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Re: MSF
Martin - G8JNJ
Hi,
It's on - you can check anytime via the SUWS WEB SDR.
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Re: MSF
It's on at the moment: my super antiquated Junghams Mega says so and it looks for a signal every hour. All modern MSF clocks only lock up once or twice in the middle of the night they so wouldn't "know" about, or show, any daytime outages. 'JNT
On 8 September 2016 at 12:49, 'Michael Scott' g3lyp@... [ukmicrowaves] <ukmicrowaves@...> wrote:
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MSF
Michael Scott
Hi All
Does anyone know if the MSF 60kHz signal is actually off the air? It was
scheduled to be off between 1000 – 1400 today, but both my RC clock and watch
show the presence of a signal.
73, Mike, G3LYP
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Re: Activity List for UK Microwave Group 24/47/76GHz Contest - Sunday 11th September
g4bao
It looks like everyone's too far West again but I can be available for tests from home on 24GHz on request. I'm QTHR and in the phone book so call me on the landline, via twitter @g4bao, email or find me on KST if you want a test. I might even be tempted to take my 24GHz /P system to Therfield IO92xa if anyone's in range and it's a nice day! Callsign: G4BAO Locator: JO02cg33 Band: 24GHz 1W 60CM Dish @8m AGL
On 7 September 2016 at 23:23, Keith Winnard gw3tkh@... [ukmicrowaves] <ukmicrowaves@...> wrote:
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Re: GB3SEE
Martin - G8JNJ
GB3SEE does seem to be off-air
Regards, Martin - G8JNJ www.g8jnj.net www.tc2m.info http://websdr.suws.org.uk
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Re: GB3SEE
g3thq <g3thq@...>
Yes, went off yesterday and still off
this morning (8 Sep 16). Heat related? 73 Brian NW London --
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Re: Activity List for UK Microwave Group 24/47/76GHz Contest - Sunday 11th September
Keith GW3TKH
Callsigns: GW3TKH/P & GW4HQX/P Locator: IO81LS19 Cefn Y Galchen Bands: ('TKH) 24GHz 0.5W 45cm dish, 47GHz 50mW 30cm dish, 76GHz ?uW 34dBi lens horn + G8CUB beacon tx. Bands: ('HQX) 47GHz 100uW 30cm dish, 76GHz ?uW 34dBi lens horn + G8CUB beacon tx.
Talkback: 144.175, mob: 07762 885015 Times: 10.00 BST onwards Keith GW3TKH
From: "g8cub@... [ukmicrowaves]" To: ukmicrowaves@... Sent: Wednesday, 7 September 2016, 14:04 Subject: [ukmicrowaves] Activity List for UK Microwave Group 24/47/76GHz Contest - Sunday 11th September With the last of the millimetre cumulatives contests this weekend. It has fallen on me to compile a list htis time. Please send details of your planned operation in the following format: Callsign: G8CUB/P Locator: IO81WU70 Birdlip, IO91CL12 Hackpen Bands: 24GHz 1W 20dB horn, 47GHz 30mW 30cm dish, 76GHz 50mW 150mm horn / 60cm dish Talkback: 144.175, KST maybe, mob: 07900 261121 Times: Birdlip ~ 10.00 -12.00, Hackpen ~13.00-15.00 BST The weather prediction looks hopeful at the moment, so looking forward to working you. Roger G8CUB
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Re: GB3SEE
g4uvz@...
Is SEE off again ?
