[time-nuts] New Member + Basic Questions

Rob Sherwood. rob at nc0b.com
Sun Jan 10 15:35:58 EST 2016

Hi Nathan,

I have had all three types of house standards over time.  For decades I used Sulzer 2.5 and 5.0 MHz standards for my ham shack / lab. See link.  


Of course there are much more modern and small units today, but it was a exciting to track them against WWVB back in the 1970s and 1980s.  You never wanted them to lose power, or it took weeks for them to settle down again. 

Many of my HP pieces of test equipment have HP 10811 OCXO units in them.  They are very good, even if old, assuming the oven is working correctly.  I think any piece of HP equipment with a 10811 in it will also lock to an external standard.  This is good because it is really touchy to try to set a 10811 right on frequency. (I am assuming you are trying to set it within 1x10^-8 or better.)  

In the mid to late 1990s I bought a NOS Efratom M-100 Rubidium. I wish I knew the date.  See link.

It has been in operation 24/7 ever since then, and it has very good phase noise and has been within 1x10^-10 all these years.  Who knows why it has been so stable. It has been so good I purchased a Lucent / Efratom Rubidium for my other QTH / Lab. It also is within 10^-10, though I don't run it 24/7.  It takes about 5 minutes to warm up, though it is more stable after an hour if we are really picking nits.  

I have a GPSDO at both locations to check on the accuracy of the Rubidium oscillators periodically.  The phase noise of the Rubidium oscillators and my Trak GPSDO are better than -130 dBc @ 1 kHz offset.  Assuming accuracy of around 1 part in 10^-10 is more than adequate for a house standard, you cannot go wrong with a good Rubidium.

Your first example of a GPSDO on eBay is available from RDR Electronics. You cannot go wrong with them. Skip is an expert on time and frequency equipment, and the company stands behind their sales.  They happen to be in Denver, and I have been to their store many times.  I know nothing about your second option, but those units are on eBay all the time. Considering the support you can get from RDR Electronics, I would go with that if you want a GPSDO. They have Rubidium oscillators, too. 

An HP 8640A or B will not lock to a standard, as the basic oscillator is a cavity. The 8640B can stabilized to its counter, but keeping 8640s working, and not having cracked gears is a challenge. I never heard of an 8650. You might consider an 8657B for a generator. For a counter consider an HP 5335A.  If you need 11 digits, then an HP 5345A is good, but very large and complicated. (I have both.) 

You will need a distribution amplifier for your house standard if you are going to run a lot of equipment off of it (say 6 or more). Otherwise a Mini-Circuits hybrid splitter will work.  (2 way, 3 way or 4 way) I use a 4-way splitter off the Lucent for two 8642A generators and two 3336C generators.  It just depends on the output level of the house standard and how much signal a given piece of equipment needs to lock. An 8657B will likely be good enough as to phase noise for general usage.  If you are trying to test state-of-the-art radios like I do, then there is no affordable used HP generator good enough except the HP 8642A.  Even the 8662A isn't low enough in phase noise to test the absolute top low-phase noise amateur transceivers on the market today. (Flex 6000, Apache ANAN 200, Elecraft K3S or KX3) Keeping 8662A or 8642A synthesizers working is not a piece of cake, so I would stay away from them unless you really need low phase noise generators.  

Good luck, and welcome to the hobby. I got my general in 1961, and it has been a wonderful experience.

73, Rob Sherwood, NC0B 


-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Nathan Johnson
Sent: Sunday, January 10, 2016 11:26 AM
To: time-nuts at febo.com
Subject: [time-nuts] New Member + Basic Questions

Hello All,
I'm a ham radio operator, for just a few years, and electronics nut for many more. I have been reading the archives and trying to learn a bit. I am wanting to develop an accurate frequency standard for "lab" and radio use. I see that I have 3 basic options that are possible on my budget, a decent OCXO-based device, a rubidium standard, and a GPSDO. My current uses are to supply accurate timing to a signal generator(not yet purchased, HP 8640/8650-something) and a frequency counter(Fluke 1953), mostly used in aligning radios.
In the near future I am hoping to expand that to a homebrew HF transceiver(probably clocking a DDS chip of some sort), and some higher frequency(possibly up to 10GHz) transverters.
So what I have learned so far about each option:
-OCXO is probably stable enough for what I am trying to do, but by itself provides no guarantee of absolute accuracy(I'm looking at the microwave operators "weapon of choice", the Isotemp 134-10), has an adjustment pin for a tuning voltage, but no idea what an appropriate value is for that voltage without access to a more accurate standard. I will probably build an OCXO device of some kind anyway as an interim measure while I earn for the money to obtain something better, and to validate a distribution amp within the lab etc.
-Rubidium Standard seems like a very nice idea, but it's still not traceable in terms of absolute accuracy(although the adjustment range of the available standards appears to be several orders of magnitude better than I am likely to need). The available standards are being re-imported from China, with unknown hours or life remaining, and in some cases unknown condition. They appear to be power hogs. A $200 gamble.
-GPSDOs have many options available, and are referenced to primary standards.
Pretty sure this is where I want to go. I'm looking at Item# 231803015799 on the usual auction site, and this seems to be everything I need? I also looked at item# 111514491254, but there doesn't seem to be any documentation about what's inside.
Am I missing key points here? Or am I headed on the right path? Appriciate any and all input.
Nathan KK4REY

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