Different lenses/material have other phase points , so I agree with DD4YR 's remark .. try to tweak the LNB position to max signal (to noise ratio)
Posts by PA3FYM
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oh2aue These frequencies are too close. I meant the 1200 MHz and (say) 1575 MHz range.
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oh2aue Nice plots. Do you have an example/photo of these dual band patches? E.g. for GPS L1-L2, or Gal E1 - E5 ?
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dj0abr or .. Obstler ; -)
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G0MJW (I know that you know, but the picture was merely intended for other readers ; -)
Unlike science, the radio amateur community doesn't have a 'memory', so reinventing wheels and making 'new discoveries' is a 'mandatory part' of our hobby ; -)
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oh2aue Merry CPhristmas ; -)
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My goal is to make as few turns as possible so as not to shade the LNB.
dj0abr That is -generally speaking- not a good idea because a helix starts to produce CP (with good/sufficient axial ratio) after 4 turns or so. Just model it in antenna modelling software (like 4NEC2) and you'll see.
G0MJW Yes, the same goniometry / math is also valid for offset dishes. An offset dish is nothing else than a prime focus dish but then another part of the parabola. The higher you get into the parabola, the larger the f/D. Although the illumination may look optically 'squint', the effective surface of an offset dish is equal to a 'prime focus dish' with the diameter of the width of the offset dish, see below.
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oh2aue Nice elaboration Michael : -) Perhaps you can measure a POTY with your polarimeter? I am curious how your CRT displays the results : -)
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dj0abr : It is still valid, because it's a matter of goniometry ; -) For a f/D = 0.6 dish you need a -10 dB opening angle ('Offnungswinkel') of 90 degrees, see here: https://twitter.com/remcodenbe…tatus/1091974633111388160 and here: https://twitter.com/remcodenbe…tatus/1073501855869792257
For lower f/D's the angle has to become bigger, so less turns. It's easy to simulate with e.g. 4NEC2. Doing this you can derive the 1 winding per 0.1 f/D unit (it's not f/D unit, but 0.1 f/D unit, sorry for the typo in my previous post).
And .. 150cm, is that the offset dish length or the width? With offset dishes one always has to take the width as 'effective surface'.
So, regardless of the diameter of your dish, you still need a -10 dB 90 degree opening angle for a f/D=0.6 dish --> 6 windings .. because of mathematics/goniometry ; -)
However, for transmit purposes perfect illumination is not necessary, because it can be compensated with extra 'earth power', so therefore people using less turns are not 'punished' or not knowing that they are 'punished' ; -)
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G0MJW : There are a few articles on DJ7GP's feed (iirc in Funkschau) by DJ7GP himself, where he also states that its CP isn't ideal.
I made one almost exactly one year ago with a 'FYM-mod' (additional screw) but at that time Mike and I found each other to converge to something more simpler which was baptized POTY on 3 March 2018 ; -)
G0MJW : for the DJ7GP dimensions (omit the FYM screw) see: https://pbs.twimg.com/media/Du…lzH?format=jpg&name=largeAnd also these Twitter posts:
https://twitter.com/remcodenbe…tatus/1075873782416445440
https://twitter.com/remcodenbe…tatus/1075446385170890752
A year has gone by .... ; -)
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DF1QE Yep, the load capacitance of the xtal may be optimized for accurate frequency, but .. what the heck ; -)
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DF1QE Sorry, unfortunately this method of injecting already has been done (by me) long time ago. So, it's (c) PA3FYM . . . (until others prove they were earlier ; -)
Let me look it up ...
Yes... found it, here it is. I published it even before QO-100 was officially operational, on Jan 27th:
https://twitter.com/remcodenbe…tatus/1089522884404527104 -
DF1QE Yes, I also built these push pull oscillators ('Gegentakt') at very young age for FM with ECC85 etc. Output was ca. 5W.
Here (i.e. Hilversum region) called that oscillator a 'Kalitron' and we used 'Butterfly' capacitors from Philips army equipment.About the injection of the LO. A friend of mine, who designed LNB's for Philips in the 80 - 90's told me about the symmetrical injection and its positive effect on phase noise in NXP (former Philips) (TFF) chips.
Based on this information and the fact I was donated a LNB with a NXP chipset I tried to convert my friends hint into a practical solution.
Glad that it's of use for/to you : -)
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The 'Bamatech Horn' is actually an 'open' waveguide, so suitable for f/D's up to 0.45. When having a f/D > 0.45 the waveguide needs 'some focussing' to illuminate the dish so that the -10 dB points of the lobe coincide with the (horizontal) edges of the (offset) dish. Either a horn or dielectric lens may be a solution. (such as developed and deployed in zillions of broadcast LNB's ; -)
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Think I´ve missed so far: CN, EL, 4U1ITU and 3A (if it was really QRV via QO-100
).I certainly missed 4U1ITU and ZA/DL2RMC. People told me 3A was active, but hitherto I can't get a confirmation 3A was/has been really active.
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#86 DXCC here and 333 grid locators . . .
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POTY is the Patch Of The Year, which the Bamatech antenna is NOT.
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4Z4LS Achtung ! (the (Russian) letters on your avatar...) These calculations / 'inventions' have been made several months / years before.
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pe1hzg No NDA this time: I don't know.. but for commercial transponders, they can actually do geolocation of any uplinking stations to a scary degree of precision.. maybe it's linked to that.
Indeed, malicious uplinkers (pirates) can be geolocated with TDOA-like techniques in collaboration with other satellites.
Forthermore, there is no 'GPS' to ascertain the exact position of the satellite, so it has to come from internal references, e.g. Cs- (in conjunction with Rb-) standard(s). -
St2nh Nader, that is a very old publication from me, I think almost 20 years old ; -) It was intended as 'WLAN' antenna.
In order to illuminate an offset dish properly with a helix, there is a rule of thumb saying: 1 turn for every 0.1 f/D.So in order not to over illuminate the dish, make another helilx with 6 turns, as most commercial broadcast dishes have f/D's of around 0.6.
