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

[michaelob666 at ntlworld.com]

-----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


---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com

______________________________________________________________
Premium-Rx mailing list
Home: http://mailman.qth.net/mailman/listinfo/premium-rx
Help Page: http://mailman.qth.net/mmfaq.htm
Post: mailto:Premium-Rx at mailman.qth.net
Help Contact eMail:  paul at 8zo.com
Home Page:  http://www.premium-rx.org/