Jim, your vacuum/blower is the perfect visual to explain "Q". I have been licensed four years. Was an Electronics Tech in the US Navy, in another life, early 80s. The principle is not foreign to me. When I watched the previous video on the "Rockland Rover" I was reminded of a conversation I had with a fella. He was buying an amplifier. I ask what radio, he said FT857D. What freq? 20M. The 857 is 100 watts HF, what are you experiencing I asked. Only getting out around 200 miles on a good day. Antenna? I asked. 20M Dipole. Then came the thousand dollar question, have you checked "Q". He told me it wasn't necessary, this wasn't a home made job he bought it from HRO. They take care of that, that's why he bought it. I tried to explain "Q", and the fact he was probably only radiating 10 maybe 15w the other 85w was more then likely heat. He just wouldn't hear it Me, Flabbergasted. Yes I am using your vacuum/blower analogy, best and easiest way I have ever seen to visualize the principle. Great video!
Jim, thank you for explaining what Q is and how to calculate it for those of us who did not understand it before seeing this video. Excellent work from our RU-vid Elmer, as always. vy 73 my friend.
Hi Jim! Excellent presentation! Love the fan as a prop. I switched from Ham Sticks to the ATAS-120A with the FT-891 in my truck. The ATAS-120A has a decent Q factor, but of course it isn’t going to compete with the bigger, fat-coil, antennas. On 40m, if I move much more than 10 to 15kHz, it needs to be retuned. I expected much more of a compromise in performance, versus my Ham Stick. The Ham Stick is (was) mounted top dead center of the roof of my truck. The ATAS-120A is mounted on the front left fender. The only performance weakness I’ve noted is in the direction of the front left of the vehicle. There is an approximate 2 S-unit difference on 40m. But to the left and right the two antennas are approximately equal. Out the rear, and especially the right rear, the ATAS-120A beats the Ham Stick by up to 2 S-units. I shot a 5-part series about the ATAS-120A. I ran both antennas for a while, with an antenna switch. I eventually removed the Ham Stick. Interestingly, I broke a pileup one night and worked Bill, ZS6CCY, while driving home from my daughter’s house. 100W into the ATAS-120A. Another night, also driving home from my daughter’s house, I worked a station in Ukraine and another in Bulgaria, back to back. I must admit that I didn’t expect so much from the ATAS-120A. 73, Jim de Doug, N4HNH
Thanks Jim. I received my Rocklin Rover in the mail this morning, and can’t wait to get it in the air! BTW, the mini size bag of M&Ms as a free gift is a nice touch! 😉
Great explanation! I'm an audio engineer so I was lucky to already understand Q from the audio side of things. I remember that contest, it was when I was first able to get on the air when I was licensed. I hear you so clearly here in Nova Scotia, I have heard your voice a couple times over the past couple weeks, the first time was a couple weeks ago, you were scolding someone for causing interference...
Yes Sir Jim. High Q is good for antennas but the concept of Q is a means to an end. If I want to use the fan to blow dust away I want a high Q , if I want to fan my face however I need the inefficiency to cover the broader area of my face. Lol
How low is too low and how high is too high? it depends. An antenna that has a very wide bandwidth is one that I would not buy. What do you think? 73, Jim
Great video, Jim! Just finished a 4 element yagi, tested with nano vna just now, and with a resonant freq of 147 MHz (SWR 1.02:1) the Q came out to 27.22. I'm pretty happy with that. This was my second antenna, the first was a measuring tape & PVC 3 element 2 m antenna. I still need to figure the Q on that one.
No more coils or traps for me. The c3 I made resulted in remarkable success over traps. I had the opportunity to op as W1aw during the contest. With a great group of guys. It was a lot of fun! 5 over 5 over 5 on 20m.
As I tried to comment before, this was a very informative video. I have not considered Q-factor before, but after reading more I now appreciate it. I get that Q is a ratio measure of the total power to the power lost. The given estimate using the band width has some very important limitations which I have just come across in measure the 40m performance of a Mad Dog 80 coil/17ft whip/ 8 5m ground radials. I was able to get a reasonable SWR of 1:1.59 at 7.200MHz(measured via nanoVNA). The Q obtained for the bandwidth below 1:2 SWR was 22.5. But this appears artificially too good because of the poor minimum SWR. For example, I could see a SWR of 1.9 having a Q-factor of 50 to 100. This of course would be garbage. Thanks for making me think! K0OKE
Good seeing you working the contest stations… it reminded me of the time I was fortunate (and grateful) to be able to speak with my favourite RU-vid Elmer on VK’s ANZA Net about 18 months ago. Thanks, Jim and best wishes! Peter, VK3ACZ.
