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@M0YNG I just used the Add Media icon. Testing it with a JPEG now:

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@M0YNG I just used the Add Media icon. Testing it with a JPEG now:

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@M0YNG There is a very fast wideband splat as the blades reach vertical and you get doppler at a wide range of frequencies over a few hundred milliseconds, with reflection from each bit of the blade. Sometimes the shift is as much as 10.5kHz. I tried to upload a static GIF. That didn't work as the system was expecting an animated GIFG I expect. I tried an MP3, but it said the format was not recognised. MP4 was a bit odd, it accepted the upload but nothing appeared

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@M0YNG There is a very fast wideband splat as the blades reach vertical and you get doppler at a wide range of frequencies over a few hundred milliseconds, with reflection from each bit of the blade. Sometimes the shift is as much as 10.5kHz. I tried to upload a static GIF. That didn't work as the system was expecting an animated GIFG I expect. I tried an MP3, but it said the format was not recognised. MP4 was a bit odd, it accepted the upload but nothing appeared

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Tutorial on VHF/UHF/SHF propagation by Mike Willis always worth a repost http://www. mike-willis.com/Tutorial/PF6.h tm

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Tutorial on VHF/UHF/SHF propagation by Mike Willis always worth a repost http://www. mike-willis.com/Tutorial/PF6.h tm

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recorded from Elad FDM-SW2 and my Elad FDM-DUO using the XBox Live utility in Win10

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recorded from Elad FDM-SW2 and my Elad FDM-DUO using the XBox Live utility in Win10

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OK, that failed as well. non-animated GIFs fail, MP3 and MP4s fail. Links perhaps? http://www. g4dbn.uk/?p=860

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OK, that failed as well. non-animated GIFs fail, MP3 and MP4s fail. Links perhaps? http://www. g4dbn.uk/?p=860

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Listening to the weird windfarm doppler from GB3FNY on 10368.752MHz, coming through two turbines 10km away. Let's see if the MP4 will upload. The MP3 failed

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Listening to the weird windfarm doppler from GB3FNY on 10368.752MHz, coming through two turbines 10km away. Let's see if the MP4 will upload. The MP3 failed

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@m0pcb once you get your head round it, it works well. (23cm 7-16 DIN to reduced-height waveguide transion for slot array)

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@m0pcb once you get your head round it, it works well. (23cm 7-16 DIN to reduced-height waveguide transion for slot array)

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@M0YNG yep, good call. Could be the inverter has died rather than the CFLs, so LED strips might be better solution. This thing must have been really expensive when it was new. You can still get it fixed by Agilent, but I could buy another for that price

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@M0YNG yep, good call. Could be the inverter has died rather than the CFLs, so LED strips might be better solution. This thing must have been really expensive when it was new. You can still get it fixed by Agilent, but I could buy another for that price

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Dammit, *BOTH* of the CFL backlight lamps on my Agilent E4406A VSA speccy analyser have died. Time to tear the case open and see if I can find a CFL the right size. Lucky the old HP 8562A with the CRT is still chugging away

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Dammit, *BOTH* of the CFL backlight lamps on my Agilent E4406A VSA speccy analyser have died. Time to tear the case open and see if I can find a CFL the right size. Lucky the old HP 8562A with the CRT is still chugging away

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@moddedLimes yep, this was purely designed as a transmit LPF, no use at all for the specific use-case of a receive front end. I use the three-post interdigital filter from Aerial Parts of Colchester. Don't want to put that at the masthead though

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@moddedLimes yep, this was purely designed as a transmit LPF, no use at all for the specific use-case of a receive front end. I use the three-post interdigital filter from Aerial Parts of Colchester. Don't want to put that at the masthead though

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@moddedLimes @M0YNG but I'm sticking with 1960s machining technology for now!

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@moddedLimes @M0YNG but I'm sticking with 1960s machining technology for now!

