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Macavity

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About Macavity

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  1. So what does that say about the both of us? Don't answer that! lol I had a broken connector on a budget coax, so I snipped that off, and attached the remaining good connector to a T-piece between the two inputs on the MicroVNA (As suggested). This is the LogMag S12 plot: Or indeed, as you suggest, the basis of a potential "filter"etc. etc. The actual length of the coax (measured) was 2.60 Metres.... "Open" at the far (cut) end... So an "electrical" quarter wave?!?! The first dip is at 19.15MHz. The cable is (probably) RG58, so the Velocity Factor is 66% etc. If you put the figures into the (lambda/4) Stub Formula: 75 / f(Mhz) ) * VF = Length (Metres) 75 / 19.15 * 0.66 = 2.58 Metres !!! i.e. pretty close to 2.60 allowing for unknown connector effects! So I can also measure Velocity Factors as well... P.S. No detailed comments. lol. But we have the same ideas re. Smith Charts! The coax is effectively a "(complex) impedence transformer" yadayada... But at ONE frequency! So the variable frequency results in the convoluted loop/circle seen in practice! Have Fun...
  2. lol. I always felt, as a solvent, isoproyl alcohol is a bit wimpish tho'! I sense they don't like to sell absolute alcohol (ethanol) hic?!? Stuff like Benezene is Carcogenic... Ether is Aneasthetic... BUT there is Acetone... Dunno if you can readily buy it, but it's a good solvent... More polar? Attracts different "muck" to Alcohol? Miscible with Water or Alcohol. The main ceveat: it dissolves most Organics... PLASTICs notably! For cleaning optics, Acetone is mentioned (+water and isoproanol): https://www.edmundoptics.com/knowledge-center/application-notes/optics/cleaning-optics/ Another thing to avoid is Acids OR Alkalis! Pretty sure your nice Aluminium mirror would rapidly disappear leaving a glass blank?
  3. There is a wealth of stuff on this... More perhaps on Art & History websites? Of course, you cannot avoid the mix of Science and Faith of those times... (I'm a "don't care"!). But you can't beat a good Medieval Manuscript, I say: http://blogs.getty.edu/iris/written-in-the-stars-astronomy-and-astrology-in-medieval-manuscripts/
  4. For the sake of (minority? lol) interest here's the SWR measurement of the D777 Aircraft Antenna, at feed point, with short SMA coax! I did this "for reference" before it was committed to the sky! Note the absence of the sine wave due to 15m coax feed. As to which is the more VALID measure of antenna performance, I veer towards direct one! But the "whole system" idea is a valid point? For fun, I show FAMED "Smith Cart" of the Coax Fed D777 Antenna: This does show characteristic (pretty!) "resonace loop"(SWR close to 1.0) amidst the general "coax-induced" circlings over a wider frequency range! The "direct" Smith chart near resonance is a "boring" short ARC near 1.0! I think I now have some sort of handle on all this! lol. It can be explained with a little Antenna Theory. I am but a late-comer to all this good stuff... But certainly the NanoVNA is a useful tool / expanded my knowledge! See e.g. http://www.antenna-theory.com/tutorial/smith/chart.php These days: That others understand the detail is good enough for me!
  5. Reflecting on your SWR plot... I quickly learned (in practice frankly!) that measuring SWRs, via a coax, superimposed a "sine wave" on everything! It's "obvious", I guess! Maybe that's what you did in this instance tho'? The TRUE reading of an antenna SWR is measured at the feed point of the BARE antenna. Well, that's my story (now) and I'm sticking to it. lol It's "well known" that a dipole radiates at a third harmonic? 40m -> 15m. Not sure about "quad" elements. Possibly at the second harmonic?!?! My "Aircraft Band" Antenna fed via 15m coax. Note the "sine waves": I suspect "via coax" SWRs are still useful. At least you know your antenna hasn't blown away in the WIND! lol
  6. Good Stuff! Referring to "misc. stuff": Shortwave *HF* (longwire) antennae. I sense a CHOKE on coax (tuned radials?) is the way to go? (Thanks Mike @wxsatuser!). I imagine such things (Chokes!) help *generally* when we move up to VHF / UHF? For SWL's (me!) I begin to wonder if we need care AT ALL about SWR on HF Bands. Would I be right thinking that it's only "signal to noise ratio" that really matters? A WELL TUNED antenna for VHF/UHF seems "good thing"? You can reject off-band "QRM" etc. (Remember Q-codes?)! I did find another really good use for my MicroVNA. You can measure velocity factor for COAX... Make Coax Antennae... Coax rejection filters? Get an SMA T-piece and use both connectors... Plot the "S12" (whatever) throughput etc. etc. Not *everything* "Rosy" here. lol. Amazon "seduced" me into buying cheap 30dB LNA! Soldered power leads... Dead as a Door Nail?!? No surprise? Next month, I will have the funds to buy a decent LNA (Low Noise Amp) that actually works?
  7. Are we talking Camping <Shudder> or making (laudable) Telescope Dewshields? Ah..." I want to make foam dewshields"! I made a number of the latter by accurately "squaring" the edges of matress foam using a Craft Knife. I then (approximately) aligned the latter into a "cylinder" using short pieces of (paper) masking tape. I didn't even TRY to stick the edge together! I then secured it all using the popular "Gorilla Tape" (whatever) *along* the join... The key (for me) was not to try to join the bloomin' stuff edge to edge! You can use the telescope of dew shield... a "random cylinder" as a template? Not always my virtue, but *patience* is/was a significant part of all this. lol.
