 end fed 1/2 wave baluns that I have been reading about.  Here are some picts. 

Thanks 
johnl

Cor Beijersbergen
 

Hello John,

 

Your balun looks exactly like the ones sold on ebay now for listening. These are 1:9 with a core of unknown properties.

You have to make a decision, you could make a resonant halfwave endfed or a random length non resonant endfed.

 

Halfwave resonant:

Your wire length is almost correct, but the balun needs to be 1:49. You need a SWR meter to prune the wire to length, after that you don’t need a tuner and you may work other bands as well (20, 15 and 10).

 

Random length endfed:

The wire length is wrong, because it is almost resonant on 40 and with a random length piece of wire and a 1:9 balun it should not be. And you will need a tuner.

By choosing the correct length of wire you could work more bands also.

 

General:

The toroid in the balun is very small and the material is of unknown properties. I recognise the balun, it is being sold on ebay now as a very cheap balun for listening only. I don’t know what kind of transmitter you intend to use, what the power level is an what internal protection of the power stage it has but I would not risk my transmitter on this balun.

But it lends itself for improvement, a new toroid with a 1:49 winding of the right size (a 140-43 will not fit in the housing) may give you a decent balun for a halfwave endfed.

Google for “halfwave endfed” or “EFHW” and you will find lots of information.

 

Succes!

Cor – PA4Q

 

 

 

From: QRPLabs@groups.io <QRPLabs@groups.io> On Behalf Of JohnL
Sent: Friday, 2 August 2019 02:39
To: QRPLabs@groups.io
Subject: [QRPLabs] Will this balun work ok? #40m #antenna

 

i have this balun from an old end fed 1/2 wave antenna that I was using for listening.  I cut a new 70ft chunk of speaker wire for transmitting on 40m.  I don’t have an antenna tuner and I am just getting started with my first radio.  Does this balun look okay to use and it won’t harm the radio?  I doesn’t quite look like other 1:9 end fed 1/2 wave baluns that I have been reading about.  Here are some picts. 

Thanks 
johnl

Kārlis Goba
 

Cor, I agree with your detailed analysis. However, isn't a 140 size toroid an overkill for QRP levels?

--
Karlis YL3JG

Cor Beijersbergen
 

A 140 would certainly be an overkill for QRP, but John did not mention the power of his rig. He did not mention QRP. A 140 would make a 100 Watts possible, I use that myself.

 

Cor – PA4Q

 

From: QRPLabs@groups.io <QRPLabs@groups.io> On Behalf Of Karlis Goba
Sent: Friday, 2 August 2019 10:02
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] Will this balun work ok? #40m #antenna

 

Cor, I agree with your detailed analysis. However, isn't a 140 size toroid an overkill for QRP levels?

--
Karlis YL3JG

Russ@va3rr
 

A 140 toroid fits nicely in those inexpensive boxes commonly found on auction sites,,,

 

On Fri, Aug 2, 2019 at 10:39 AM, Cor Beijersbergen wrote:
He did not mention QRP
But it was posted to the QRP-labs group, not the QRO-Labs group ;-)

Joking aside, those little ferrite rings will do 5w with ease, and I've run them for hours in beacon mode with 15-20w
and no warming / losses.

Output stage was running into a dummy load for the test.

73 de Andy

ajparent1/KB1GMX
 

JohnL,

Short answer is no.

Longer answer is see AA5TB site http://www.aa5tb.com/index.html look at anything EFHWin the  index.

For a monoband radio a simple tuned coupler with a ~1:9 turns ratio should do the job well.


Allison

Kevin Zembower
 

Can you tell me what the name of those boxes is? What can I search for? What are the approximate dimensions?

Thanks so much.

-Kevin
KC3KZ

Bob Macklin <macklinbob@...>
 

Using an even number of 1/4W elements is a mistake. That raises the feedpoint impedance.
 
An odd number of 1/4W elements is a better solution. That way you feed the antenna with current.
 
For receiving any long length of wire will do and no matching should be necessary.
 
Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark" 

----- Original Message -----
Sent: Friday, August 02, 2019 9:31 AM
Subject: Re: [QRPLabs] Will this balun work ok? #40m #antenna

Can you tell me what the name of those boxes is? What can I search for? What are the approximate dimensions?

Thanks so much.

-Kevin
KC3KZ

JohnL
 

Thanks for the responses so far.  I am using my newly built 40m QCX.  Here is the link to what I purchased.  

Usmile LW1650 Portable Long Line... https://www.amazon.com/dp/B0141X3B5W?ref=ppx_pop_mob_ap_share

Noticed that one of the pictures has a SWR freq graph that doesn’t look good for 40m. 

 I am still learning CW (getting closer to being ready  for my first QSO) so I had been using the WSPR beacon to test transmission.  I was spotted one night only and I measured my RF output following the QCX manual and it was outputting 4-5 watts. 

So I am thinking something is wrong with the antenna or I don’t quite have WSPR configured right.  

johnl
KE0VPA


Russ@va3rr
 

KC3KZ de VA3RR

Kevin, the box is advertised on Ebay as measuring 2.56"L x 2.28"W x1.38"H. These are the outside dimensions. There seems to be a few boxes that would accommodate an FT140-43, plus connectors.

vy 73 de Russ

JohnL
 

I see a big price difference on T140-43 toroids.  Is there a certain recommended brand to get or are generic (I am assuming they are Chinese) ones okay ?

geoff M0ORE
 

Difficult to ascertain whose make they are as I have never seen any manufactures details on any cores.

make sure you are looking at the type mentioned, a FT prefix is a ferrite material and a T prefix is an iron powder material. Type 43 is a ferrite so if an advertiser is quoting for a T140-43, they are telling porkys. Ferrite cores are not usually colour coded but iron cores are.

On 02/08/2019 21:01, JohnL wrote:
I see a big price difference on T140-43 toroids.  Is there a certain recommended brand to get or are generic (I am assuming they are Chinese) ones okay ?

Russ@va3rr
 

JohnL. Buying Chinese toroidal is fraught with risk.

If your QTH is North America, buy from Diz at Kits and Parts. Or buy from any of the big part suppliers like Mouser or Arrow. Buy more than you need, as you can use these pieces for RFI suppression, too