A 40 Meter LPF for the Pixie

Posted on February 20, 2017 by robert

As I mentioned the 40-meter Pixie QRP rig has pretty horrible harmonics, well above the maximum allowable FCC limit (-43 dBc).  One Pixie was about -9 dBc, and the other was about -20 dBc.

The output filter in the Pixie is a simple 3-pole PI network, clearly not up to snuff.  With judicial parts placement, an extra 5-pole filter could be installed, but it probably makes sense to install it in an external box (Like a Pomona 3231 or 2391).

Several club members and I embarked on experiments to build a prototype filter, with some different choices of -3 dB cutoff frequency, output ripple, etc.  We also discovered that while many of the online calculators produced very similar results, at least one of them does not.  Filters built using those values did not match up well with predicted results.

John King, WA1ABI, suggested using “Elsie” from Tonne Software.  Far more flexible than the online calculators, it produced output values that were consistent as long as the initial parameters were correctly selected.  The software can be downloaded here:

http://www.tonnesoftware.com/elsiedownload.html

I used an online calculator that produced identical results to Elsie:

http://www.calculatoredge.com/electronics/ch%20pi%20low%20pass.htm

Input values were a cutoff frequency of 7.5 MHz, 50 Ohm impedance, 1 dB ripple, and a 5-pole Chebyshev filter.  That produced the C1/C2/C3 & L1/L2 values shown below:

 

C1 & C3 were fabricated from a 680 pF in parallel with a 220 pF, for a total of 900 pF (less than 1% low).

C2 was fabricated from three caps in parallel; 470 pF, 470 pF, and 330 pF, for a total of 1270 pF (less than 1% low).

 

My inductor was set to 1.2 uH, about 4% high, but that required 20 turns on a #6 core.

I had chosen T37 cores for their small size and had initially planned on winding them with #26 wire.  However I switched to #20 for mechanical reasons.  A T37 core can hold about 13 turns of #20 in a single layer, and 20 turns of #20 in a dual layer — perfect.  14″ of #20 magnet wire was enough to wind 20 turns with 1.5″ long pigtails.  It was tight, but things fit.


The final breadboard circuit looked like this:

 

The test setup looked like this, with the breadboard hooked up in series between the Tracking Generator output and Spectrum Analyzer input:

 

The measured response was:

  • 7.055 MHz -2.6 dB (Operating Frequency — loss is higher than expected)
  • 7.429 MHz -3.0 dB (Cutoff Frequency — a bit lower than expected)
  • 14.112 MHz -35.1 dB (2nd Harmonic)
  • 21.168 MHz -29.7 dB (3rd Harmonic)

 

Posted in Gear, Pixie, Projects, QRP | 2 Comments

Pixie Varibility

Posted on February 16, 2017 by robert

Given the dismal harmonic supression of my first Pixie kit, I was excited to test another. While still not passing, it is isn’t absolutely dismal.

The readings were taken with a 40 dB external attenuator.  So the fundamental is actually +25.1 dBm (or 320 mW).  The 2nd harmonic is at +3.5 dBm (2.2 mW).  This is is a reduction of 21.6 dB, still not meeting the 43 dB specification, but better than the first unit I tested, which only reduced the 2nd harmonic by 10.1 dB.

So why the difference?  Could be component variation.  Could be an assembly error.

Posted in Pixie, Projects, QRP | Leave a comment

QRP Still Rules the World; even on 80 Meters

Posted on February 13, 2017 by robert

Yesterday I decided to set my radio up on a QRP (5 watt) beacon mode on 80 meters (I used a propagation mode called WSPR, transmitting once every 10 minutes).  I let the rig run from about 4:45 PM local time yesterday to 11:00 AM this morning.  In that time, as you will see from the map, I was copied pretty much everywhere in the US and Europe.  I also made it around the globe to Tasmania (that yellow colored line heading off the bottom left corner).

Pretty much proves that QRP can work the world, even on a band like 80 meters, not usually the #1 choice for DX.

