Loop antenna resonance measurement with the MFJ-259B

[stefanmiller1953]

Very good job my friend.

[tonytonytee]

very cool.. for those that gave a negative for this video you should have your asses beat. this is a great video. all of the negative comments you are all little momms boy bitches..... thanks..... tony t..n0amy...

[sonick808]

great vid, thanks

[HarryHydro]

Have you had a trouble with flashover on that cap, or overhaeting toroid on TX?

[LB3HC]

@HarryHydro This is a receiving only antenna. It will not be possible to transmit on a loop antenna in this configuration. If you want to transmit you will have to do several things: 1) Use very thick copper pipe or several copper pipes connected together with e.g. solder or copper bands. This will reduce the Q of the resonant circuit. 2) You will still have very high voltages present over the capacitor, so you will have to use a vacuum capacitor or a capacitor with a large spacing.

[mikewm9v]

thanks for filling in where MFJ left off . MFJ needs to provide better video based

instructional content for their analyzer. They will eventually improve the display on this analyzer to include graphing . The loop is obviously far too short for anything other than half of a VHF eggbeater .

[Benelatus99]

Hej Marius! Your vdeo is very informative, but inconclusive, for example obviously you found a resonance, but was that resonant frequency any use for transmitting? Having worked in broadcast transmission for most of my life I'm content, for the minute just to listen, though perhaps one day transmit myself at low power. As a result of this, and because I don't have very much space magnetic loops of this sort are of great interest to me, hence my response.

[LB3HC]

@Benelatus99

Hi. Sorry for not informing about the resonance QRG. It was in the area of 10 MHz. My point wasnt excactly to show the excact resonance frequency but merely how you can measure it with magnetic coupling and the MFJ instrument. By the way, transmitting on a loop like that is not possible. You will get way too much loss due. To transmit on a loop you need much larger dimensions on the copper to avoid loss as well as a high voltage vaccum capacitor for tuning + efficient coupling.

[kevm666]

im just unsure how to check for resonant frequency and not lowest swr

[kevm666]

im tryin to work out the mfj analyzer but struggling a little,in the manual it says tune to zero on the impediance meter. but the impediance meter goes to zero throu out the hf band but only 1 part does the swr drop to 1-1 is this the resonant frquency or just the lowest swr.

[LB3HC]

@kevm666 Hi it depends on what antenna or system you try to measure. You can have resonance but not a 1:1 SWR! Resonance means that the inductive component has the same magnitude as the capacitive component. E.g. 2+(+j100) + 2+(-j100) will give you 4 +(+j0) so they cancel. (if we think of the real part of the antenna is divided into two halves of the loop in series with the reactive elements). However if you try to match that to 50 ohms you will have a big SWR even if the antenna is resonant.

[aeonios]

Hi dr Marius!Ufb video. I have had success also in building my own mag loops for HF but can't solve the problem yet that the antenna system shows additional electrical component reception also if coaxial is longer than some meters. I experimented with such antennas because they seem to be immuned from QRN in the The antenna behaves ufb if it is close to the rig (i.e. portable operation).

73 de Sv1eex - Nik

[LB3HC]

@aeonios You dont have a balanced antenna then. Try with several ferrite beads (cores) on the coax.

[aeonios]

@LB3HC Hi thanx for the idea. Do you mean that I don't have a balanced line?Tried with ferrite beads but the problem remains. 73!

[LB3HC]

@aeonios What I meant is that if your antenna SYSTEM is in one way or the other unbalanced, it will easily pick up common mode noise. You cannot use any type of ferrite core or bead. The core you shall use will have to have a reasonable Q value at the frequency of operation. Also the inductance at the frequency of operation of the coax wrapped around the core will have to be approx 1K ohms or so to have any effect. Also the feed arrangement must be balanced, Try with a loop inside the loop.

[aeonios]

@LB3HC Tnx for your thoughts. I have the problem no matter if I use gamma match or internal loop. I have tested two different types of inside loops as far as the feeding in concerned but the problem remains with the possible electrical behaviour. I will test with a toroid as well the way you set it up in the video example above and I will post my findings.

[oskar01963]

Hello from Croatia

I am so familiar with bridge measurement instruments, today's technology give us microprocessors , and together this make useful instruments , no more complex reading from data chart to know what really happened, just attach antenna and read results.

Have a nice day

9A3HP Zoky

[kc7fys]

Dying to see the end. Excellent video.

Best 73,

Jonathan KC7FYS

[Aromaz2012]

Thanks Marius, just opened my mind for other possible uses of this routine.  Very interesting idea.

[LB3HC]

@Aromaz2012 Very good ! You can use it on other antennas and systems too!

[soroastronik]

Este MFJ es el sueño de todo radio aficionado... ¡ESPECTACULAR! de LU1WGO, 73

[LB3HC]

Hi Joe! Your 15 meter dipole may change resonance frequency in case it is close to metal objects. A dipole antenna also changes impedance at the feedpoint when it is close to the ground. Therefore it is recommended to elevate the antenna when measuring. If you want you could try to measure with the MFJ in the resonance mode and only look for the frequency when XL=XC and ignoring the resistive part of the termination (like I mention in the video).

73 de LB3HC

[mygroovylespaul]

Thats fantastic Marius!

Can you help me with my mfj259b ?

I want to make a resonant dipole for my qrp 15 meter dipole handheld.

I just recieved my antenna anylizer for Christmas.

My question is........... Do I have to elevate my antenna to check and adjust resonance? ... or can I do it in the house only a few feet off the ground?

Thank-you...Joe

[lustrup]

Kjempe bra video....informativt!

73 LA3EQ Jan

[LB3HC]

@lustrup Veldig bra ! MFJ instrumentet er OK, men det er ikke 100% nøyaktig på magnitude på de reaktive elementene. +/- 30 ohm kan sees ofte. Jeg driver med en veltor nettverksanalysator nå som vil gi bedre resultater, men den er ikke like portabel. 73

[teamfab]

Very interesting and educational

[mygroovylespaul]

I meant to write - Hello again FROM Canada.lol

[mygroovylespaul]

Hello again for Canada!

I just bought the very same mfj antenna analyzer as you have.

I am very interested in vhf/hf home built antennas. I recently built a 6 meter 6 element yagi and look forward to tuning it and getting on the air, soon.

I am currently studying for my basic licence.

I certainly will, check out your other videos

Good day.......... Joe

[LB3HC]

Hi Marek. Thank you for your comment ! Have a good summer. 73 de LB3HC

[mygroovylespaul]

cool!!!

[sp4ndq]

Marius, ur movie is interesing. VY73 de Marek SP4NDQ