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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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13th Jun 2019, 4:29 pm | #1 |
Tetrode
Join Date: Apr 2014
Location: Essex, UK.
Posts: 70
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Microwave Modules 70cms Converter to 28 MHz
Does anyone know what the 404 MHz LO port measures into 50 ohms or open circuit like a high Z scope?
Thanks Kevin |
14th Jun 2019, 7:54 am | #2 |
Heptode
Join Date: May 2008
Location: Selby, North Yorkshire, UK.
Posts: 951
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Re: Microwave Modules 70cms Converter to 28 MHz
What is the mixer device used?
If it's a sealed DBM like an SBL-1 etc, then they typically specify 5-7dBm LO input level. I suspect though it might be a discrete device?
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14th Jun 2019, 7:59 am | #3 |
Heptode
Join Date: May 2008
Location: Selby, North Yorkshire, UK.
Posts: 951
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Re: Microwave Modules 70cms Converter to 28 MHz
There looks to be the circuit diagram available on the website of G4KFK
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14th Jun 2019, 9:07 am | #4 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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Re: Microwave Modules 70cms Converter to 28 MHz
Isn't that port an output? Useful for incorporating the converter into a transverter?
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14th Jun 2019, 11:25 am | #5 |
Tetrode
Join Date: Apr 2014
Location: Essex, UK.
Posts: 70
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Re: Microwave Modules 70cms Converter to 28 MHz
LO port is at 404 MHz, it is an additional output.
Kevin |
14th Jun 2019, 11:31 am | #6 |
Tetrode
Join Date: Apr 2014
Location: Essex, UK.
Posts: 70
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Re: Microwave Modules 70cms Converter to 28 MHz
Mixer is a 3N204
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14th Jun 2019, 4:30 pm | #7 |
Tetrode
Join Date: Apr 2014
Location: Essex, UK.
Posts: 70
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Re: Microwave Modules 70cms Converter to 28 MHz
Can't find the circuit of my particular unit, MM documentation is a bit random!
LO Output is -1 to-3 dBm depending on supply voltage, probably ok. But the overall conversion gain is only 15 dB and noise figure too high. Compared to another/later 70 cms MM converter, sensitivity is -120 dBm for 10db s/n against -126 dBm for the good one, which has a gain of 25db. This one has a better front end, a BFR34 transistor but it doesn't sound like the BFY90 front end of the faulty one is the source of the fault. Kevin |
15th Jun 2019, 9:14 pm | #8 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,015
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Re: Microwave Modules 70cms Converter to 28 MHz
Maybe expecting too much for a BFY90? They beat a BF180 in a PYE PF1RX but they were not that good.
Conversion gain of 15dB is OK for anything except a deaf 28MHz IF. If the IF is not that sensitive it will appear that the NF is high instead - even if it isn't in reality. If this is the die-cast box RX only version, rather than a transverter, then I have one too. It hasn't been on for years but maybe I could still find it. |
16th Jun 2019, 6:40 am | #9 |
Tetrode
Join Date: Apr 2014
Location: Essex, UK.
Posts: 70
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Re: Microwave Modules 70cms Converter to 28 MHz
I recall the BFY90 has a NF of 5dB or so at 70cms, so not great. I would expect the sensitivity was better maybe -123dBm not -120. There were at least 2 versions of 70cms converter, the LO one and the one with 2 switchable crystals. Latter measures better at 2.5 dB NF, 25 dB conversion gain.
Kevin |