Chineses TCXO for 28 MHz IF 2M transverters


Keith Morehouse
 

I don't know how good these are or what the ultimate output level is, but this is the frequency you need if you want to stabilize your older DEMI (or whoever) 144 MHz transverter.  They are being sold by the pair, so you have one to break and one to use.  They shouldn't be too hard to integrate into almost any 28 MHz IF transverter.  Look up the specs of your mixer for LO power requirements, check this one and then either pad it down or, more likely use it as is or drop a 0.99$ MMIC in as a buffer amp. I am sucked in for a pair.

I've had a EBay search active for this frequency TCXO for two years and this is the first usable (hopefully) unit that has come up.  I messaged the seller to make SURE it was a sine-wave output (most of these are clock oscillators with TTL or CMOS square-wave's output) and he verified it was sine-wave.  If not, I guess I could legit return it by showing EBay his message.

I bought a TCXO advertised just like this as a drop-in for a Yaesu FT817 and it worked fine and was dead on freq, out of the package.  It was 20% the cost of a Yaesu equiv part.


-W9RM

Keith J Morehouse
Managing Partner
Calmesa Partners G.P.
Olathe, CO


John Klem
 

I have been interested in similar low-cost TXCOs, but concerned about what's in the package.  It would be very interesting to see an output spectrum. 

Given that you are probably driving a mixer that is basically a diode switch, it's not clear to me that a square wave would be a problem.  Even with a sine wave LO, you are creating mixing products around multiples of the LO frequency, and any decent amount of filtering downstream of your mixer takes care of that problem.  Does anyone know more about this topic?  I have considered a 222 transverter LO using a MEMS oscillator chip (square-wave output), and was thinking that LO filtering would not be necessary.

John, AA5PR

On 12/8/2018 9:22 AM, Keith Morehouse wrote:
I don't know how good these are or what the ultimate output level is, but this is the frequency you need if you want to stabilize your older DEMI (or whoever) 144 MHz transverter.  They are being sold by the pair, so you have one to break and one to use.  They shouldn't be too hard to integrate into almost any 28 MHz IF transverter.  Look up the specs of your mixer for LO power requirements, check this one and then either pad it down or, more likely use it as is or drop a 0.99$ MMIC in as a buffer amp. I am sucked in for a pair.

I've had a EBay search active for this frequency TCXO for two years and this is the first usable (hopefully) unit that has come up.  I messaged the seller to make SURE it was a sine-wave output (most of these are clock oscillators with TTL or CMOS square-wave's output) and he verified it was sine-wave.  If not, I guess I could legit return it by showing EBay his message.

I bought a TCXO advertised just like this as a drop-in for a Yaesu FT817 and it worked fine and was dead on freq, out of the package.  It was 20% the cost of a Yaesu equiv part.


-W9RM

Keith J Morehouse
Managing Partner
Calmesa Partners G.P.
Olathe, CO


Robin Midgett <K4IDC@...>
 

Alternatively, use a LPF such as these from QRPLabs to derive the sine from the square wave. I did that for the Si570 synthesizer output to drive an old GE MASTRII transmitter chain to make a 6m beacon; works great.
Thanks,
Robin Midgett K4IDC


On Sat, Dec 8, 2018 at 6:11 PM John Klem <klemjf@...> wrote:

I have been interested in similar low-cost TXCOs, but concerned about what's in the package.  It would be very interesting to see an output spectrum. 

Given that you are probably driving a mixer that is basically a diode switch, it's not clear to me that a square wave would be a problem.  Even with a sine wave LO, you are creating mixing products around multiples of the LO frequency, and any decent amount of filtering downstream of your mixer takes care of that problem.  Does anyone know more about this topic?  I have considered a 222 transverter LO using a MEMS oscillator chip (square-wave output), and was thinking that LO filtering would not be necessary.

John, AA5PR

On 12/8/2018 9:22 AM, Keith Morehouse wrote:
I don't know how good these are or what the ultimate output level is, but this is the frequency you need if you want to stabilize your older DEMI (or whoever) 144 MHz transverter.  They are being sold by the pair, so you have one to break and one to use.  They shouldn't be too hard to integrate into almost any 28 MHz IF transverter.  Look up the specs of your mixer for LO power requirements, check this one and then either pad it down or, more likely use it as is or drop a 0.99$ MMIC in as a buffer amp. I am sucked in for a pair.

I've had a EBay search active for this frequency TCXO for two years and this is the first usable (hopefully) unit that has come up.  I messaged the seller to make SURE it was a sine-wave output (most of these are clock oscillators with TTL or CMOS square-wave's output) and he verified it was sine-wave.  If not, I guess I could legit return it by showing EBay his message.

I bought a TCXO advertised just like this as a drop-in for a Yaesu FT817 and it worked fine and was dead on freq, out of the package.  It was 20% the cost of a Yaesu equiv part.


-W9RM

Keith J Morehouse
Managing Partner
Calmesa Partners G.P.
Olathe, CO


Bill
 

Hi Keith,

One thing about ref oscillators:  I use 5 volt dc powered oscillators especially portable ops. They need a regulated and filtered supply so one must have adequate headroom for the regulator. 10 or 12 vdc oscillators won’t get it done.  OK for home use. 

I’ve used several CTI-196 units but they’re pretty expensive now at abt $30 each. They do sine outputs at 10 ^-5. Good enuf for 10 and 24. Pyrojoseph still has them on ebay. 

Looking for smaller units a little smaller than a postage stamp. Need to be 5v, sine out at 2-3 volts pp 10 MHz.