Posted in DX, Propagation, QRP | Leave a comment

Pixie Pain

Posted on February 11, 2017 by robert

There is an inexpensive QRP kit that sells on eBay for somewhere between $4-10, called a Pixie.  It is a single conversion rock bound 40 meter QRP rig often set to 7.023 MHz, but sometimes 7.040 MHz.  They are often described as a 1 or 2 watt rig.  I decided to purchase one to see how well it performs.

In various tests, I did manage to blow out the 8050 final amplifier device, and I can tell you running it at 13.8 volts is probably a big mistake as it leaves that device dissipating about 2 watts — far beyond its rating.  On the other hand, 10.4 volts (which puts the internal power rail at about 9 volts) is probably a bit on the low side.  My unit does not pass FCC emissions requirements (spurious emissions must be -43 dBc).  And being Direct Conversion, a lot of power leaks out the antenna on transmit.

The setup is as follows:
  • Pixie is driven with a 10.4 VDC power supply (and consumes 10 mA in receive and 60 mA in transmit)
  • Output power measured with a QRP watt meter is 140 mW at 10.4 VDC input.
  • Pixie is terminated with a 50 ohm dummy load.
  • The Oscilloscope is in parallel with the dummy load (1x probe setting)
  • The Spectrum Analyzer is fed with a 40 dB external attenuator.
Let’s begin with the RX scope photo, which shows 112 mVrms (calculated by the scope) and 332 mVpp.  At 50 ohms that is 0.25 mW, or -6 dBm:
Inline image 1
Moving on to the TX photograph, which shows 7.04 V p-p, which is 2.49 Vrms.  which is 125 mW, or 21.0 dBm:
Inline image 2
Moving to the frequency domain — (add +40 to all values due to external attenuator).  The fundamental on receive is leaking through at -6.38 dBm, which is .23 mW.  Adding in the second and third harmonics gets us to .25 mW, exactly what we see on the O-scope:
Inline image 4
On TX we have the fundamental at +19.7 dBm (94 mW).  The second harmonic is 9.58 dBm (9.1 mW).  The third harmonic is -8.17 dBc (0.2 mW).  That’s a total of 103 mW, a bit lower than the scope reading of 125 mW:
Inline image 3
Posted in Gear, Pixie, QRP | 1 Comment

HELP: My TH-D74A Radio Won’t Go into DV Mode

Posted on February 4, 2017 by robert

Well, not MY TH-D74A, but that was a problem a friend was having with his new Kenwood TH-D74A radio.  He could NOT select a memory channel programmed to DSTAR (Kenwood calls that DV for Digital Voice, or DR for Digital Repeater).  Also he could not use the “MODE” button (one of the buttons on the keypad) to select DV.  It would cycle through FM, AM, USB, LSB, CW, and back to FM).

Calls to Kenwood were not productive:  “If you press the MODE button it will allow you to select DV”, followed by “No I know of no reason why DV isn’t showing up as a choice on your radio.  It has to be there.”  And the Yahoo group was full of good suggestions, but none of them fixed the issue.

My friend knew it COULD work, because it did work briefly — he was able to select MODE DV, or pick a DSTAR memory channel, but that happened after hours (and I mean like 12 solid hours) of “lets try this” button pushing.

It isn’t my radio, so that made life quite difficult, and it’s a long drive to his house and back.  I finally downloaded the manual and read the DSTAR and Memory Channel sections of the book from end-to-end and there was absolutely NOTHING in there to describe the problem.  So I read the entire manual (did I mention it was for a radio I do NOT own?  How many people read the manual for radios they DO own?).  Finally I found three little notes at the end of a unrelated chapter.  One of them said “The radio may be in DV Mode in Band A or Band B but not both”.

Like many radios, the TH-D74A can be configured to monitor two frequencies at the same time.  These two monitored frequencies, for reasons beyond my understanding, are called “BANDS” — Band A, and Band B.  Band A might be tuned to a 70 cm repeater, and Band B might be tuned to a 2 meter repeater.  You will hear both repeaters through the speaker, and will transmit to whichever band you are currently set to (A or B).

