About Capacitors ... Part 6 Coax Cable capacitor for Loop Antenna by Andy Davies.
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- เผยแพร่เมื่อ 26 ส.ค. 2024
- In this video I show you a high voltage capacitor made from coax cable. This capacitor is used to supplement the tuning capacitor on my 17 Metre (18MHz) Magnetic Loop antenna. With the additional 'Coax' capacitor I'm able to operate the loop on the 40 Meter band (7 MHz) I'm not saying this is a good antenna I'm simply showing the capacitor that I made and used for this application.
Kind Regards ... Andy gw0jxm
Please see the comments box for any updates additions or corrections.
Very well explained. I enjoyed the video very much.
This is great to see practical applications of what otherwise has proven to be incredibly elusive to my understanding. Thank you!
Thanks
... Andy
Until the diagram, I could not visualize how the coax would work hooked up to both sides like that. Thanks! I'm going to do mine the same way.
Well done with some good points - thanks. Trying to learn all I can before embarking on my own 40/20 and 160/80 mag loop antennas.
Thanks for shar your great idea 73 De VE7JAI
verry helpful! now i can remember this part of education, that i already forgott!
thx, 73 , dg2r?
@MrVinamp Hi there, no, the coax capacitor is only a capacitor it isn’t like a balun, a balun (balanced to unbalanced transformer, for those not familiar with the term)The balun acts more like a choke or 1:1 transformer so I guess a balun is more ‘lumped’ L than C. I was going to say in the video that you can’t make the capacitor out of one or two long pieces of coax as you start to get onto characteristic impedance issues where length is counterproductive due to the inductance. Regards Andy
I have been cleaning scratchy and crackly volume pots with WD40 for years. since 1982 (ish). that was always my first line of attack and I thought it was common knowledge and the normal way of repair as WD40 was much cheaper than dedicated switch cleaner that also had the same effect. Yes I also used WD40 as low voltage switch cleaner.
Very interesting Andy...I am not a Radio Ham operator but I am a qualified radio and TV engineer from the early 80's. (C&G 2240 to 2242)
Not really in to Ham Radio but was using CB radio since 1978... ;)
In the C&G guilds 2240 electronics course I feel like I was wasting my time. I already understood everything as I started learning from the early age of 7 (so my parents tell me) What a waste of time!!!!
Thanks Andy this was very interesting. Nice antenna by the way.
I like it
@banjax66 Hi there, well I guess you have to go through the exam procedure and be measured and assessed so you can get a job and if you’re employing someone a qualification, hopefully, is proof of some ability. Having said that some of the most creative engineers I’ve employed have probably been the least technically qualified. And I know I’m on dangerous ground here but some of dumbest things have been done by some of the more technically qualified. Kind Regards ... Andy
thanks for sharing !
Can you Please add a small bit of video to show us your station "On the Air"? Thanks!
Thank you great effort.
I was thinking on making one using lmr600. I know it's rated at 5.5kw watts at 30mhz and 22.81 kw at 1.8mhz of the ham bands. having a voltage rating around 4000 volts with capacitance around 23pf per foot. putting it, in series and parallel with remote switching, with a big variable cap to tune my loop. I'm building a big loop then using loads of capacitance to tune up in frequincy. if I'm wrong please correct me. I'm self educating and asking for steerage.
@banjax66 Hi there, well it’s not really a problem I’ve had, but you should understand that I don’t do a lot of repair work. For what it’s worth I’ve picked up a rely helpful tip from ‘AllAmericanFiveRadio’ on YT and that is that you can resurrect the most awfully scratchy carbon pots by giving it a sniff of WD-40, not too much mind you. The trick is to leave them to soak in a bit (hours) but it really does work. I’ve saved several very badly worn pots this way and I’m told it lasts. ... Andy
Hi Andy. This question has nothing to do with Caps..
It's to do with potentiometers actually...
My question is do you ever have problems getting the required pots?
I just wondered as the old style markings for:
Linear was A but became B or LIN.
Log was C but became A or Log (just to confuse things with linear!)
Antilog was F but they don't seem to exist anymore!
(Antilog was like a mirror image of Log from a resistance scale)
@banjax66
Continued:
The reason I ask is because I was repairing an amp and the volume pot was marked as C. (old code for log) I told the sales guy I need an A type.
As you can imagine he argued the toss with me and said A was linear...
I wanted a log!!! hehehe.
If you strung them all out in a line (with same exact connections, would it be more or less or same capacitance, just wondering if the close packing has an extra advantage ( i would think it would at least slightly different bc of interaction by close (or not close) proximity of the 8 coax sections to each other. I have found that with a TV coax, doing winds (coiling) the coax it can "tune" the antenna better (or worse) depending via apparently a capacitance appears across the coils of coax (nothing was disconnected at all, just coils of slack coax). Thanks for your advisement. In other words what picofarads would I need to tune my TV antenna.. THANKS !! Fyi: I do have a 10 m band ham set.
Hi as each of the coaxial capacitors outer screen, effectively screens its own inner core from the surrounding outer core. So none of the capacitors affect one another no matter how close they are.It suited me to have a close bunch of capacitors to keep it all tight, but yes they could be strung out in a line and so long as the interconnecting inductance is not a problem it'd be okAll the best . . . Andy
My question was primarily about the different kids of potentiometers and their type markings. ie, Type A, B, C and F. I ask this because of some old amplifiers I have just repaired and the pots had the old style markings on them. One was F. Try getting an F type pot these days!
THanks for posting Andy.. I was curious what power limitations have you experiences with the coax capacitor? I've tried RG58 skinny coax in the past, but recalled some issues once getting past the 50 watt mark.
Hi I couldn't be specific about a maximum rating for the coax capacitor but I've used it on 80 metres with a linear amp without any problems.
I wonder if you had current or voltage problems. i.e. flashover or meltdown?
All the best . . . Andy
@@AndyDaviesByTheSea I would definietely say flashover at around the 50 watts mark... It was only RG58 howver.. That may of been part of it..
also no wiper resistance
Are the plates used made of copper plated with silver plating ??? What is the normal used material for this type of capacitors ?? Thanks
Hi, theses are normally silver plates brass.
@visualco2
Hi there, I can’t identify your capacitor from the number but I’m sure if you ask the question on QRZ (I see you’re listed) you should find someone who can help you. As a guide, I’ve used 2 halves of a split stator air capacitor in series, each half has a ~0.050” air gaps so that is equal to a total of ~0.100” gap and put ~100 watts into it no problem. Have a look at some of the ‘Magnetic Loop’ web sites, google w2bri.
I hope that helps.
Kind Regards ... Andy
gw0jxm
Is this the same principle as a (coax) balun?
Nice loop. Do you know the 2:1 SWR bandwidth of the loop on 40m, say at 7.1 MHz? That might give an indication of how much loss your coaxial cable capacitor is adding (since we can compute the radiation resistance and the resistive losses of the 1.3m x 1.3m 22mm-diameter copper loop).
Hi, sorry I don’t have the 2:1 info to hand but I’d say it’s very very narrow.
Regards . . . Andy
GWØJXM