73 Bill W7QQ 


On Dec 8, 2018, at 9:22 AM, Keith Morehouse <w9rm@...> wrote:

I don't know how good these are or what the ultimate output level is, but this is the frequency you need if you want to stabilize your older DEMI (or whoever) 144 MHz transverter.  They are being sold by the pair, so you have one to break and one to use.  They shouldn't be too hard to integrate into almost any 28 MHz IF transverter.  Look up the specs of your mixer for LO power requirements, check this one and then either pad it down or, more likely use it as is or drop a 0.99$ MMIC in as a buffer amp. I am sucked in for a pair.

I've had a EBay search active for this frequency TCXO for two years and this is the first usable (hopefully) unit that has come up.  I messaged the seller to make SURE it was a sine-wave output (most of these are clock oscillators with TTL or CMOS square-wave's output) and he verified it was sine-wave.  If not, I guess I could legit return it by showing EBay his message.

I bought a TCXO advertised just like this as a drop-in for a Yaesu FT817 and it worked fine and was dead on freq, out of the package.  It was 20% the cost of a Yaesu equiv part.


-W9RM

Keith J Morehouse
Managing Partner
Calmesa Partners G.P.
Olathe, CO


John Klem
 

Someone has already done spectral testing of similar units (link below).  It's a long read, but the bottom line is that at least some of these are very likely to be (cheap!) synthesizers, with spurs and higher phase noise than you will find in a good TXCO.  The article documents degraded receiver performance. 

At least those of us in "rich" RF environments might be better off avoiding them.  On the transmit side, it might also be kinder to our nearby amateur friends.  Still, in some cases (like Keith's transverter LO) there may not be better options.

https://sites.google.com/site/markstcxomeasurements

John, AA5PR

On 12/8/2018 9:22 AM, Keith Morehouse wrote:
I don't know how good these are or what the ultimate output level is, but this is the frequency you need if you want to stabilize your older DEMI (or whoever) 144 MHz transverter.  They are being sold by the pair, so you have one to break and one to use.  They shouldn't be too hard to integrate into almost any 28 MHz IF transverter.  Look up the specs of your mixer for LO power requirements, check this one and then either pad it down or, more likely use it as is or drop a 0.99$ MMIC in as a buffer amp. I am sucked in for a pair.

I've had a EBay search active for this frequency TCXO for two years and this is the first usable (hopefully) unit that has come up.  I messaged the seller to make SURE it was a sine-wave output (most of these are clock oscillators with TTL or CMOS square-wave's output) and he verified it was sine-wave.  If not, I guess I could legit return it by showing EBay his message.

I bought a TCXO advertised just like this as a drop-in for a Yaesu FT817 and it worked fine and was dead on freq, out of the package.  It was 20% the cost of a Yaesu equiv part.


-W9RM

Keith J Morehouse
Managing Partner
Calmesa Partners G.P.
Olathe, CO


Keith Morehouse
 

John, thanks for digging up that info.

I did buy a couple and they were certainly cheap enough to just throw away if they don't perform.  I don't have a phase-noise test setup and I understand that this is one of the more important specs in any oscillator.  But, I do have a real spectrum analyzer and will do a critical evaluation of them, at least as much as I can.  If anybody out there does have a phase-noise measurement box, I'd be happy to send one of these.

The cheap Chinese unit I bought for the FT-817 was evaluated for phase-noise (not by me) and found to be "pretty good" for the price - as good as the stock Yaesu (which isn't that great).  Unfortunately, a large percentage of amateur radio gear isn't stellar as far as phase-noise is concerned.  Since this is for 144 MHz, a band where I have no other local stations, a little bit of ragged extra bandwidth isn't really a show stopper.  I'll throw it in the same category as the nasty APRS beacon here in the valley that lights up a significant amount of spectrum every time it does it's thing.

-W9RM

Keith J Morehouse
Managing Partner
Calmesa Partners G.P.
Olathe, CO


On Mon, Dec 10, 2018 at 9:40 PM John Klem <klemjf@...> wrote:

Someone has already done spectral testing of similar units (link below).  It's a long read, but the bottom line is that at least some of these are very likely to be (cheap!) synthesizers, with spurs and higher phase noise than you will find in a good TXCO.  The article documents degraded receiver performance. 

At least those of us in "rich" RF environments might be better off avoiding them.  On the transmit side, it might also be kinder to our nearby amateur friends.  Still, in some cases (like Keith's transverter LO) there may not be better options.

https://sites.google.com/site/markstcxomeasurements

John, AA5PR

On 12/8/2018 9:22 AM, Keith Morehouse wrote:
I don't know how good these are or what the ultimate output level is, but this is the frequency you need if you want to stabilize your older DEMI (or whoever) 144 MHz transverter.  They are being sold by the pair, so you have one to break and one to use.  They shouldn't be too hard to integrate into almost any 28 MHz IF transverter.  Look up the specs of your mixer for LO power requirements, check this one and then either pad it down or, more likely use it as is or drop a 0.99$ MMIC in as a buffer amp. I am sucked in for a pair.

I've had a EBay search active for this frequency TCXO for two years and this is the first usable (hopefully) unit that has come up.  I messaged the seller to make SURE it was a sine-wave output (most of these are clock oscillators with TTL or CMOS square-wave's output) and he verified it was sine-wave.  If not, I guess I could legit return it by showing EBay his message.

I bought a TCXO advertised just like this as a drop-in for a Yaesu FT817 and it worked fine and was dead on freq, out of the package.  It was 20% the cost of a Yaesu equiv part.


-W9RM

Keith J Morehouse
Managing Partner
Calmesa Partners G.P.
Olathe, CO