Unlike Icom, which also has this dual monitor function, Kenwood does not support the ability to have Band A set to a DSTAR repeater and Band B set to a different DSTAR repeater.  It can only handle one DV connection.  that’s what that fine print note meant.  You can set Band A to DV or Band B to DV, but BOTH A and B can’t be set to DV.

Well it’s easy to understand the limitation (maybe the Icom rigs have two CODEC chips installed), but to understand the implication of what that means to a user is a difficult thing.  In Kenwood TH-D74A world, that means that if Band B is set to DV, and you select Band A as the active one, then the MODE button can’t select DV, and the selector knob on top of the radio can’t select a DSTAR channel.  As a comic once said, “that’s BDONG (Bad/wrong)”.  The user is clearly trying to activate Band A, so why does a setting in Band B continue to take precedence — shut down Band B for heaven’s sake or do something else clever, but don’t be stupid and lock out DV from Band A).

Unfortunately Kenwood support folks don’t understand that, so when my friend called them and said, “HELP, my Kenwood TH-D74A won’t go into DV mode” the support folks were unable to help him — they just insisted that the Mode and Channel selector SHOULD work.  That lead to two very frustrated hams (my friend and myself) being left to figure out how the radio actually worked.

I will give Kenwood props up for a pretty good speech synthesizer — my friend is blind and it’s important for the radio to speak to help him walk through menus.  But even that is only partially implemented in the TH-D74A.  We discovered the synthesizer stops speaking and doesn’t guide the user through anything to do with microSD card.

Posted in TH-D74A | 10 Comments

Fixing the “Solar_Terrestrial Data” Widget

Posted on February 1, 2017 by robert

Paul Herrman, N0NBH, has been providing Solar-Terrestrial Data banners for many years to hams for use on their websites.  One of them is a Widget used by many on WordPress sites, originally authored by Tom, NS6T.  That’s the widget I’ve been using.  However, its behavior with Chrome browsers has been problematic as Chrome seems far more likely to use a cached image than some other browsers.  So when I checked my website today, I saw the following from Jan 13, as opposed to the current Feb 1 info:

Tom’s widget works by going to a specific link on Paul’s website which contains an image that he updates daily.  But that image always has the same name, and that is what confuses the browser into using a cached version of the image. (The link for the image above would be:  http://www.hamqsl.com/solarvhf.php).

I decided to stop using Tom’s widget (not entirely fair, since the problem is with the browser, not the widget itself).  So I changed over to a “Text” widget with the following text:

The key difference is adding the “?<?=rand(1,32000)?” into the img src line.  That information is cached along with the image, and each time that part of the screen is refreshed, the information will be different, causing the image to be reloaded fresh.

So how to do that in WordPress?  Go to Appearance/Widgets:

Either remove the old Solar Terrestrial Data widget, or add a new one using a Text Widget box.  Don’t forget to “Save” when you are finished.

Now I get recent data on my WordPress site.

 

Posted in From the OM | 5 Comments

Winter Field Day — Satellite Success

Posted on January 29, 2017 by robert

I joined Newport County Radio Club, W1SYE, for their Winter Field Day again this year. The weather for New England was fantastic — in the low 40s dropping down to the upper 20s at night.  The only downside was a pretty stiff breeze.  But there was no snow on the ground!

Our WFD had two stations; one on phone for the entire 24 hours, and the other on CW or Digital modes.  Antennas were simple ladder-line fed non-resonant dipoles tuned with venerable Johnson Matchbox balanced tuners.  Power came from a generator, or LiFePO4 battery in my case.

My task was to make a single satellite contact.  I had been planning and practicing the week before, having identified three optimal passes each for  Saturday afternoon and Sunday morning.  As is usual for me, I avoided the FM birds because they tend to be insanely busy.

I had things set up about an hour before the contest began at 1900Z yesterday, and figured I might as well try a SO-50 pass that would be at mid-pass at 1905Z, just a few minutes after the start of the contest.  I spoke with the CW tent and asked them to go off the air between 19:03 and 19:08 UTC, and preset my antenna for the mid-pass Az/El values, planning to have the satellite find me.

