G8JNJ
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- G8JNJ
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Hi Ron, If you want to build a FET amplifier that is likely to work properly, take a look at this design which uses ST PD85004 http://www.qsl.net/in3otd/ham_radio/PD85004_PP_PA/PD85004_PP_PA.html http://www.qsl.net/in3otd/ham_radio/PD85004_PP_PA_I…
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This is the Trimble antenna I'm using. http://www.trimble.com/timing/bullet-40dB-antenna.aspx It's powered by a Trimble Thunderbolt, but the antenna is passively split four ways (introducing a further 6dB loss) and connects to the KiWi's via 20m of…
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Hi Ron, A couple of weeks ago I received a private email about this circuit, and decided to make a copy, as the person who wrote was having problems with it, and I couldn't figure out how the circuit could perform as described. I found that the IMD …
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Hi Marco, I have a selection of active antennas running on my KiWi, including some LZ1AQ loops and other whips etc. Which can be chosen using the antenna switching extension. http://southwest.ddns.net:8073/?ext=ant_switch Antenna 5 is a Trask desig…
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Hi Ron, The 2N2222 seem to provide the lowest value of input resistance from the types that I have tried. For the output pair, almost any NPN transistor with a power dissipation of approx 1w and a FT greater than 1GHz should be fine. Regards, Marti…
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Hi John, Ah OK that makes sense. I'm seeing the search rather than an actual sat. Regards, Martin - G8JNJ
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Hi John, I can see Q 201, 199, 198, 197, 195, 194, and 193 very occasionally (fleeting) appearing on my KiWi in the SW UK however I don't know if these are valid signals or false decodes. I'm using a Trimble 'mushroom' antenna (mounted outside and w…
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Hi Ron, It's basically two Norton lossless feedback amplifiers connected in a push pull arrangement. The winding in the emitter circuit provides negative feedback and the ratio of the windings sets the amount of feedback and therefore the overall ga…
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Hi Kenneth, I've also had similar problems in the past. If you still have problems when you try using a new card, check your power supply. The Beagle seems to need to draw a higher peak current when writing to the card and if your PSU / DC cable is…
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Hi, Some more information relating to previously used amateur methods for receiving Ionosondes here http://jcoppens.com/radio/prop/g3plx/index.en.php Regards, Martin - G8JNJ
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Hi Ron, OK - if that's a problem you need to use much bigger value capacitors :-) Regards, Martin - G8JNJ
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Hi Ron, Good stuff. I'm assuming that you made the PSU noise floor comparisons with the bias tee in circuit, but without the antenna connected ? Regards, Martin - G8JNJ
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Hi Ron, I find your comment "Then the noise floor and images drop down to an acceptable level." interesting. I suspect that the wide bandwidth of the Hiletgo LNA may be a problem and that it is VHF and UHF broadcast stations that are overl…
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Hi Ron, I think you could either center tap the input transformer on the loop side (prefered method), or add two 1K Ohm value resistors (or similar) from either side of the loop / transformer connection to ground. Regards, Martin - G8JNJ
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Hi Ron, My guess is that you have inadvertently scraped some of the enamel insulation off the transformer winding(s) at some point, as it's very easy to do this. I use Kynar insulated wire (the type sold for wire wrapping) wherever possible, as this…
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Hi Ron, You raise an interesting point regarding the noise contribution from three terminal voltage regulators. This topic was covered in some detail in the March 2018 issue of RADCOM (p76-77), the member's magazine pubilshed by the Radio Society of…
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Hi Ron, All good. I had to hand select balanced pairs of transistors for my Wellbrook clone. Be careful about reducing the voltage too low as the IMD will suffer. I generally find that most designs will work OK down to about 8v, maybe 5v if I'm luck…
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Hi Frans, I'd agree with John, all my 'strange' KiWi problems eventually turned out to be associated with the DC power supply and / or connecting cable. * No boot from cold * Reset button not initiating a reboot * Occasional loss of Ethernet conne…
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Hi, The GPIO pins that are currently used by the KiWi ant_switch extension are as follows:- P8 pin 11 - GPIO_45 - Antenna 1P8 pin 12 - GPIO_44 - Antenna 2P8 pin 13 - GPIO_23 - Antenna 3P8 pin 14 - GPIO_26 - Antenna 4P8 pin 15 - GPIO_47 - Antenna 5P8…
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Hi Ron, That looks pretty much as I'd expect it to. If you take a look at my KiWi (zoomed out to WF0) http://southwest.ddns.net:8073/?ext=ant_switch Switch between antenna 4 (LZ1AQ loop low input Z amp) and antenna 7 (G8JNJ loop with higher input Z …
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Hi Ron, You have got a few parameters interacting. With most unscreened broadband loops of about 1m diameter, the predominant loop impedance is mainly a low resistive value. So amplifiers with a low value of resitive input impedance such as the Well…
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Hi Ron, The LZ1AQ loop amplifier kit uses CAT6 for power, control and signal. http://active-antenna.eu/tech-docs/2_ActiveAA_Mount_21.pdf CAT 5 & 6 has a characteristic impedance of 100 Ohms per twisted pair. You can build an impedance matching…
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Hi John, I've now spent a bit more time playing with this application. It's not the easiest thing to setup or initially use, but it does have some quite impressive features such as the ability to import various online databases and parse .xlsx files…
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Hi Ron, I think the loop is still unbalanced. The split is to avoid a continuous 'screen' (Faraday screen to minimise E-Field pickup) around the loop. But if one end of the center conductor is connected to ground you may have a problem. Check signal…
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Hi Ron, Bias tee's are not as simple as they seem at first sight. The trick is to use a lossy ferrite so that you don't get a very high value of Q which could lead to unwanted resonances. The core also has to be big enough so that it doesn't saturat…
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Hi John, The change has made a huge difference no sign of any audio 'stuttering' and a very fast and smooth scroll up and down in frequency at all zoom levels. Thanks for that :-) Regards, Martin - G8JNJ
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Hi John, Quite a few 170Hz / 100bd FSK signals I've heard (but not decoded) turn out to be "Digital selective-calling system for use in the maritime mobile service" using a ten-bit error-detecting code. All of the code structure is def…
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Hi John, I like the new shift markers that makes things a lot easier :-) Would it be possible to stop it e-zooming to WF 12 when a new shift is selected ? Or alternatively zoom to WF 13 or 14 when very narrow shifts are selected ? Rivet looks to be…
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Hi Steve, Mine's pretty flat from a few KHz up to 30MHz. The problems most folks have are 'hedgehogs' of spikes at regular intervals, usually peaking around specific frequencies. These are generally originating from specific bits of kit such as swit…
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Hi Steve, What mode and bandwidth are you using when you measure the noise floor ? It shouldn't change from when a load is connected directly to the KiWi and when connected at the far end of the coax in place of the antenna. If it does you have a pr…