Monthly Archives: April 2010

Getting Exactly in Step – Adding a Rubidium Frequency Reference

Based on very helpful information from a forum, the Knowledge Base Article at Flex-Radio’s website and very helpful direct correspondence from Brian Lloyd WB6RQN/J79BP I’ve taken the plunge and have sourced a surplus Datum LPRO Rubidium Frequency Reference from a regular supplier of salvaged and tested LPRO units.

From the Flex-Radio Article (at ):

The Model LPRO-101 makes use of the atomic resonance property of Rubidium (87Rb) to control the frequency of an unheated quartz crystal oscillator via a frequency-locked loop (FLL). All commercial rubidium frequency standards operate by disciplining a crystal oscillator to the hyperfine transition at 6.834,682,612 GHz in rubidium. The amount of light from a rubidium discharge lamp that reaches a photo detector through a resonance cell will drop by about 0.1 % when the rubidium vapor in the resonance cell is exposed to microwave power near the transition frequency. The crystal oscillator is stabilized to the rubidium transition by detecting the light dip while sweeping an RF frequency synthesizer (referenced to the crystal) through the transition frequency.

The Efratom LPRO-101 is a Rb oscillator that can used to discipline the FLEX-5000 and FLEX-1500……

I’ve the appropriate header to use as a plug, a BNC Terminated Cable to carry the signal to the Flex-5000A, a suitable power supply and a very different disconnect plug (as I do not have 20V DC in use for anything else). I thought I had appropriate heatsinks in my parts box, but they must have been used for something else. So I will need to fabricate a heat dissipation plate before putting the Rb Frequency Reference in continuous use.

As a “step-two” the circuit to indicate the status of the unit “lock” will be added.

Here are some references on this:

I need to tip my hat to the folks at AR15.Com’s Amateur Radio Forum who pointed me to Time-Nuts at which proved to be phenomenally interesting and helpful.

Photos and use-report to follow once I have everything running to satisfaction.



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Satellite Antenna Project – Next Step

With the Diplexers and Wiring Harnesses completed, it is time to do the easy part – the physical antennas. (for the Diplexer & Harness Build see  Building Microdiplexers with Victor KC9NWB )

Looking locally for the 1/8″ diameter common brass rod VE2ZAZ designed his antenna version around neither the quantity nor price-point were very attractive.  Little short pieces and expensive.

Found that McMaster-Carr has the rods at a very good price in 6 ft lengths.  They must have a special deal with their shippers as the shipping charge was very modest as well.  I also bought the CPVC tube and Vinyl End Caps from them, to top up my order above minimums and for ease of shopping.  Those prices were also very very good, though I don’t know what I am goingto do with all the extra vinyl end caps, given that the minimum order quantity was 100 pieces!

Did find that my circuit boards are a hair oversized, and I will need to make a decision whether to go to a larger boom or if I am going to add a “Diplexer Pod” externally.  I am leaning to the Pod and exterior wiring, with the idea of using the Pod as a future attach point for a receive preamp.

Mechanically I am looking at ways to make the elements easy to remove and reinstall.  Thinking of trying a couple ideas with scrap materials before drilling the booms.

Thinking of using an epoxy putty ball  with a small plastic cross-pin through it applied to each element on one side of the boom and then using elastic rubber bands to hold the elements in place when assembled.  Would provide for positive indexing and I could use letter stamps to mark each element for location.  Have a couple other ideas with heatshrink tubing and a clip.

Pictures soon!



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Building Microdiplexers with Victor KC9NWB

With my youngest son Victor KC9NWB I’ve started a Father-Son project to build a Satellite/ISS Antenna and do some contacts.

Rather than buying everything in, we decided to build, and here are some shots of building the Diplexer (I’d been corrected that these are Diplexers to hook two antennas to one radio, rather than Duplexers.)

We’re building a small batch, with two destine for friends.

My workspace was improvised to get the best of natural light and interior lighting.

My Workspace for the Project

I taped a third-hand onto my Panavise and had sourced the very small tools from internet providers.

Teflon Circuit Boards came from Far Circuits and the SMT components came from DigiKey.

Here is the batch of boards being final checked.

Everything was so very small.

Notice the Penny for Scale and the Very Fine Soldering Tip

One of the inductors – a 15nH thing, wasn’t available in the designed package and I got talked into using a smaller one yet! This was a special challenge and the tolerance for installation was basically “nil.”

I think you could breath these little inductors in if you weren’t careful!!!!

Lost one at one point (I was warned and bought extras of everything) and couldn’t find it. Middle son Winston KC9FVR could see it on the hardwood.

When you look under magnification you can see the little coil in it – simply how do they do that!!???

Completed Diplexer Boards with their Coax Cable Harnesses

Next project weekend we will do the mechanical part.

Here are project links:

More as our project progresses!



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Small Wonder Labs Retro-75 Kit Arrives and Project Start

The Retro-75 Board Kit has arrived this week. It came in two parts, everything but one component which arrived separately a few days latter (there was a note in the first package).

I’ve a satellite antenna project with my son Victor KC9NWB and a frequency reference for my shack to finish, both “on the bench” to complete first, putting the Retro-75 into a May build.

That will give me time to layout & source an enclosure, the second crystal socket & switch I will install and have those items on hand for the build.

My initial post on the Retro-75 is at: Going Retro on 75m AM – Small Wonder Labs Kit

I’m planning to shoot pictures and write something about all three projects as they go along.



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An Excellent Write Up on Coax, Types, Brands, Un-Branded Cable and use of Stubbs

James Brown K9YC has released an update of his coax notes (James K9YC QRZ Page is at )

Most of what it says seem to match with reference material and the reference books.

In PDF form you can download his ten-page “white paper” at this link:



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A Free eBook on Radio Monitoring

This appeared in the recent NAQCC Newsletter and may interest some of us:

From Skip N2EI NAQCC #3317 –
Many of you know that, some time back, I authored a book called “Radio Monitoring – A How To Guide”.

Originally published by Index Publishing Group and later released by Paladin Press, is had two very successful editions that sold for many years.

This book has recently gone out of print but I am pleased to say that I have now released it on line (for FREE) via Creative Commons license.

I admit that a few points are a bit dated but the book still has a lot to offer the beginner or even experienced radio hobbyist.

You can download a copy thanks to the North American Shortwave Association (NASWA) who have consented to be the primary online source for distribution.

The direct link is here – .

The hobby has been good to me over the years.

I am happy to give this book back to the radio community. Enjoy. [Skip N2EI]



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