[Lowfer] OCXO

Wed Mar 12 22:13:08 EDT 2014

Hi All:  Since Garry brought my call sign up the DBM+OCXO approach, I 
noticed that Ridge Equipment still has two more of those IsoTemp 3.000 MHz 
OCXOs
available on e-bay

http://www.ebay.com/itm/Isotemp-Oscillator-3-MHz-905-Model-OCXO127-19-/251008371885?pt=LH_DefaultDomain_0&hash=item3a7143ccad

I have no financial interest or association with Ridge, but have been 
satisfied with the several items purchased perviously over the years.

Info says the heater needs 27V, but I've been running my unit's heater on 24 
volts with no issues.  The oscillator wants 15V and at that B+ level the

second harmonic is -44 down and the third harmonic -58 down tested on my 
HP141T SA.....3.0 fundemental measured +17dBm (4V P-P into 50 ohms)

However, at 12 volts B+ the harmonic levels rose 10 dB or better

Somewhere around 13~14 volts the harmonics settle down to the -44 and -58 
specs.

When I did a cal yesterday the combination of the Isotemp 3.0MHz OCXO and 
the TCXO-9 in my FT-817 was off by only .05 Hz from the previous day.

The heater circuit pulls 300ma or so on startup and settles down around 
70~80ma at 24 volts. Oscillator section pulled around 24 ma at 15 volts....

W9FZ has some data sheets on the Isotemp OCXO.....

http://w9fz.com/ham/sharedrefs.html

24 volt requirement does not bother me, even for field use. My home built 
10GHz xvtr uses both 24 and 12 volt battery power. Two fully charged 12 volt 
batterys

are close to 27.0 to 27.5 and bleed down slowly with the loads I present to 
them....

Plenty of other options out there, this one seemed affordable and worked out 
fine for me. Your mileage could vary, we all have different paths to 
pursue.....

73, Mike wa3tts

----- Original Message ----- 
From: "JD" <listread at lwca.org>
To: "Discussion of the Lowfer (US, European, &amp; UK) and MedFer bands" 
<lowfer at mailman.qth.net>
Sent: Wednesday, March 12, 2014 9:05 PM
Subject: Re: [Lowfer] Audio Noise Floor Measurements on my TS450S

> Many receivers are in exactly the same boat Garry describes.  In my own
> case, it turns out the later specimens of the Kenwood R-5000 are often
> exquisitely sensitive and remain just as clean as necessary down to 30 
> kHz.
> At least, that's true of the 50 ohm input, provided that you furnish it 
> with
> signal from a more or less true 50 ohm source.  (All bets are off with the
> 500 ohm wideband transformer input, which is pretty poor at lower
> frequencies.)  There is no attenuator in line at LF unless you switch one 
> in
> manually.  Only the 0.5-1.6 MHz range is attenuated automatically.
>
> Since I can use SAQ-rx fairly successfully with the spare computer and its
> 48 kHz sound card sampling rate, that means on an ordinary day I only have 
> a
> 6 kHz gap in coverage between 24 and 30 kHz--which, unfortunately, is 
> where
> many of us need coverage right now.  I have one of Todd's modified AMRAD
> converters that does a splendid job but is a little less than convenient 
> in
> the field because it needs 24 volts, and it also magnifies a certain
> shortcoming of the receiver.  I use it for special occasions like SAQ 
> tests.
> My long term solution is probably going to be another upconverter, but 
> this
> time only to 100 or perhaps 200 kHz!
>
> Why not go all the way to 3, 4, or even 10 MHz?  Because the R-5000 
> doesn't
> have enough thermal stability.  With a synthesized receiver, the higher 
> the
> dial frequency, the greater the absolute shift in output frequency for a
> given parts-per-million LO change.  For the temperature variations in my
> field from mid-afternoon to midnight, the receiver I most often use may
> drift 2, 2.5, or even 3 ppm.  If I'm tuned to 3.0295 MHz to copy activity 
> at
> 29.5 kHz, a mere 1 ppm drift over, say, a 2 hour span is going to throw
> things off by a little over 3 Hz...even if the upconverter OCXO stays
> exactly on frequency!
>
> For radios that can be locked to an external reference, that's obviously 
> not
> an issue.  They can benefit greatly from a stable upconverter.
>
> In my own case, though, any lockable LO retrofit doesn't look practical.
> However, I could achieve stability of < 0.13 Hz under the same conditions 
> if
> the radio were tuned to a dial frequency of 129.5 kHz instead.  Not 
> perfect
> for the slowest modes, but a huge improvement!  The radio itself is
> reasonably spur free in the range of 100 to 140 kHz, so _if_ I could keep
> LORAN pulses from sneaking through, and _if_ I can do the frequency 
> division
> from a 10 MHz OCXO without introducing too much jitter (and hence, phase
> noise), then I could fill my coverage gap for little by taking afvantage 
> of
> what the receiver is already capable of doing.
>
> At least, that's the hope.
>
> 73
> John
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