Deciphering Decibels Tell All for Ham Radio (Ask Dave
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- Опубликовано: 30 янв 2018
- Decibels got you down? Are dBm and dBW giving you headaches? Is it confusing when sometimes an antenna gain is given in dBi and other times in dBd? Watch this tell-all to learn about decibels as used in ham radio!
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This presentation seems to be the beginning of breaking a block i have about these numbers. I think your explanation was very clear. However, it will take me many more viewings to get the information into my thick head. Thanks.
Simply brilliant! Hats off to you OM Dave! 73 de VU2RJV
Thanks Dave. Just came across your Tube stuff while searching for FT8 info. Your log/db video brought back memories. As a young Civil Engineer, my first job was surveying on Interstate highway construction in 1969. Not an electronic calculator in sight! In the office, we used the Marchant "coffee grinder" machines to multiply and divide. In the field, log-trig tables were my best friend. I think they were 10 or 12 place tables. I still have my Post log-trig slide rule. Thanks for the memories.
Tim, NG3I
Thanks for tackling technical topics and applying your communications/presentation skills to them for us. Pretty sure I did not get all of this on my first viewing, but pretty confident I will have a working understanding of the topic after another time through.
Hi Dave. I think this is my first comment on your channel, been watching since September 17. You've taken something that's been taken for granted since I did O level maths back in the early 80s and actually provided background and definition to enable me to fully understand why log and DB are used. Many thanks you deserve a sub for that. 73s from M6UAW.
This brought out fond memories of college Math, AND, my slide ruler. In fact, I had to go find it and look at the log scales once again. Thanks for the excellent review Dave, well done.
Thanks!
You explained logarithms better than my college professor back in the 1970's. I could barely grasp what it insinuated until I heard what you had to say. Thanks Dave.
Moe K2JDM
Dave. I work in marine electronics installations. I'm also a lifelong radio hobbyist. I like working with numbers. Your explanation of dB is THE BEST, hands down, I have studied.
@@davidjames1684 Im gonna review DC's video when I can fit it in to understand your opinion. I'll get back to you in the near future.
@@davidjames1684 Sorry, David, I haven't. I recently had to switch my email over Gmail and Gmail stuck your note away where I didn't catch up with it until today. I'm really not all that impressed with Gmail , to be honest. Regarding the review of Dave's presentation, I will review it again, in time. PS DJ: I just reviewed your complete note of two weeks ago. Never mind.
Lol. Just noticed a log on the desk. I think I know where this is going to wind up. ;) Still watching ...
By the way, for those who don't know, CRC is short for "Chemical Rubber Company", the publisher. (It also stands for Cyclical Rendundancy Check for computer nerds.)
I hadto find my asprins after this one
Dave, You are an artist. I would only have hoped you would have added a brief history of the decibel, i.e. the phone company, the MSC and of course Alexander Graham B-E-LL.
I agree, but I had to keep it simple somehow. I only talked about decibels, rather than Bels. Also, when talking about logarithms, I completely ignored natural logs.
David Casler, yet you mentioned Napier.
Dave, what a shocker! I am a fellow Bruin! Graduated in December 1968 with a BS in Business Admin/computer programming and got my commission in the USAF. Was sent to SAC HQ, OFFUTT AFB in Nebraska, but before I left, I was advised that I would need a copy of the CRC so I picked one up at the UCLA bookstore. Still have it.
Sure is weird knowing you and I were walking around the campus at the same time! Go Bruins!
71/72 de William, k6whp
dit dit
Dave thanks for this and perfect timing as I have my nose in my "Advanced" text book reading return losses for my (UK) Advanced exam on Saturday. Regards Hugh 2EOEHA
Good luck with your exam!
Oh, boy... CRC gives me memories. Didn't know it had logs in there. I had the 1989 version.
That is an outstanding lesson on the use of dB and I thank you for it. And the timing is great because just the other day I said to myself I need to go back and review the topic and try to make more sense of it. You've done me a great favor tonight, Dave, and I greatly appreciate it.
wonderful information. I am getting things in order to make a 21cm 1420 MHz radio telescope dish and thought reviewing decibels and VNA stuff would be helpful? 🤔 thanks a lot. 🥳
I finally got it with the formula writtien out so I can understand the math. But right at the crucial point in the explanation, BAM! Focking commercial!.
i like your station log lol
starting to understand thanks! G. B. 73
That's a great summary Dave! Thanks for the great videos. M0NOM
My brain melted 15 seconds in…
I think if I watch this video once a day for a year I will begin to get it.
It's rough
logging produce produce lot of decibels, that's for sure.
And now for Powers of 3, 6 and 9...
Actually, for me the really interesting number is e, the base of the naperian logarithms. E keeps popping up in engineering (and, I presume, science). It seems to be one of the fundamental constants of the universe.
Natural base log and quadratic equations are right up for me Dave...
