#571b

Episode 571b
Calculate, measure, trim dipole antennas
Be a Patron:
/ imsaiguy

[@bvds2007]

Your NanoVNA videos are the most useful to get started quickly. Great complement to the guy with the Swiss accent, who goes into a bit more theory. Thanks.

[@metalfabman5477]

This is so great can't wait to start using my new Nano, love making antennas, and your simple explanations are superb, just deep6 the negative comments from all the want to be anal experts, way more people are learning from your videos than aren't. Keep up the excellent videos

[@OC35]

It seems strange measuring antenna lengths in feet as wavelength is always referred to in metres.

[@IMSAIGuy]

America does not discriminate units. We love to use them all

[@binder098]

Well done.

[@alklapaxida850]

these are must have devices , extremely usefull

[@k19radio13]

Hi you're awesome. Do you ever try formula 142.5/frq. With pole ground few % longer...

[@robertlundstrom8061]

Imsa guy, a dipole is said to have an input impedance of 72 ohms. Does that vary depending on the distance between the two feed points?

[@IMSAIGuy]

the 72 ohms can be derived with mathematics on an ideal dipole. actual dipoles are close. I don't now how much effect spacing the feed points would make. a small fraction of the wavelength. wire diameter makes a difference too

[@chrishulbert4091]

You seem to be using your red coax (?Z =88ohms). Is this why the smith chart green circle off to the right rather than centred on the 50ohm centre. What would be effect be of using a 50 ohm coax? Does it matter if it was calibrated to load of 50ohms at the start?

[@debohannan4315]

What would happen if you added a choke at antenna input ? Wouldn't that get you a better reading ? And isn't there a common mode current on the shield as it is there's usually current radiating on the outside of tne coax all the way to the source .

[@acestudioscouk-Ace-G0ACE]

This is a good way to experiment and learn, thanks for making the video. I presume you are calibrating the VNA from the antenna end of the red cable?

[@richardchambers256]

That's exactly what I'd like to know.

[@azarellediaz4892]

That is how I learned decades ago to measure for a dipole but my doubt has always been, how do you account for the wire needed to tie the wire antenna to isolators or center balun?

[@IMSAIGuy]

use non-conducting rope, if you use wire then there will be some effect. not as much as you might think. every antenna system needs to be measured as used and tuned.

[@JxH]

0:35 The units of the 468 constant would actually be Feet * MHz (often confusingly written as "Feet-MHz", that's a dash not a minus). Dimensional Analysis processes units as if they're numbers; e.g. 'Feet-MHz' (constant) divided by MHz (the input) = answer (in feet).

[@aerozg]

So this nano VNA actually generates its own signal? You don't have to hook up a trx to provide it? I thought you had to hook up a radio and then transmit either voice or cw to be able to measure swr in real time.

[@IMSAIGuy]

yes: kzbin.info/www/bejne/mYaTZomMe9FjhJI kzbin.info/www/bejne/r3iuiHWmnLNrhrc

[@RC-Heli835]

Would the nano give any indication at all if one side of the dipole was shorter than the other ?

[@IMSAIGuy]

yes, it would not be resonant. the SWR will go up

[@RC-Heli835]

@@IMSAIGuy I was wondering if any of the more complicated readings would tell you whether the radiator was short or the radial was short. It would be interesting to see the readings while lengthening and shortening the radial. I was reading yesterday where a guy with ground plane antenna had 3 different radials bent at different angles and maybe different lengths too. He could get 3 different bands without an antenna tuner. There must be some sort of way to situate them correctly with the analyzer or maybe trial and error and checking SWR with each adjustment? I was kind of wondering if a dipole would do that with different length radials while leaving the radiator alone? Not that it really matters just curious.

[@lukas_06_photo83]

The matric one is SpeedOfLight/FrequenzyInHz*2 for the half wave in meters

[@debohannan4315]

Isn't that speed of light minus the velocity of propagation of a conductor ?

[@spy8464BB]

Thanks for the video. I looked at the comments and as usual there is always an expert that chimes in to argue. This makes all this confusing for people that are trying to learning. I'm going to duplicate your example so that I can continue to learn. Thanks again for a real world lesson.

[@samuellourenco1050]

You can always not read those comments if they are confusing to you. Having said that, it is natural that there is space for debate. That's a good thing.

[@Tchipo100]

Always practical and interesting ! Mny TNX de ON4SG !

[@martinda7446]

The fact it is almost easier to calculate the exact dims using the standard formula I would advise anyone to just remember the speed of light.

[@IMSAIGuy]

yes that gets you close. the 'standard' formula has a 97.5% factor in it to shorten the length a bit. due to the length/wire-diameter effect

[@martinda7446]

@@IMSAIGuy What I meant was it's hardly worth deviating.

[@IMSAIGuy]

@@martinda7446 no you are right. I always want people to understand the simple ideas and not have to memorize formulas. gives a much better understanding.

[@martinda7446]

@@IMSAIGuy I absolutely agree, but here the relationship with the speed of light, the wavelength and frequency is so fundamental and easy to understand anyway it is a wonderful thing - is what I was getting at. I didn't mean to sound critical.

[@debohannan4315]

There's a VP to consider also which is why the formula of 468/frequency is different from speed of light

[@rapsod1911]

nanoVNA output is not balanced, so I think that without balun you can't measure dipoles, right?

[@IMSAIGuy]

rsgb.org/main/get-started-in-amateur-radio/antennas/your-first-antenna-the-half-wave-dipole/

[@IMSAIGuy]

all radios are unbalanced. dipoles work just fine.

