Re: Chineses TCXO for 28 MHz IF 2M transverters


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

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