I love them like Ebola and small pox....
I'm happy with 3,6,9 and dB thanks. My brain hurts. I know maths is fun and rules the universe but I can't think that much without my eyes exploding sentient black goo all over the table.
Dave, excellent video as usual. Back in the day, I remember the log and trig tables were in the back of the high school algebra books. Let us not forget Voltage dB gain though. For equal input and output impedances the formula would be Voltage dB gain = 20 x log(Vout/Vin). Then there is a similar formula for current gain. These are both related the formula given in the video.
I know im randomly asking but does any of you know a method to log back into an instagram account?
I somehow lost my account password. I love any assistance you can offer me.
@Maximo David instablaster ;)
@Vincent Moses Thanks for your reply. I found the site on google and I'm trying it out now.
Takes quite some time so I will get back to you later when my account password hopefully is recovered.
@Vincent Moses it did the trick and I actually got access to my account again. Im so happy:D
Thank you so much, you saved my ass :D
@Maximo David Happy to help xD
Fantastic explanation. Thanks!
Guess I'll dust off my CRC tables too.
A few months ago I started doing signal reports thusly, you are one Bell, if S9+10db. Two Bells for S9+20db :-) ect. Some don't know what that means but others get it. I bet they don't know what a Bell is and who came up with the Bell :-) Your next video :-)
Well done as usual. Thank you.
What do you use for audio recording when making videos. Also are you using some kind of software TelePrompTer?
Sennheiser wireless mic, also sometimes a Rode wireless mic. Tascam DR-05 recorder. Audacity for processing, usually just compression. I have a homemade teleprompter. I use Autocue QStart free software.
David Casler thanks Dave N1DCH
David Casler e
Dave i have a question. is there one ham radio i can buy to talk on that has all frequencies instead of buying several radios for different frequencies.?. 73s and thanks.
Yes. Each major manufacturer has one. For Yaesu it's the FT-991.
lol @ Log On Table
Could you do a video on EME or moonbounce? Thanks!
Yes, if I can find someone near here who does it. It's rather specialized.
Dave, Something I've wondered often. Why is power 10log and voltage is 10log ?
Power is 10 log. Voltage is 20 log. I'll have to dig through the math and maybe make a video.
I had 1 year of general math in high school. I still don't get it.
Log man…
When someone says an antenna has 6dB gain, are really saying it has 6 dBd gain or 6 dBi gain?
Either that or 6 dBd. It's got to be 6 dB better than something. If no reference is stated, you're probably safe with dBi.
At 8:54, receiver gets a signal that is -73 dBm from an antenna. How is this a "large" signal? Is it femtowatt or something?
-73 dBm is 50 microvolts across a 50 ohm load. That is S9 on a properly calibrated receiver, which is a nice, strong signal.
Is there a co-incidence David? We find it hard to believe there isn't, but wonder if anyone knows either way :)
It's 5.01e-8 milliwatts, according to one calculator. That's what I was getting at. Guess I just never thought a readable signal would be that minuscule power-wise. Five hundred-millionths of a milliwatt?
Indeed. I figured it out once. Take a very ordinary path loss from a transmitter putting out over a trillion dollars. You will receive less than a penny. That's the scope of path loss!
Ha! My CRC tables are 14th Edition...guess we date ourselves!! 73, John/N6VTS
:-)
Whats money and wood log doing on the table 😂
The money is his tip jar, found over at KE0OG.com . The log was there for the joke... He had a table of logs, and a log on his table.
His tip jar and a Log(arithm)
Makes sense now
Huh?
kk4yze from Panama City, Fl
Thanks this was clear explanation for a non-math person like me.
You lost me at 1:15 where 10 log (2)=10x 0.301029996=3dB. Where did that number come from? Did you have to look it up in your log book? and again at around 5:27 where 2x=3dB. If 1000x = 30dB and 10x=10dB, how does 2x=3dB? I don't see a pattern that I can follow or use. I don't routinely carry a book of log tables around with me, so how can I do such calculations 'on the fly'?
3x 3dB give you 10db, which 10x, so it's like you're multiplying 2x3 equals 9 which is close to 10
Even with this great explanation, I still can't stand the use of dB. I don't know why exactly... Just seems like it's over complicating the matter... For example, if I say: 'Hey, how's that new antenna?' and the response includes "it has 6 dB gain" or something similar, all I can think is "couldn't you say it has 4X gain...?"
The use of decibels is near universal in the radio field, so trying to go against the grain will prove frustrating.
I'm not trying to go against the grain. I just feel like, in this day and age, in some scenarios, it adds something that's not necessary.
I totally get what you're saying. 10wattts rf = 40w e r p. 100w = 400 e r p, and so fourth. Db does seem to be unesssary for this application.
honestly, for a "modern" radio, it is a disappointment. CPU controlled automatic Bias anyone?