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61
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eHam Forums / Elmers / A good frequency counter kit
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on: January 01, 2011, 04:09:59 AM
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Hi,
A very happy New Year to all.
My old frequency counter has gone mad, showing erratic display.
Thought of buying a kit. Need some good advise as to which is available in terms of :
1. Stable count, no varying digits.
2. sensitive input, low level input
3 .Down to audio frequencies ( not all counters are efficient here )
4. Up to as many Mhz as I can imagine, although I do not work much above say 500 Mhz.
5. Does it really needs to be PIC controlled ?
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62
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eHam Forums / HomeBrew / Wanted
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on: December 02, 2010, 03:56:58 AM
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Wanted: The hf downconverter of the R2pro, in kit or assemled form, also
some components like the LC diplexer coils and capacitors for the same kit.
Paul
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63
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eHam Forums / HomeBrew / Switching frontend mixers
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on: December 01, 2010, 02:11:55 AM
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The Tayloe or H mixer can be fed from the third harmonic of a local oscillator, to facilitate using a low frequency local oscillator. Does this technique produces any losses, as against using the fundamental lo frequency ?
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64
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eHam Forums / Elmers / Tayloe or H frontend mixer
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on: December 01, 2010, 02:10:52 AM
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The Tayloe or H mixer can be fed from the third harmonic of a local oscillator, to facilitate using a low frequency local oscillator. Does this technique produces any losses, as against using the fundamental lo frequency ?
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67
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eHam Forums / Mods And Repairs / TS850 FAQ
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on: November 04, 2010, 10:25:52 AM
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Hi all,
I have a TS850 sat European model.
How can you tell the manufacturing date from the serial number ?
Also, what other info can be decoded from the serial number ?
Can I modify to cover beyond 7.1Mhz ?
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68
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eHam Forums / Elmers / SDR Radios & soundcards
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on: August 28, 2010, 06:47:26 AM
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HI all I am starting experimenting with software defined radios. I have a SIS 7018 sound card, but unable to source its specifications. Cannot tell if it is a duplex, and which sampling rate, if 48 or 94 Khz Can anyone please point a web resource, or has some info about this chip Thanks __________________ Paul 9H1FQ An unknown gem of the Mediterranean sea is the Island of Malta. blessed with warm sun , all year round. In just one day, you can see places which will make you travel in history from the Prehistoric temples throu the middle ages, the Knights of Malta, all the way to world war two. All the major civilizations have left an imprint on this lovely little island. There is so much to see and enjoy the excellent weather. official website http://www.visitmalta.com/main?l=1Weather: http://www.maltaweather.com/fiveday-forecast.htmlhttp://www.maltaweather.com/climate.shtmlhttp://www.thomson.co.uk/holiday-wea...-in-malta.html |
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69
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eHam Forums / Elmers / 50 ohms or 75 ohms ????
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on: August 19, 2010, 03:02:52 PM
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One of the questions I was asked for my RAE amateur radio examination in 1964, was : What is the centre impedance of a half wave dipole at 7mhz , a quarter wave up. And the correct answer THEN was 75 ohms. Nowadays its 50 ohms- How come  ? Paul |
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70
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eHam Forums / Elmers / NIMH charging circuit
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on: July 26, 2010, 07:52:45 AM
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Hi all,
I have four NH15-AA 1.2 Volts NIMH batteries.
I am completely ignorant about these kind of batteries.
I tried to charge them with an ordinary walplug psu, to no success.
I have lots of transformers and walplugs, but what sort of charger do I need constant current or voltage ? How much charging voltage they withstand ? Charge them in series ?
Any web resources for a simple charging circuit please !
Paul
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72
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eHam Forums / Elmers / LO level match on the MC1496
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on: July 25, 2010, 09:30:28 PM
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Hi all,
I have a DDS VFO, with some 14db amplifier at 50 ohms.
I need to feed this vfo to two mixers, one is a TUF-3 diode bridge, and the other an MC1496 double balanced modulator.
I will be using a 50 ohms unequal resistive power splitter. It is ok for the TUF-3 mixer, as I can feed it with +7db at 50 ohms.
The problem is with the MC1496. The spec sheets do not specify the input impedance of the LO injection pins 8 & 10, they only specify an ideal carrier input of 100 mV. No mention is made of the input impedance.
In another circuit, the MC1496 LO input is being fed from a BC548 transistor, with a 280 ohms emitter resistor, an 8.2k from +12 to base and 3.3k from ground to base, with a matching transformer at the collector six turns primary and three turns secondary on ferrite bead.
Shall I terminate the unequal power splitter with 50 ohms an feed the MC1496 as if is is a medium to high impedance ?
Paul
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73
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eHam Forums / HomeBrew / cathode follower
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on: July 19, 2010, 02:30:50 PM
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Hi all,
I have an old TE-20 valve signal generator. The output is taken from a variable resistor on the cathode, with an unknown variable impedance.
Can I make it 50 ohms output, by simply adding the usual bifiliar transformer. If so, can I just put it in series, between ground and cathode, or by a coupling capacitor from the cathode resistor ?
Paul
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75
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eHam Forums / Elmers / cathode follower impedance
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on: July 18, 2010, 10:25:06 AM
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Hi all,
I have an old TE-20 valve signal generator. The output is taken from a variable resistor on the cathode, with an unknown variable impedance.
Can I make it 50 ohms output, by simply adding the usual bifiliar transformer. If so, can I just put it in series, between ground and cathode, or by a coupling capacitor from the cathode resistor ?
Paul
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