Episode 571b Calculate, measure, trim dipole antennas Be a Patron: / imsaiguy
Пікірлер: 68
@bvds20073 жыл бұрын
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.
@metalfabman54772 жыл бұрын
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
@OC352 жыл бұрын
It seems strange measuring antenna lengths in feet as wavelength is always referred to in metres.
@IMSAIGuy2 жыл бұрын
America does not discriminate units. We love to use them all
@alklapaxida850 Жыл бұрын
these are must have devices , extremely usefull
@JxH Жыл бұрын
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).
@mjrtude4 жыл бұрын
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!
@IMSAIGuy4 жыл бұрын
Millions of Hams have used DIY dipoles without baluns and worked the world!
@mjrtude4 жыл бұрын
@@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
@IMSAIGuy4 жыл бұрын
@@mjrtude I just posted a video on 1/4 wave vertical and one in the future will be a discone
@lukas_06_photo83 Жыл бұрын
The matric one is SpeedOfLight/FrequenzyInHz*2 for the half wave in meters
@debohannan431510 ай бұрын
Isn't that speed of light minus the velocity of propagation of a conductor ?
@spy8464BB3 жыл бұрын
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.
@samuellourenco10502 жыл бұрын
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.
@binder0982 жыл бұрын
Well done.
@martinda74464 жыл бұрын
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.
@IMSAIGuy4 жыл бұрын
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
@martinda74464 жыл бұрын
@@IMSAIGuy What I meant was it's hardly worth deviating.
@IMSAIGuy4 жыл бұрын
@@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.
@martinda74464 жыл бұрын
@@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.
@debohannan431510 ай бұрын
There's a VP to consider also which is why the formula of 468/frequency is different from speed of light
@rapsod19114 жыл бұрын
nanoVNA output is not balanced, so I think that without balun you can't measure dipoles, right?
all radios are unbalanced. dipoles work just fine.
@skaramicke3 жыл бұрын
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.
@robertlundstrom80613 жыл бұрын
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?
@IMSAIGuy3 жыл бұрын
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
@frankbaron1608 Жыл бұрын
don't forget to account for the length of your patch lead
@chrishulbert4091 Жыл бұрын
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?
@debohannan431510 ай бұрын
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 Жыл бұрын
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?
@richardchambers2567 ай бұрын
That's exactly what I'd like to know.
@Tchipo100 Жыл бұрын
Always practical and interesting ! Mny TNX de ON4SG !
@stanleyj.mitchell4851 Жыл бұрын
For our metrics folks, 142 divided by the frequency.
@Lugeix Жыл бұрын
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.
@@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 Жыл бұрын
various lengths can be made to have a reasonable VSWR but will have different radiation lobes. no way to tell from a VNA measurement..
@frankbaron1608 Жыл бұрын
for metric it's 300/f full wave
@clems6989 Жыл бұрын
Remember 1234 1 side is 234 [234/freq mhz = feet (one side)] thanks to jim W6LG
@azarellediaz48929 ай бұрын
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?
@IMSAIGuy9 ай бұрын
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.
@k19radio134 жыл бұрын
Hi you're awesome. Do you ever try formula 142.5/frq. With pole ground few % longer...
@ltlt61179 ай бұрын
How a balanced antenna like dipole can be measure by an unbalanced device like nanovna???
@IMSAIGuy9 ай бұрын
this might help: kzbin.info/www/bejne/a6aoq2SBoK1-l9Usi=6QNml1qPb3UMakcr
@aerozg2 жыл бұрын
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.
Would the nano give any indication at all if one side of the dipole was shorter than the other ?
@IMSAIGuy3 жыл бұрын
yes, it would not be resonant. the SWR will go up
@RC-Heli8353 жыл бұрын
@@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.
@frankbaron1608 Жыл бұрын
150/f will give you half wave metric
@edisukriansyah52309 ай бұрын
Please make tutorial how to measure gain antenna using nano vna?
@IMSAIGuy9 ай бұрын
you can not measure gain with a VNA. kzbin.info/www/bejne/fJbco4Rvrt6Zitksi=ju_J4Fg20RQjVwDE kzbin.info/www/bejne/fIOyhKOrnNmAbqMsi=GY2TnC5ANBEvfAKr
@martinda74464 жыл бұрын
Plus remember that calculation double it for full wave.
@imperiallandwalkeratat Жыл бұрын
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
@qwaqwa19604 жыл бұрын
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.
@IMSAIGuy4 жыл бұрын
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/
@qwaqwa19604 жыл бұрын
@@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)
@IMSAIGuy4 жыл бұрын
@@qwaqwa1960 ok, how about an SWR meter?
@IMSAIGuy4 жыл бұрын
ok, how about a network analyzer with a return loss bridge
@IMSAIGuy4 жыл бұрын
how about the MFJ antenna analyzer? is that OK to connect to a dipole?