Regular reports of my grabber activity and that of others, plus information on QRSS software, hardware and technique that comes my way

Monday, April 18, 2011

Temperature Control for My Kenwood TS-440

Here's how to add a temperature controller to an older rig like my Kenwood TS-440.  Essentially you just make a copper sleeve for the master crystal, glue on a pair of heating resistors, a LM-35 temperature sensor and use a 4-wire cable to connect to the control circuit located outside the rig.  This is the same approach I described previously in Part 1 of my series on temperature controllers.

The main requirement it that the frequency of the receiver be controlled by a single master crystal as in the TS-440.  Older radios with multiple crystals used for the various hetrodyning stages will be too awkward to adapt because a separate controller would be required for each one.*

The TS-440 is actually pretty challenging with respect to cramped quarters.  The crystal is located in the middle deck of a stack of 3 PC boards with very little room for the compact sleeve that fits around the xtal....but it just works.  Figure 1 shows what we're up against.

Figure 1.  Location of master crystal in the TS-440

The front of the rig is at the top of the photograph.  Note the upper deck has been swung up to allow access to the middle deck where the crystal is located.  The small chassis to the right contains he outboard temperature control circuitry.  The cable connecting the two is a 4-conductor type from an old modem line.

Figure 2.  Close-up of Copper Sleeve Installed on Crystal

Figure 2 is a closer view of the crystal location showing the copper sleeve installed.  The heating resistors are on the left and right sides of the sleeve and if you look carefully you can see the TO-92 case of the LM35 in between.  Note how close the crystal is to the shield of one of the PLL's...there is only a few mm spacing and no room for Styrofoam insulation as I have used with other TC's.

Figure 3.  Case Closed

Figure 3 shows the case closed back up.  Along the front of the controller are, L to R, temperature control pot, LED indicator, Temp or drive voltage switch and RCA plug for voltmeter.  Figure 4 shows everything set up and operating.  When power is first applied to the controller the LED glows brightly then gradually dims to a steady value to indicate regulation.

Figure 4.  System in Operation

How does it perform?  Bottom line, the frequency is stable enough for long duration stacking work up to 6 hours.  When I monitor WWV the variation over a day is +/- 1 Hz when the wx is nice enough to leave the windows open 24/7 and outdoor temperatures vary by 15 degrees F.  I adjusted the operating temperature to 125 deg F (52 C) which is the measured turn-around point for the TS-440 crystal.  I determined this by varying the temperature with the pot and noting the point where temperature quits decreasing and starts increasing again....see Part 1.  The ceiling fan has a noticeable effect on temperature variations and when I'm really serious about stacking I leave it on low speed to keep the air in the shack well stirred.

de w4hbk

Friday, April 15, 2011

WA5DJJ's new mept

Dave, WA5DJJ, has brought together some ideas to produce the ultimate QRP Labs mept modification that is stable in both time and frequency to make it adequate for image stacking.  To jog ur memories, it is possible to stack successive grabs using an astrophotography program called Rot'N'Stack to pull really weak signals out of the noise. To do so the message must appear at exactly the same place on the grab from one to the next, i.e., must be stable in both time and frequency. The SNR improves as the square root of the number of images stacked.  I'll leave it to Dave to describe his mods but basically it involves using the 4-component temperature controller I described in Part 2 of my series here on this blog and the change to a PIC keyer designed by Mike, N0QBH.  This latter mod allows a 32 kHz clock xtal to stabilize the timebase.

Last night I recorded the signal from Dave' new rig and the results were nothing short of phenomenal.  Over a period of 4 hours he drifted only 1 Hz, which as I told him could easily be my rx...the wx is wonderful now and we're leaving the windows open in the shack resulting large temperature changes.  The times base was virtually jitter free and started exactly on time every 10 minutes.  Figure 1 shows his signal as recorded on my 5 hr grabber. 

Figure 1.  5 hour grabber showing Dave's signal

Each of the short pulses represents a 10 minute grab as normally seen on my regular grabber.  I used 25 of the 10 minute grabs, going from 0717z to 1114z, in the Rot'n'Stack stacking program to produce the averaged image shown in Figure 2.  Even though Dave's signal was strong and didn't need stacking to bring it out of the noise, this provided an acid test of his rig's stability in both time and frequency.  The degree to which it is off will appear as blurring or jitter.  The timing is virtually perfect and what little frequency blur there is is caused by the 1 Hz drift over the recording time.

Figure 2.  Stacked average of 25 grabs

In addition to Dave's signal, several surprises popped out of the noise.  VK6JY is using a stabilized Hewlett-Packard signal generator which responded quite well to the stacking process.  There was no hint of N4FRE or ZL1EE even on the 5 hr grab which has a much better SNR than the 10 minute grabbs.  Both have highly stabilized signals via atomic clocks and/or GPS.  FRE usually drops completely out this time of night and if any of his signal was left it was completely obliterated by P29ZL.  It's ironic to be using sophisticated software and equipment to extract a 'local' station out from under one so far away (with an antenna  up in a banana tree no less).  However ZL's mept is not stabilized in time and thus averages at the same time FRE's builds up.  QRSS does have it's moments.

Congratulations to Dave on his new rig.  It looks like all the mods can be added directly to the rig so it will still fit in an Altoids tin.  Now if everybody adopts those mods then they too can pop out of the noise when stacking is applied.

de w4hbk


The signal of P29ZL caught my attention soon after it's appearance on my grabber last month for two reasons.  First, it appears almost every night for about 5 hours, very strong and easy to copy.  But equally interesting is the extreme multipath/Doppler effect which is always present for at least part of the time.  Tim's mept, from the WA5DJJ Labs,  runs 250 mW to an inverted V hung in a 25 foot banana tree.  Figure 1 is a 5 hour grab from a few nights ago and is typical of what I see every night:  note in particular the considerable fuzziness of the signal between 1000 to 1100z.  Figure 2 is from the 10 minute grabber and shows the effect in more detail.  Other signals from out that way, most notably VK6JY show just a bit of broadening but nothing like that from P29ZL.

Figure 1 - P29ZL on the W4HBK 5 hr grabber, 12Apr11, 30m 

Here is my understanding of the multipath/Doppler effect.  As the signal passes through the ionosphere it may be partially refracted back towards Earth but a part may continue on to find another refracting region for a second signal, an so on.  At the same time multiple hops can occur with the results that a number of signals can arrive at the receiving antenna.  But for a Doppler shift to occur these various regions must be moving relative to one another.  Without this relative motion the signals arriving from the various paths would be at the same frequency but differing in phase to cause fading due to interference.  Other phenomena such as ionospheric irregularities and turbulence can also contribute a continuous broadening....visualize an eddy where some of the electrons are moving towards and some away from the path of propagation.  I've noticed that most writers of the scholarly articles end up stating how complex is the the kid next door says to me sometimes. "Well, Duhhh!"

Usually the M/D effect is relatively simple with just 2 noticeable frequencies and I see this almost every day on one signal or another as the band is changing around sunrise/sunset.  What makes the fuzz on P29ZL's signal unique is that it's a daily occurrence with a near-continuous broadening, usually towards a higher frequency which would indicate the path length is decreasing.  Sometimes one or two distinct frequencies appear out of the continuum.

Enough for now about this most interesting signal but I will be keeping an eye on things and doing a bit more reading.

de w4hbk