Trying to make a 50ohm 7Mhz antenna

Thread Starter

Microbe

Joined Oct 7, 2021
6
Hello.
I have bought a ham radio kit. The instructions tell me to connect it to a 50ohm 7Mhz antenna. I've searched how to make one but there are only blurry schemes of antennas I can't understand.
I would appreciate if someone that knew about this topic explained to me how to make one and how to determine an antenna's frequency range.
Thank you.
 

bertus

Joined Apr 5, 2008
21,681
Hello,

Do you have a ham radio license?
You probably need one, when you want to operate the device.

As for the antenna, have a look at the internet archive and search for the ham antenna books.

Bertus
 

Thread Starter

Microbe

Joined Oct 7, 2021
6
Hello,

Do you have a ham radio license?
You probably need one, when you want to operate the device.

As for the antenna, have a look at the internet archive and search for the ham antenna books.

Bertus
No I don't have one. If you see the link, it is not a professional ham radio, and won't interfere. Thank you for your help, I hope I can find a solution there.
 

DickCappels

Joined Aug 21, 2008
7,984
Transceptor de Radio de onda corta CC 9-13,8 V s-pixie CW QRP 7.023Mhz + carcasa de acrílico DIY kit para Ham Radio Audio

If you only plan on receiving, no license is needed in most countries (don't know about all). In the United States you need a license to transmit, even QRP, in the 7.00 to 7.300 MHz band.

Edit: In Portugal (where I guess you are) 7.000 Mhz to 7.200 MHz is reserved for amateur radio as in the U.S. (confirmng Yaakov's remarks below).

You can start your search here: https://archive.org/details/folkscanomy_hamradio

I highly recommend the ARRL antenna handbook. Years ago, I would save my allowance for months so I could afford to buy some of these book, and now they are free? Thank you @bertus !

What shape antenna are you interested in?
Dipole?
Loaded Ground plane?
Inverted-V?
Loop?

Or better yet, how much room do you have (a quarter wavelength antenna for the 7 MHz band would be 10 meters)

If you download the antenna handbook it will help you decide what type of antenna you should try to buy or build.
 
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Yaakov

Joined Jan 27, 2019
3,755
No I don't have one. If you see the link, it is not a professional ham radio, and won't interfere. Thank you for your help, I hope I can find a solution there.
It is a 40m CW transceiver and you must be licensed to operate it. There is no such thing a a "professional" ham radio, Ham radio is a name for the Amateur Radio Service.

If you are not licensed it will be a violation of both national laws and international treaties to operate the transmitter. Getting licensed is not terribly hard
 

SamR

Joined Mar 19, 2019
3,612
In fact, that QRP (less than 5W transmit) "Pixie" radio is from a Ham Radio licensed operator's design. Copied by the chinese... With the proper antenna and good band conditions it can communicate transoceanic.
 

DickCappels

Joined Aug 21, 2008
7,984
Do I really need a license to transmit with this?
Yes.

Edit: Speaking as a past president of an ARRL affiliate and a long-time member of the Royal Order of the Wouffhong, ham radio operators will not talk with you and instead may set out to put you off the air for good using a cruel torture instrument by the same name.

1633630739087.png

https://www.onallbands.com/what-is-a-the-wouff-hong/

Brought to us by our founder:
1633630773139.png
 
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Thread Starter

Microbe

Joined Oct 7, 2021
6
In fact, that QRP (less than 5W transmit) "Pixie" radio is from a Ham Radio licensed operator's design. Copied by the chinese... With the proper antenna and good band conditions it can communicate transoceanic.
So I would transmit if I had the proper antenna? I'm saying that if I had a smaller antenna I would only transmit up to a certain distance? Is that right?
 

DickCappels

Joined Aug 21, 2008
7,984
There is no provision that I could find for Portugal for even very low power transmission in that band. Get the license. I have several friends who have done so and if I still lived in the United States I would have one too.
 

Thread Starter

Microbe

Joined Oct 7, 2021
6
Thank you all. I will continue searching how to make an antenna with the ARRL Antenna Book suggested by you.
Bye.
 

DickCappels

Joined Aug 21, 2008
7,984
You might want to look into the legality of using ISM (Industrial, Scientific, Medical) bands for unlicensed communications. There have been some really exciting activity around 13.56 MHz - like transalantic communications on 10 to 15 milliwatts. Amazing stuff.
 

nsaspook

Joined Aug 27, 2009
8,906
You might want to look into the legality of using ISM (Industrial, Scientific, Medical) bands for unlicensed communications. There have been some really exciting activity around 13.56 MHz - like transalantic communications on 10 to 15 milliwatts. Amazing stuff.
We use a lot of 13.56MHz RF power, so some communication locations might have a lot of QRM near industrial facilities.

30,000 watts of 13.56MHz RF into a series of cavities like this for beam acceleration.
 
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SamR

Joined Mar 19, 2019
3,612
Biggest problem with 40&80M DX (long distance/transoceanic) communications is atmospheric noise. In particular summertime lightning. Band can be quiet and wide open on cold clear days in the wintertime and in the summer, you can nearly go deaf from the lightning static crashes. Don't remeber any industrial QRM but it would simply be a noisy spot on the band to avoid.
 

Papabravo

Joined Feb 24, 2006
17,296
You can match a 40M half-wave dipole antenna to 50Ω feedline by adjusting the the length of the legs. This assumes you have an instrument to measure the return loss like a nanoVNA. I do have an amateur radio license, and I've done it a few times.
 

SamR

Joined Mar 19, 2019
3,612
Used to build dipoles w/ #12 thhn both solid and stranded. Back then we used a dip meter. There was a company (MFC Microwave Frequency Company) that made frequency traps for dipoles. Made some good multiband antennas using them both for personal use and for Field Day outings. They seem to have fallen out of favor for off-center fed multiband antennas w/o the traps. All you need is a couple of egg (or dogbone) insulators, a balun, dipmeter, 500' spool of thhn/thwn copper wire, 100' tape measure, and a couple of buddies to help tune it and you could do one in an afternoon. To go multiband, you added the band traps which came with instructions for the rough lengths at which to place them in the dipole. That and a bit of fine tuning with the dip meter and you had a very serviceable dipole. In a pinch you could do it with a good SWR meter but not as accurately. Now, the nanoVNA is far more accurate. Didn't need to be #12 but that seemed like a good choice to lessen stretching. Made one from copper plated steel wire but all it took was one small nick and they would eventually rust and break on ya so after that always used copper wire from the local electrical supply house. Been a long time since I used the 80M band.

IMG_0835[1].JPG
 
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