Re: New 10 GHz LNB
Posted: Sun Dec 02, 2018 8:57 am
I don't really want to use my Leo-Bodnar permanently for EsHail as it is so useful for other things. I have researched other solutions to the 25 MHz reference.
Firstly, you don't really need to lock to GPS. A very good solution would be to take a good 100MHz ovanised reference oscillator and divide it by 4 to get to 25MHz (or 5 MHz x 5 or whatever) and then low pass filter it. References are typically stable to a few parts per billion, especially if kept indoors and left switched on. As crystal oscillators the phase noise should be excellent.
Old professional test equipment is often a good source of these references, often 5 MHz, 10 MHz or 100MHz. They used to be very common at rallies, but not so much now. Old oscillators are often the most stable due to the ageing characteristics of the crystal.
If you find a 25 MHz reference, Robert's one of your parents siblings. Surplus ovanised 25 MHz references are rare, but for about £20 you can buy a commercial 25 MHz temperature compensated crystal oscillator. For example the D75F-025.0M which is stocked by Digikey, datasheet here: http://www.conwin.com/datasheets/tx/tx237.pdf At 5x7mm it is small enough to fit inside the LNB and has just about acceptable phase noise. It is stable to 0.5 ppm over 0-70C and should be much more stable if kept indoors.
I don't know if anyone has tried the 25MHz reference in those Chinese boards we use in the Portsdown LO.
The QRP labs board mentioned above can also be locked to GPS via the push and pull method using the 1 PPS. This is used in the WSPR beacon for example. I am sure it could be made to output 25 MHz or whatever frequency you need relatively easily but I am not sure about the phase noise.
Square waves are rich in harmonics and most references including the the Leo-Bodnar have harmonics right into the IF region. If you are using two cables then the cross coupling is probably not too bad unless you are using those twin coax satellite TV cables, but when using only one cable like I am, you end up with a marker every 25 MHz. Not usually a problem but it can be if it coincides with the signal you are trying to receive. A low pass filter completely eliminates this.
I have 8 of the Bias-T / Reference boards left, they work fine as long as you order the right parts. My reason for bodges was the boards arrived much sooner than I expected and I hadn't got around to ordering the correct size BNC and I am impatient, so I made another fit. I will ask BATC if they want to do anything with these in the longer term - it is a niche market as I suspect few besides those of us here, are capable of dealing with small SMD parts and doing the necessary surgery to LNBs.
Mike
Firstly, you don't really need to lock to GPS. A very good solution would be to take a good 100MHz ovanised reference oscillator and divide it by 4 to get to 25MHz (or 5 MHz x 5 or whatever) and then low pass filter it. References are typically stable to a few parts per billion, especially if kept indoors and left switched on. As crystal oscillators the phase noise should be excellent.
Old professional test equipment is often a good source of these references, often 5 MHz, 10 MHz or 100MHz. They used to be very common at rallies, but not so much now. Old oscillators are often the most stable due to the ageing characteristics of the crystal.
If you find a 25 MHz reference, Robert's one of your parents siblings. Surplus ovanised 25 MHz references are rare, but for about £20 you can buy a commercial 25 MHz temperature compensated crystal oscillator. For example the D75F-025.0M which is stocked by Digikey, datasheet here: http://www.conwin.com/datasheets/tx/tx237.pdf At 5x7mm it is small enough to fit inside the LNB and has just about acceptable phase noise. It is stable to 0.5 ppm over 0-70C and should be much more stable if kept indoors.
I don't know if anyone has tried the 25MHz reference in those Chinese boards we use in the Portsdown LO.
The QRP labs board mentioned above can also be locked to GPS via the push and pull method using the 1 PPS. This is used in the WSPR beacon for example. I am sure it could be made to output 25 MHz or whatever frequency you need relatively easily but I am not sure about the phase noise.
Square waves are rich in harmonics and most references including the the Leo-Bodnar have harmonics right into the IF region. If you are using two cables then the cross coupling is probably not too bad unless you are using those twin coax satellite TV cables, but when using only one cable like I am, you end up with a marker every 25 MHz. Not usually a problem but it can be if it coincides with the signal you are trying to receive. A low pass filter completely eliminates this.
I have 8 of the Bias-T / Reference boards left, they work fine as long as you order the right parts. My reason for bodges was the boards arrived much sooner than I expected and I hadn't got around to ordering the correct size BNC and I am impatient, so I made another fit. I will ask BATC if they want to do anything with these in the longer term - it is a niche market as I suspect few besides those of us here, are capable of dealing with small SMD parts and doing the necessary surgery to LNBs.
Mike