[@skaramicke]

The VNA should be calibrated at the antenna connection point, so that it can measure the antenna itself no matter if the output is balanced or not.

[@frankbaron1608]

don't forget to account for the length of your patch lead

[@edisukriansyah5230]

Please make tutorial how to measure gain antenna using nano vna?

[@IMSAIGuy]

you can not measure gain with a VNA. kzbin.info/www/bejne/fJbco4Rvrt6Zitksi=ju_J4Fg20RQjVwDE kzbin.info/www/bejne/fIOyhKOrnNmAbqMsi=GY2TnC5ANBEvfAKr

[@mjrtude]

God bless you for putting this out here. I'm not sure what happened to our hobby that the newbies think that there is some magic to making an antenna. Perhaps the license exam no longer asks for formula frequency for a 1/2 wave? dipole. Remember back in the day running between the shack where you had your borrowed swr meter and outside snipping the wire? Now it's easier than ever and hams are spending $100+ for a simple wire antenna. They're missing a lot of fun and self satisfaction!

[@IMSAIGuy]

Millions of Hams have used DIY dipoles without baluns and worked the world!

[@mjrtude]

@@IMSAIGuy Exactly, I still don't use a balun..most of my wire antennas are 1/2 squares now and I don't think it would perform w a balun. Perhaps an RF Choke

[@IMSAIGuy]

@@mjrtude I just posted a video on 1/4 wave vertical and one in the future will be a discone

[@Walter-Montalvo]

Very cool. I wonder what is the result if you were to wind the wire around a wood rod, making it a coiled wire

[@IMSAIGuy]

www.nonstopsystems.com/radio/frank_radio_antenna.htm

[@stanleyj.mitchell4851]

For our metrics folks, 142 divided by the frequency.

[@ltlt6117]

How a balanced antenna like dipole can be measure by an unbalanced device like nanovna???

[@IMSAIGuy]

this might help: kzbin.info/www/bejne/a6aoq2SBoK1-l9Usi=6QNml1qPb3UMakcr

[@frankbaron1608]

for metric it's 300/f full wave

[@clems6989]

Remember 1234 1 side is 234 [234/freq mhz = feet (one side)] thanks to jim W6LG

[@Lugeix]

Given: A black box with a perfect world inside. Given: A single element end-fed random wire on one connector on the black box, and a perfect ground on another connector. Given: a Nano VNA Question: What is the length of the end-fed random wire antenna? History: I use to do fire clearance at a cabin. It had a single wire phone line that connected all the cabins in the canyon. The other wire for the phone was connected to a copper ground rod planted in the stream bed. I wondered what the length of the wire to where it was broken. Also, what bands would it be a great antenna for. It did make a great 160-meter and 80-meter antenna. I didn't have a nano VNA back then.

[@IMSAIGuy]

www.ni4l.com/portable-end-fed-160-10-meters-dipole-antenna-1kw/

[@Lugeix]

Not an answer. Its like 1+1=1+1.

[@IMSAIGuy]

@@Lugeix I thought they told you the length they used. it is a bit subjective as you have a transformer and it is 'random'

[@IMSAIGuy]

various lengths can be made to have a reasonable VSWR but will have different radiation lobes. no way to tell from a VNA measurement..

[@imperiallandwalkeratat]

love your videos. I was wondering if I could request a video on how would you measure and create dual band antenna like to this one: kzbin.info/www/bejne/m4fZeX-Gis18nZo How do you separate the 2 bands(make the coil, length, etc). Thanks

[@frankbaron1608]

150/f will give you half wave metric

[@martinda7446]

Plus remember that calculation double it for full wave.

[@aduedc]

Your measurement is not correct, you need a Balun. SMA & NanoVNA are common mode and your dipole ant is differential.

[@qwaqwa1960]

I don't think that can be considered a dipole, given the single-ended drive. It's a monopole with a really bad ground plane. Inches & feet? U gotta be #^&(%^ me.

[@IMSAIGuy]

dipoles without baluns work just fine. All radios are single ended at the transmitter. rsgb.org/main/get-started-in-amateur-radio/antennas/your-first-antenna-the-half-wave-dipole/

[@qwaqwa1960]

@@IMSAIGuy "All radios are single ended at the transmitter." Irrelevant. I've never heard of a dipole being connected to a SE xmtr. "The dipole antenna, which is the basis for most antenna designs, is a balancedcomponent, with equal but opposite voltages and currents applied at its two terminals. The vertical antenna is a monopole antenna, not balanced with respect to ground. The ground (or any large conductive surface) plays the role of the second conductor of a dipole. Since monopole antennas rely on a conductive surface, they may be mounted with a ground plane to approximate the effect of being mounted on the Earth's surface." (W'paedia) "A dipole is what is termed a balanced antenna. In an ideal world a balun should be used with coaxial feeder (which is unbalanced) to make the transition between balanced and unbalanced systems. The use of a balun will prevent the coax radiating any power or picking up any noise. In many practical situations it is possible to operate the dipole satisfactorily without one, but there may be a slight increased risk of interference if one is not used. Simple baluns can be bought from antenna suppliers, or made." (from your link)

[@IMSAIGuy]

@@qwaqwa1960 ok, how about an SWR meter?

[@IMSAIGuy]

ok, how about a network analyzer with a return loss bridge

[@IMSAIGuy]

how about the MFJ antenna analyzer? is that OK to connect to a dipole?