This was a great video, Jim - clear and practical! The only instance where I diverge from this philosophy is with my 2m j-pole, where I deliberately built it a bit larger than normal, to keep the SWR low, across the band, given that my HT doesn’t have a tuner. I hope you’re doing well and I appreciate your well thought-out videos. 73, Tim VE1XR
Understanding things like this saves me from becoming a shop-aholic running around and chasing things that I truly don't understand, only to find that I didn't reach that new success I thought that a piece of gear was going to give me, because the people reviewing it weren't really teaching me the real science and the real math behind the gear.
I understand the points you are making here and appreciate the time you took to put this video together. However, I’d like to respectfully offer a counterpoint. A High Q antenna may not always be the best choice for a given situation. For example: If one is attempting to operate portable, an antenna that is easily packable and deployable may be a higher priority requirement than one that is electrically efficient. Even though the hypothetical Rocklin Rover may not be an efficient antenna like your tri-band Yagi, it’s a better choice for someone who needs a portable antenna and will work well enough to suit the needs of a casual, portable operator.
Good point and well written. I would counter with when portable and low power, I would think that you would want the most efficient antenna with a reasonable Q. I would think that getting the best ERP would be important. I understand that tuning and the environment make that difficult. What do you think? 73, Jim
@@ham-radio I agree with you to a degree but as I alluded to above, there is always going to be a tradeoff between efficiency and convenience in almost every antenna installation which may mean Q is not the most important factor even for low power operation. In other words, I might be willing to compromise electrical/RF performance for some other attribute that solves a problem for me a higher Q antenna can't in a given situation.
🤬🤬🤬🤬CONTESES 🤪🤪🤪🤪 Great exercise in number swapping. Hello Jim -- Great explanation and demonstration with your fan. My antenna must be a "minus Q" antenna - I run a T2FD which I find great, mind you its no Yagi. Having said that I have zero interest in contests but I do manage to work a bit of DX from time to time and receive a satisfactory report. I'm not bothered about signal reports, I'm happy enough if the other operator hears me. Its great to see you looking so well Jim, stay safe and take care.
Some low Q antennas for a given frequency can become high Q antenna systems when brought to resonance with a suitable transmatch if we are using a low loss transmission line like a good balanced line.
Jim, thank you for explaining the "q" factor. So my understanding now is the Delta loop would have a smaller "q" value than the half wave dipole because the loop has wider bandwidth. And the dipole is better for transmit strength. Correct? I use 14 gauge copper thnn/thwn 2. Will that give me a reasonable "q" factor of my dipole antenna?
I'm really enjoying this series. I have only been licensed for a few years and I was initially amazed by a lot of the "gimicky" marketing in ham radio. I too have noticed when something "new" comes out all the most popular youtubers race to make the review. They are usually all the same. How many base loaded designs does the world need? Obviously endless varieties. Wasn't it like over 75 years ago that hams figured out that mid loading a shortened vertical is more efficient? 73, KF0BBU
Question Jim: With my little tapped vertical at say 10 metres, it's wide: Low Q. But when I change the tap to the 80 metre one, it gets a narrow tuning, so it calculates as a higher "Q." But I don't see how the performance is better at 80 metres, of course it's not. So maybe there is less CAPTURE then? 73 DE W8LV
Hello Mr. Jim, I am wondering how can i alter (improve) the Q of an end fed half wave antenna that has been cut to the electrical length of the desired operating frequency (18 awg solid copper wire, 49:1 T240-43 torroid). Is loading coil necessary for improving Q? Would switching to thicker gauge wire help?...Thanks I do not currently own a VNA, there are more than enough versions of nano vna out there. As some one who builds antennas, would you please share your thoughts on antenna analysers and vector network analysers? Thanks...73 Anoop
Is the Q of the vacuum better with the blower attachment removed? My takeaway? For a High Q antenna, the bandwidth should be < 300kHz and resonance as close to ctr Freq as possible?
By the way, I have an ATAS antenna. It’s high Q for sure. (Will measure later and get back to you. ) if the ground plane isn’t good, then the Q is very low on this antenna.
Look at the coil diameter and the wire size/spacing then tell me it is high Q. It just can't be. I did an autopsy on one many years ago and found it to be really awful on the inside. 73, Jim
@@ham-radio Ummmm. Q of an inductor depends on the resistance. It's large-diameter silver wire. Very low resistance. This should relate to Q of the antenna. Nevertheless, this weekend I'll do a test of the Q on various bands using your method and let you know what I find. In the mean time, know that I've reached Norfolk Island on 50 watts using this antenna! Look at my log book. Most of Europe including Greece. Parts of Latin America too. And as the song says "we've only just begun" ;-)
@@ham-radio By the way, see this video where he compares a large-coil diameter and thick wire Wolf River, to a pretty small diameter and also apparently small diameter wire Gabil antenna. In his test it seems like really similar performance. He did not do a Q test. That would have been interesting. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Rqj7D0xk7AY.html
All I can say perfect explanation and visual display. By the way I don't know if you spotted my horsing around on last video comment. Looking by December putting a cushcraft a4s in the air, your comment appreciated. KA6PSD Robert
It is. And, it is a very clever design that works great. The antenna is genius. I wonder what Q they report. That would be interesting to know. 73, Jim W6LG
Thanks for the video. I use a very high Q screwdriver antenna and love it. Have reached literally to the other side of the world. By the way, what does it mean five nine six or five nine zero six? I just don’t understand the “six” part.
