[Premium-Rx] Fw: 1st LO Errors at cold start HF-1000

Sat Feb 14 07:52:49 EST 2015

From: michaelob666 at ntlworld.com 
Sent: Saturday, February 14, 2015 12:46 PM
To: Pat1McA--- via Premium-Rx 
Subject: Re: [Premium-Rx] 1st LO Errors at cold start HF-1000

Good afternoon Jan and the rest of our team

Jan’s receivers, the R1051/URR are described on page 138 of Osterman, Third Edition, and they were build in the period 1960 – 1981.

That’s a hell of a long time ago.

I have four old Racal RA17Ls of the 1960s and none of their 1MHz crystals can be pulled exactly on frequency.  But that’s no problem as it does not affect the correct working of the Wadley Loop.

Most crystal ovens work in the region 60C – 75C.

I wonder whether the crystal has aged so much such that when the frequency error is greatly magnified by the effect of the PLL circuits in the synthesiser of Jan’s radios, phase lock is not achieved until the crystal has warmed up sufficiently to shift the frequency to within the PLL locking region.

On another forum (the WS19 Set lot), an old Racal HF backpack transceiver of the 1970s had a similar problem to Jan’s.  After much discussion between the owner and the wise men on that that forum, the owner obtained a new crystal from the original manufacturer who had supplied Racal back in the 1970s.  Guess what?  After a spot of fine tweaking of the new crystal, the set burst into life.

I similar vein, I recall in the 1980s, my TA military unit took delivery of a new HF system (subsequently called NCRS), put together by Plessey.  At its heart was a very nifty maritime transceiver made by Skanti.  These sets worked extremely well on SSB but were hopeless when in data mode.  I won’t bore everyone with the details but it was a state of the art FEK 4 tone system with highly sophisticated error detection and correction based on the Golay 2 protocol with in-band diversity, error patching, and ARQ when all that lot failed.  

The tecks checked the MO stability of the transceivers with a decent counter but still nothing worked although the FEK tones could be clearly heard.  

I suggested checking the counter’s own MO standard against something better.

Fortunately one of our guys worked for HP and brought along a borrowed HP rubidium standard from his lab.  The Skanti MOs were reset and everything worked flawlessly.

This kit has now been declared surplus and sold off , so no confidentiality issues.

The moral is to check your own frequency source against a seriously good reference.

From: Jan Skirrow 
Sent: Friday, February 13, 2015 2:00 AM
To: michaelob666 at ntlworld.com ; Pat1McA--- via Premium-Rx 
Subject: Re: [Premium-Rx] 1st LO Errors at cold start HF-1000

Hi gang....

Several years ago I bought several R1051/URR radios (1 a B variant, 1 a D and the rest vanilla). For those who don't know this radio it is a modular synthesized comms radio that mostly (I believe) served in naval settings, and the later variants are still apparently in use. The first versions were built with discrete semiconductors and had a couple of tubes in the front end. Over the years they went to more modern integrated circuitry. While in some ways a nice SSB radio, the mechanical bandswitching complexity and general operating kludginess have made them unloved in the collector world!

Anyway the radios use a 5MHz ovenized crystal with a fairly sophisticated temperature control. I have several versions of this module. All are pretty much alike electrically, but some behave very badly. In powering up from cold (room temp - not "frozen North" temp) , the crystal oscillates but is way off frequency - so much so that it seems unlikely that it is operating in the correct mode. The radio itself is non-functional at this point. After some period of time (20 mins or more) the crystal will suddenly snap in to the correct 5MHz and stay there. There is provision for an external 5MHz reference signal, and I expect this was the way these were used in service.

The variants I have seen of the master xtal oscillator all used the same make of crystal, but I wonder if this variety suggests a problem with a particular way of making high precision crystals that was never entirely debugged.

73 de Jan, VE7DJX

On 12/02/2015 3:19 PM, michaelob666 at ntlworld.com wrote:

  -----Original Message----- From: michaelob666 at ntlworld.com 
  Sent: Thursday, February 12, 2015 11:17 PM 
  To: Steve Pappin 
  Subject: Re: [Premium-Rx] 1st LO Errors at cold start HF-1000 

  Dear Steve, 

  This is very interesting.  I must say I was shocked at the behaviour of the 
  WJ receivers that you described. 

  Those of us with Racal kit don't have these problems of master oscillator 
  stability!!!   We have decent crystal standards :-). 

  The Racal-Dana 9442 oscillators in my RA1792 and RA3701 seem to work at all 
  domestic temperatures and after a reasonable warm up will deliver a 
  stability of around 3 parts in 10^9. 

  The 9420 standard in my RA1772 has a spec of 6 parts in 10^10 but of course 
  requires a longer warm up period to reach full stability. 

  For those interested in military radios, the British Army's Clansman VRC321 
  SSB HF tactical transceiver was spec'd over the temperature from -40C to 
  +55C, and the warm up time from -40C was less than 90 seconds.  But then 
  they were a great deal more expensive than an HF-1000!! 

  Presumably all the problems you identified would disappear if one piped in 
  an external 5MHz or 1 MHz reference from an external oscillator of decent 
  stability such as an HP-105 crystal standard or a Rb standard, as one would 
  do at a professional monitoring station. 

  73s 
  Michael 
  G8MOB 

  -----Original Message----- From: Steve Pappin via Premium-Rx 
  Sent: Monday, February 9, 2015 9:33 PM 
  To: premium-rx at mailman.qth.net 
  Subject: [Premium-Rx] 1st LO Errors at cold start HF-1000 

  Why does my HF-1000 display a First LO Error when I start it cold? 

  I'm getting many emails from people with the same error, mostly from the 
  North East and Canada. It's cold temperature related. This usually happens 
  when the radio has been off for a long time and sitting cold. And yes, it 
  happens in the morning 99.9% of the time. The precision reference starts way 
  off frequency because it is not a fully temperature compensated high 
  precision system. It is a TCVCXO. These radios cold soak and can start up 
  weird if they have been sitting. So this is normal behavior for a WJ-8711, 
  8712, or HF-1000 in a colder climate. Since these radios are not MIL spec 
  they will not always start up normally when they are near the edge of their 
  operating temperature range. In fact if you tune side band signals when the 
  radio is cold you will notice how far off the radio is until it completely 
  warms up. Warm up can take anywhere from 15 to 30 minutes. According to WJ 
  radios that have been left turned off for more than 90 days may require 
  adjustment due to crystal relaxation. This is due to the type of component 
  selected, the key word being selected. That is an entire discussion by 
  itself. 

  The reference circuit is made up of the TCVXCXO and supporting components. 
  It receives +5V, +12VA, and is adjusted by a potentiometer. The components 
  are selected for average stability, not extreme stability. The radio is very 
  stable once internal temperatures reach +25C. 

  There was a high stability reference option that is rarely seen (Appendix 
  A). It was created for increased stability over a wide range of conditions. 
  Total reference stability improves from greater than 0.7 ppm to less than 
  0.2 ppm at all temperatures. The -2 RF Tuner Board was installed mainly in 
  the 8711A with the 8 KHz roofing filter and the 8712P. I have never seen it 
  in the HF-1000 and it is rare in the 8712. 

  Best Regards, 
  Steve 

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