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Second 5 GHz - 10 GHz satellite to launch
M5AKA
AMSAT-NA have already announced plans to launch a 5 GHz to 10 GHz amateur transponder payload into a Geosynchronous orbit https://amsat-uk.org/satellites/geosynchronous/na-gso-sat/ In addition they now plan to launch a 5 GHz to 10 GHz transponder satellite Heimdallr into Lunar orbit in September 2018. Trevor M5AKA AMSAT-UK http://amsat-uk.org/ Twitter https://twitter.com/AmsatUK Facebook https://facebook.com/AmsatUK YouTube https://youtube.com/AmsatUK ----
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Activity List for UK Microwave Group 24/47/76GHz Contest - Sunday 11th September
Roger Ray
With the last of the millimetre cumulatives contests this weekend. It has fallen on me to compile a list htis time. Please send details of your planned 76GHz 50mW 150mm horn / 60cm dish The weather prediction looks hopeful at the moment, so looking forward to working you. Roger G8CUB
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Re: Transmitter Linearity
I would argue that COFDM is not a way to improve weak signal performance. COFDM and all the related modulations have as a prime aim to optimise bandwidth usage in defined channels and make the best use of allocated spectrum. In data communications terms, they are generally referred to as "bandwidth-limited" modulation, making use of high order constellations like QAM and parallel stacked carriers themselves carrying QAM carrying . They are NOT weak signal modes in their own right. the need to conserve bandwidth automatically stops them having the best weak signal performance. The reason for the overwhelming popularity of multicarrier OFDM modes is their resilience to multipath as the resulting symbol rate of teh multiple parallel tones is far lower than the combined data rate of the complete information stram. In contrast, where bandwidth is not an issue but power or S/N is, we enter the realm of "power limited" modulation. And this is where most of amateur radio sits. But first of all you have to realise this does not just mean a wide signal bandwidth. "Bandwidth expansion" means a lot more than this in signal processing terms. Take as an example, repeating a messages (in SSB or Morse) five times to get it though. It has taken 5 times as long to transmit the same amount of source information . In a way you could say it has been expanded 5 times. In data there are other ways of doing it. You could expand the input data by adding error correction bits that increase it the same five-fold. That would result in a far-stronger error correction (getting the message through) than the 5 times repeat can offer. Back to modulation. We rarely need more than a few tens of bits per second for normal QSO traffic. Add very strong error correction which expands it say 5 times (and that is very strong indeed !) and you will get 100% copy at normalised S/N ratios (Eb/No) of around 2 to 5dB depending on the actual modulation type - PSK, FSK. But we are still only talking about a modulation that has to carry say 1000 symbols per second. And that will easily fit into a 3kHz spectrum. There's nothing to be gained in a pure additive noise environment by expanding further. In fact there are many purely practical advantages now of keeping modulation simple and using something like basic FSK to overcome the practicalities of transmitters - like linearity. Even if the result is wider than it need be. In spite of our reducing allocations, we still have a huge amount of spectrum to transmit a few hundred bits per second in. 3kHz arbitrary channelisation is still very wide in an AWGN environment. Difficulties come when we consider extreme microwave paths including rain scatter and EME scintillation. And that requires a complete rethink If we assume our signal is spread out to a few hundred Hz, that automatically limits our symbol rate permitted to a fraction of that, say a few tens of symbols per second. We cannot POSSIBLY send anything with symbols moving faster or even approaching the random shifts of the spreading. There's no hope of doing anything coherent So we need to choose a modulation that can send that on a scattered path. Its rather ironic, that the simplest modulation of its type, basic ON-OFF keying, is actually quite useful now. We look for the power change over the entire tone-band of the spread signal and integrate down to the symbol speed That way we look over a signal spreading bandwidth of say 200Hz