  8. A sad loss... A life well lead? A CBE among the (many) OBEs.
  9. Heheh. Well it is a bit of a weird one! But in fact, listening to almost ALL (non amateur/commercial) stuff COULD theoretically land you in trouble! Not encourage "illegal activities" here too! Enforcing it with the thousands of Aircraft Band enthusiasts (At airports too) would be an impossibility tho! As a teenage SWL / radio enthusiast, I was always careful not to "transmit" anything. My late DAD worked as a GPO "Post Office" (now BT) Draughtman... Two in-law uncles... Engineer & Linesman! Having a criminal SON might have not been a good look for our family. lol The best advice is probably not to discuss *contents* of the transmissions? I still SWEAR some of the frequencies are a bit off, but...
  10. Great Stuff, Jim! In the world of social media, I find it good to hear that (what I call) "Grass Roots" science publicity... The Universities, National Laboratories and the Schools are still doing their STEM thing! I did visit Glasgow Physics Dept., back in '79 or so. Travelled there/back (train) from Manchester on a (freezing) FOGGY Winter day! A bit grim. lol. I quickly remark *many* University Campuses are now much changed... Yes, youngsters do quickly grasp the intricacies of "complex" sciences?
  11. Great stuff, MIke. Nice "random" (they are the best!) but useful conversation. 10GHz Eh? We are not worthy... etc. etc. For VHF monitoring I have (almost?) line of sight to Liverpool, Manchester & Blackpool ATIS from this (N.Wales coast) QTH. My excuse for "checking out" frequencies around 124 MHz! I can "cut bits off" these dipoles for "satellite". Interesting to compare my "wideband" Diamond X777 with the homebrew COAX "Double Bazooka" (I sense a "Carry On" film influence?). As hoped, its center 1/4 wave coax + wire 1/4 wave ends has a much bigger bandwidth! (Note change of scale).Though huge bandwidths may NOT be your desire... D777 "Aircraft": "Double Bazooka" Coax (Note wide bandwidht plus "better" SWR!) On the SDR1A and (Excellent) SDRUno software, I had noticed a possible drop in signal strengths??? I did a "Factory reset" and things seemed to get better. Something got "a bit confused" with my button pushings? AS A WEIRDER thing, some of my Aircraft frequencies are "Bang on"... Others (as reported!) are consistent 5kHz out! As we know, you are not (strictly) supposed to listen to A/C, but [IMO] there seems something weird re. (publically!) QUOTED frequencies of some Aircraft / Stuff??? The LOCAL 2m & 70cm repeaters are pretty much on expected freqs! I have tried to do a frequency calibration? MSF(?) on 60kHz still there. I don't SEEM able to hear WWV(?) on 2.5, 5, 10, 15, 20MHz though... Anyway, just more *random* thoughts for the fellow users/enthusiasts!
  12. Thanks All / both! Grist for t'mill -- I'll have a ponder anyway... For those who like to know "What others are doing"... Not a LOT in this WIND! But still making things in anticipation of better weather (and no Covid-19)! Below shows a Coax dipole of a "Double Bazooka" type using Electrial Duct parts! At left my Sirio 3000N Discone. At right some bits from https://www.barenco.co.uk/brackets-clamps Ultimately all/some of this is destined for up here... (X30N + TV antenna) But not JUST at the moment!
  13. I noticed that the CERN Atlas collaboration now make LHC data available to the Public! The claim is that high-school, undergrad and postgrad student (and enthusiastic self-learners) can have a go at being a "Particle Physicsist"?!? https://twitter.com/CERN/status/1227969676950458370 https://home.cern/news/news/knowledge-sharing/atlas-releases-13-tev-open-data-science-education https://atlas.cern/resources/opendata With a little prior knowledge I DID actually get it to "do something"! IF you are a STEM Teacher or Student you might like to have a go? Don't ask/blame me?!? But this might inspire some future scientist? P.S. If you are not at all serious, perhaps best not to click randomly. We probably don't want to bring CERN's computers to their knees!
  14. Just came across (via Brian Cox Tweet) latest VLT images of Betelgeuse! https://www.eso.org/public/news/eso2003/ Some amazing "before and after" animations knocking around too... https://twitter.com/Astro_MiguelM/status/1228369616646365184
  15. Great stuff @wxsatuser. Since we last spoke, I have been able to resolve (various HF band) FT8 transmissions that make no "waterfall" trace at all! As a random thought regarding VNA, my "tuned" longwire (via 4:1 Unun) gives great SWRs on the (traditional) HF bands: UNfortunately, when I add the COAX feeder: "All h*ll breaks loose" ROFL! I suspect the Coax outer functions as a counterpose / part of the antenna? Who Knows? I suspect that's why most HAMS favour tuned antennas! Things seem to be much easier at VHF/UHF where the feeder is "several" wavelengths long? At the moment I am thinking of doing a survey of all signals received locally on VHF/UHF, with the SIRIO (to 3Gz!) Discone! Looks like SUCH THINGS are a thing of active / serious research! Who knows? Will I be the oldest ever candidate for the RAE... Will I try do genuine "Radio Astronomy"... Or just receive satellite weather pics. As another GENERAL question, I am thinking of adding a G8FEK BBA3 50MHz-2GHz <1dB noise LNA to my kit of parts! Is the vendor active? Has anyone tried these LNA's (or similar)? Will a 30dB LNA completely overload my RSP1A/SDRUno? I sense another ASTRO "Money Pit". lol
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