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@moddedLimes I used the excellent design sheet from F1FRV, which handles all of the fringeing and end termination issues. Other option is to use a proper EM solver. Might be feasible in OpenEMS. I used that to do the design for a 23cm N-type to reduced-height-waveguide model which worked fine, but you need to have some knowledge of Octave

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@moddedLimes I used the excellent design sheet from F1FRV, which handles all of the fringeing and end termination issues. Other option is to use a proper EM solver. Might be feasible in OpenEMS. I used that to do the design for a 23cm N-type to reduced-height-waveguide model which worked fine, but you need to have some knowledge of Octave

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@moddedLimes yep, lots of possibilities. The surface only needs to be smooth at the micro scale, macro lumps don't matter much, it is about surface resistivity and skin depth. Also if you use a fine PLA, you can make an investment casting in ally, and the surface tension of the liquid will smooth out any small imperfections so long as you burn the PLA out at high enough temp.

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@moddedLimes yep, lots of possibilities. The surface only needs to be smooth at the micro scale, macro lumps don't matter much, it is about surface resistivity and skin depth. Also if you use a fine PLA, you can make an investment casting in ally, and the surface tension of the liquid will smooth out any small imperfections so long as you burn the PLA out at high enough temp.

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@moddedLimes I'd worry about surface finish though, the top 5 micrometres needs to be very smooth and highly conductive to get the unloaded Q into the 20,000-40,000 range. Machining from solid aluminium billet isn't too hard, but a 3D printer is certainly 1/100th of the price of a CNC mill!

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@moddedLimes I'd worry about surface finish though, the top 5 micrometres needs to be very smooth and highly conductive to get the unloaded Q into the 20,000-40,000 range. Machining from solid aluminium billet isn't too hard, but a 3D printer is certainly 1/100th of the price of a CNC mill!

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@moddedLimes see http://www. g4dbn.uk/?p=517

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@moddedLimes see http://www. g4dbn.uk/?p=517

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Maybe something like the right-hand end of this pic with two or three cavities would be sharp enough and <0.3dB insertion loss? Tricky without a CNC mill, but a rotary table and Bridgeport might do the job. Failed as a GIF, trying as a JPEG...

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Maybe something like the right-hand end of this pic with two or three cavities would be sharp enough and <0.3dB insertion loss? Tricky without a CNC mill, but a rotary table and Bridgeport might do the job. Failed as a GIF, trying as a JPEG...

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oh weird, that pic doesn't appear...

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oh weird, that pic doesn't appear...

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Today's engineering challenge is to come up with a front-end 1.3GHz filter to notch out DTV on to 600-800MHz band and also 3G/4G cellphone trash, to prevent front-end overload from out of band signals. Question is whether milled post-cavity resonant cavities can do the job, or if a sharp high-pass filter plus a notch would be mechanically easier. LPFs are easy, see pic of one I made earlier, but HPF/notch not simple.

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Today's engineering challenge is to come up with a front-end 1.3GHz filter to notch out DTV on to 600-800MHz band and also 3G/4G cellphone trash, to prevent front-end overload from out of band signals. Question is whether milled post-cavity resonant cavities can do the job, or if a sharp high-pass filter plus a notch would be mechanically easier. LPFs are easy, see pic of one I made earlier, but HPF/notch not simple.

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@M0YNG I kind of assume that only radio-related stuff will be posted by my account on here. Politricks and teh Cyberzz will be auto-muted at source, using taste and judgment controls which might not be engaged on the birdy site. Self-censorship in fact, although I might slip into machinist or antenna pr0n at times

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@M0YNG I kind of assume that only radio-related stuff will be posted by my account on here. Politricks and teh Cyberzz will be auto-muted at source, using taste and judgment controls which might not be engaged on the birdy site. Self-censorship in fact, although I might slip into machinist or antenna pr0n at times

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@MU0WLV @M0YNG we are sad and old and crusty, us geefers. In real life I'm a crusader against Russian cybercrime gangs and nation-state threat actors, but on here I hack stuff and mess about with radios for fun.

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@MU0WLV @M0YNG we are sad and old and crusty, us geefers. In real life I'm a crusader against Russian cybercrime gangs and nation-state threat actors, but on here I hack stuff and mess about with radios for fun.