Just as expected, at about 19:04 S9 signals came out of the noise, a cacophony of call signs and grid squares.  I put out my info once (W1SYE, FN41, Winter Field Day), WB9YIG immediately returned from EM68 (Indiana) and we are all done at 19:05:25 UTC.

Satellite Station setup in my truck – Icom IC-9100, Toughbook running SATPC32.

Arrow 2m/70cm crossed-beam mounted on tripod. Ax and El were set for mid pass

Posted in Contests, Satellite, SO-50, WFD | Leave a comment

W1YRC Maximum Society Member

Posted on January 26, 2017 by robert

I’m always “selling” the benefits of Amateur Radio to my friends, and one of the things I mention is you get to meet some wonderful people.  I consider myself very lucky to know Bob Beaudet, W1YRC, RI’s Section Manager and avid DXer (on top of many other things).

Bob’s been a strong advocate for the ARRL for many years, and puts his money where his mouth is.  He recently received a batch of QSL cards from the ARRL honoring the fact that he is a member of the Maximum Society.  The Maximum Society is a group of  individuals whose extraordinary generosity continues to support the ARRL, having contributed a minimum of $10,000.  I received one of his card in the mail the other day.

While I belong to the Diamond Club, it will take me many more years to reach Bob’s level of giving.

Nice job, Bob, and thanks for all you do day in and day out to make Amateur Radio fun for all Rhode Island hams!

Posted in ARRL | Leave a comment

Getting Ready for Winter Field Day – Satellite

Posted on January 25, 2017 by robert

Well it’s that time of year again, I’m dusting off the portable satellite gear and making sure it’s working.  I had just updated the clock, and TLEs, when I noticed that UKube was above the horizon.  I quickly turned on the Dashboard and immediately started decoding data packets.

Since it is in daylight, the transponder is off, but it was fun to pick up 46 packets.  This is one of the satellites that will be possible to use on WFD.

At this point I know the control between my PC and IC9100 is working as well as the soundcard interface.  Now to wait for some transponder passes for FO-29, AO-7, SO-50, AO-73, etc.

QSOs were made with the following:

  • On XW-2A, N4IQV, Uplink Calibration was spot on
  • On AO-73, KD2BVM and N4IQV, Uplink Calibration was KHz high, but drifting about 1 KHz lower per minute.  VERY hard tuning a CW station
  • On AO-85, N1AIA & KF4FC — VERY hard to key transponder
  • On FO-29, nary a soul was heard, on either CW or SSB although my downlink was fine.  The pass was mid-Atlantic, so favoring Europe & Africa
  • The later pass around 0325 UTC on FO-29 was more fruitful.  Worked K8YSE, N8RO, HI8KW, and W4CVV.
  • On BY70-1, A new FM satellite for me.  I heard myself quite well in the downlink, better that SO-50 or AO-85, but nobody answered despite 5 minutes of calling CQ.  The delay on the downlink does catch your attention (maybe 100ms).
  • The later pass around 03:45 UTC of BY70-1 was more successful.  Worked N8HM and AA5PK.

Posted in AO-73, AO-85, BY70-1, FO-29, IC-9100, Satellite, UKUBE-1, XW-2A | Leave a comment

VNC Viewer for RPi

Posted on January 5, 2017 by robert

I had no idea that Raspberrian supported VNC connections to the RPi.  I was astounded to find out that a small VNC Viewer Application would remotely connect me to the desktop!

  1. Download “TightVNCViewerPortable” here:  http://portableapps.com/node/32118
  2. Run the installation package.
    (Running it from your desktop will created a folder on the desktop called “TightVNCViewerPortable”
  3. Run the Executable “TightVNCViewerPortable.exe”
  4. Select your RPi IP address and press “Connect” (use the same password as you would use for a SSH session)

5. Enjoy your VNC!

 

Posted in Raspberry Pi | Leave a comment