but compress the result to say 10Hz. Pure ON/OFF is wasteful of transmitter energy. So we alternate between two tones, well separated in frequency to completely differentiate when the RS or scintillation or whatever, spreading occurs. By comparing one tone's averaged power per symbol against the other, 3dB advantage is gained over simple ON/OFF keying when transmitted peak power is compared [1] [2] By sending as one of, say, 64 tones instead of one of two, six information bits can be encoded at a time so for paths that give only a few Hz of shift (VHF and down) multi FSK is used To allow the symbol timing to be regenerated at the receiver, synchronisation signals have to be added to the symbols which reduces efficiency. For really good weak signal performance and recovery this could be as much as another 100% overhead. But we're still only at 2k symbols per second for standard QSO speed . For contest and routine Dx exchanges with limited info content we can go a lot slower - which means less source information in the same bandwidth. Or reduce the signal bandwidth further by still heaver signal processing. The weak signal WSJT modes take all this into account and I think really do represent the best we are going to get on the amateur bands for weak signal Dx type working. They don't support real time waffle type QSOs, where RTTY and PSK31 would be used, but for contest and EME exchanges and pre-formatted messages can't be beaten All the weak signal ones use multi FSK of 4, 9 or 65 tones with tone spacing options that can be chosen for the path. They all have a large overhead for synchronisation allowing for reliable lockup based only on a search in time and frequency over a limited range. Up to recently that have all used similar error correction coding, JT4, JT9 and WSPR all use convolutional coding with about three times expansion of the number of bits. JT65 does it differently eiht Reed Solomon and its resulting six-symbol MFSK. But they all have a similar performance in terms of normalised S/N (Eb/No) needing about 4dB in their respective symbol bandwidths ranging from 1.5Hz for WSPR to 4.4Hz for JT4. That puts it within about 4 dB (very roughly) of Shannon's theoretical limit for this modulation type. The latest change is a completely new error correction coding in the latest version of WSJT, called QRA64. The encoding is simpler than JT65, it is sent using the same modulation - one of 64 tones with a reduced synchronisation overhead The clever bit comes in the decoding. It is now believed to be within 0.6dB of the theoretical limit of Shannon limit for incoherent (FSK type ) modulation. [1] When you consider Tx MEAN power, two tone FSK and .OOK have identical performance. The only difference being, you need a 200 Watt Tx, half on and half off, to equal a 100 Watt Tx sending FSK at 100% duty cycle. Same mean, 3dB peak difference) [2] Coherent modes like PSK and QAM are inherently capable of better S/N performance than incoherent FSK. In fact, under ideal conditions exactly 3dB better. Comparing two antipodal voltages for BPASK instead of power in two tone freqeuncies. But coherency is complicated by the need for carrier recovery and phase locking, then symbol timing. The non linear processing needed for that, in a really weak signal situation with fading , multipath etc makes it a worse choice than keeping things simple and using non-coherent FSK. Hence, why the all the WSJT modes for weak signal use use MFSK Andy G4JNT
On 7 September 2016 at 08:19, 'Chris Bartram' cbartram@... [ukmicrowaves] <ukmicrowaves@...> wrote:
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Re: Transmitter Linearity
F6DRO
Hi agn ,
the Constant amplitude ssb modulation system did not raised comments it looks: http://www.ve6aqo.com/images/roel030406_beacon/PAoJTA%20PLL%20SSB.jpg It can be done in software in a sdr transmitter , but I'm not sure , because I have not looked at it in detail ,that the statement this modulation can be with frequency multipliers is true. If yes , it is a simple way to get some power on 47Ghz for exemple 732 Dom
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Re: Transmitter Linearity
Wolfgang Hoeth OE4WOG
fully agree to this statement, as the number of active Microwavers steadily increase, we must pay more attention to the signal purity of LO`s and PA`s on our microwave gear. 73, Wolfgang, OE4WOG ------ Originalnachricht ------
Von: "'dominique.dehays' Dominique.DEHAYS@... [ukmicrowaves]" <ukmicrowaves@...>
An: ukmicrowaves@...