@@ham-radio Sorry, I just don't understand this and when I type "signal report 59 06" into Google, Google doesn't know what this means either. Other than your video, I've not heard of this while I'm listening to the bands. Could you provide more info about the "06" or a link to more info?
I'm wondering: when you were working your contacts, several times you reported "5 9 06". I understand the "5 9" report, but what does the additional "06" mean?
Can someone please tell me who/what company Rockland Rover is specifically referring to? Here’s another video putting it down, so I’d like to avoid it, thank you.
I am the highly paid CEO of Rocklin Antennas and Dick Deceiver is the Sales Manager. Sally Shipper runs the warehouse which is located in the garage of our HOA and CC&R single family residence. 73, Jim
@@ham-radio very fine business; I enjoyed the humor and had a good laugh, also! I understood everything from the videos very well as I did indeed watch them fully. Maybe some didn't understand my original question and comment. I put it out there, in general, to all thinking that someone would know the specific company and/or product you were referring to and maybe wouldn't be so hesitant to mention it. I do understand you were speaking in general terms and it is good advice. But, it sure did seem like you had 1 company in mind more so than some others that would also fit the bill. I thought I missed something that all the RU-vidr salesmen were pushing recently. One company comes to mind because you said expensive along with the usual other things. Not sure if it is Chameleon? No one dare give them a less than outstanding review. At least one RU-vidr had to change his review after getting scolded by them. They even go into the comments section and attack the commenters that I saw a couple of times in the past. I could understand not wanting to mess with them. Or maybe you had something else in mind. -Cheers
When you have a regular quarterwave vertical for example, it will have a XL. The Xc will cancel that XL if it is truly a quarterwave vertical. If we want to shorten it, we will add a coil to the vertical to cancel the added Xc from shortening the vertical. So if our radiator is shortened, these things happen. 1. Radiation resistance lowers. 2. Ohmic losses lowers. 3. XL (inductive reactance) increases with the added coil. So when we take the formula Q=XL/R, the XL increases and the R lowers. These actions increase the Q and we can say we have a higher Q. The bandwidth lowers. The equation you use is valid for series tuned circuits. Q = f0 / (BW). But the bandwidth defined is to be 70.7% or about a 3.4:1 SWR. So your Q will be much lower than what you are claiming on your Yagi. I would guess less than 25.
What is the Q of the coils used to shorten the antenna. If you have two similiar antennas and each has coils to shorten the element. One has a high Q coil and the other has a lossy low Q coil, which is better? Which will have the greater bandwidth? If you use the Fc divided by the BW, which will result in the higher Q? In your example, I did not understand what the Q of the coil was going to be . Why is BW defined as 70.7%? Where does that come from? If I am considering buy one of two yagis and the BW of one is greater than the BW of the other, which is going to be more efficient? I would bet on the narrow BW. That for me makes sense. If one yagi has loading coils that are low Q, the BW would be greater. Regards, Jim
@@ham-radio First of all, an antenna Q will be calculated or measured by the entire antenna as a whole. The frequency divided by bandwidth method can be used as Jim did. However he used the 2:1 SWR points and it should be the 3.4-3.5 SWR points. But if you have 2 similar antennas, your concern will be with the coil. A lossy coil may not be that bad. If you are using #32 wire, it will be lossy and probably burn up at 100W. But a #18 as opposed to a #10 might not be noticeable. The Q is simply calculated by finding the XL divided by the R. You can get XL on the NanoVNA at the frequency you are wanting to operate. You can get the R by taking an ohmmeter, zeroing it out and finding the R.
@@ham-radio Lower Q antennas aren't as bad as Jim is saying. As seen in his example, his Yagi Q is actually much smaller than what he believes it is and much closer to that "dreaded Q of 5". Tis far better to not worry about your antenna Q if you don't have coils and if you do have coils, get a laser thermometer and measure the temperature rise with a key-down over a few minutes. The whole concept of ABC (Always Be Chokin') is to reduce SWR by lowering your system Q. It will electrically increase your R and lower your Q in the equation XL/R.