Gesendet: 07.09.2016 09:36:20
Betreff: Re: [ukmicrowaves] Transmitter Linearity Hi agn , yes , I think it's never a good idea to say : let's go dirty , it would'nt hurt anyone. The exemple I took with RS can be extended to tropo as well. The activity level on 3cm requires we stay clean 73 Dom
Le 07/09/2016 09:19, 'Chris Bartram'
cbartram@... [ukmicrowaves] a écrit :
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Re: Transmitter Linearity
F6DRO
Hi agn ,
toggle quoted messageShow quoted text
yes , I think it's never a good idea to say : let's go dirty , it would'nt hurt anyone. The exemple I took with RS can be extended to tropo as well. The activity level on 3cm requires we stay clean 73 Dom
Le 07/09/2016 09:19, 'Chris Bartram'
cbartram@... [ukmicrowaves] a écrit :
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Transmitter Linearity
Chris Bartram <cbartram@...>
FWIW, I accept that running an SSB transmitter well PA into compression isn't likely to cause the world to stop turning! However, I prefer to try to run my SSB transmitters linearly, rather than waste energy by spreading it across the band.
The real prize which comes from the use of more linear transmitters is the potential ability to use more effective modulation schemes than SSB, CW, or constant amplitude data. I have heard credible suggestions that the way to improve the weak signal performance of amateur radio (data) systems over real-world microwave paths is to use COFDM with wider bandwidths than the 2.3kHz occupied by SSB. This however requires a much more linear transmitter than most of us currently have. Practically that means the use of linearisation, and a software derived exciter. Vy 73 Chris GW4DGU/A
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Re: The full email - TGA2760
SAM JEWELL
Of course when RS signals are that strong who can tell what the SSB sounds like anyway? Time to go CW.......narrower. Or go FM? 😊 73 de Sam, G4DDK
On 6 Sep 2016, at 12:45, 'dominique.dehays' Dominique.DEHAYS@... [ukmicrowaves] <ukmicrowaves@...> wrote:
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Re: The full email - TGA2760
F6DRO
Hi ,
looks like we don't live in the same galaxy, I can tell U we care , during a RS opening there are something like 10 stations on the band and some with absolutely outstanding levels During a good event signals from Paris and Beauvais , close to 700km away are 9++++++++ , this is then we decide to try 24Ghz RS 73 Dom
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Re: The full email - TGA2760
And do we really care about the sidebands on an SSB signal on 10GHz? Even in the biggest events from a hilltop site , you're unlikely to hear more than two stations simultaneously. Back in the 1990's when many of us ran TWTs, running them well into compression was common, and no one complained. 'jnt
On 6 September 2016 at 11:49, 'dominique.dehays' Dominique.DEHAYS@... [ukmicrowaves] <ukmicrowaves@...> wrote:
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Re: The full email - TGA2760
F6DRO
Hi all ,
what about constant amplitude ssb? It was promoted a long time ago , and was sadt to be very interesting too for high bands microwaves at it was possible to use a varactor multiplier with a SSB tx. I recall in the 70's the late F1ANH using this modulation mode to avoid detection of the surroundings neighbours TVs 73 Dom
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Re: The full email - TGA2760
Chris Bartram <cbartram@...>
Hello Neil
There is a third alternative to linearising PAs. It's quite possible to use an analogue lineariser to compensate for PA non-linearities. It doesn't work as well as adaptive linearisation, as the transfer characteristics of the PA, both in amplitude and phase, won't be static with time and temperature, but for typical amateur SSB operation it would probably be good enough! One thought is that for SSB, this could be done at audio. Incidentally, predistortion does not involve a conventional negative feedback mechanism, (The term 'adaptive feedback' which I seen in amateur literature is very misleading. Feedback linearisation of amplifiers is a very different process.) as there is far too much latency in the necessary processing. Rather the predistortion operates to adjust the signal path outside the modulation bandwidth. I can't imagine that manufacturers like ELAD aren't working on predistortion schemes. It's not a trivial task, but the improvement in performance which can be obtained is spectacular. Despite some opposition, I encouraged the maker of some PAs I designed a few years ago for the amateur VHF bands to incorporate a sampling port for adaptive feedback, and the results have been very good. Don't forget though, that you need to incorporate an extremely linear downconverter sharing a common transverter LO to make good use of adaptive linearisation. Vy 73 Chris GW4DGU/A
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