First Radials on the Ground for Inverted L

Posted on June 3, 2017 by robert

I’ve been using a low loop, about 450 feet of wire, around 20 to 30 feet off the ground for years.  It worked well for me, enabling me to get 9-band DXCC and 8-band WAS.  But the sunspots have diminished, and longer wavelength bands are coming into their prime.  I’d really like to get DXCC & WAS on 160 meters.  A low loop is a cloud warmer at that frequency.

The new plan is to install an inverted-L antenna.  It will have a 55 foot vertical element, then run horizontal to the ground for another 90 feet +/-.  That wire will be attached to a remotely tuned L-Network which is coax fed.  Since the tuner will present a 50 ohm load on the coax side, the feedline loss will be minimal.

A decent radial system will be required for the Inverted-L to work effectively.  So far only 5 radials are on the ground (each 123 feet long), and more will be installed before the first snows this winter.  I’m hoping that this start will be enough to give things a try on 160 and 80 meters.

 

Posted in Antennas, DX, Propagation, Testing | 1 Comment

Amazing LOTW Participation in NEQP

Posted on May 9, 2017 by robert

I just uploaded my New England QSO Party log to LowT and was expecting a few confirmations.  I was stunned when I saw that 60% of the 163 QSOs I uploaded were already confirmed not even 48 hours after the contest conclusion.

As an interesting tidbit, eQSL only had 14% confirmations despite the fact that many log programs automatically update eQSL.  Just shows how it is slowly dying off.

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New England QSO Party Fun

Posted on May 7, 2017 by robert

I don’t recall ever operating in the New England QSO Party before, but several emails were circulating encouraging activity, so I thought I’d give it a go.  Conditions were OK on the lower frequency bands — not a lot of noise.  15-meters even opened up for a brief time Sunday afternoon on a North/South path.

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Replaced my Mobile Mount Today

Posted on April 14, 2017 by robert

Back in March of 2013, I installed a Diamond K9000 Motorized Antenna Mount. Unfortunately it started acting up about five months ago after about 3.5 years of service mounted on a truck that leaves its garage about twice a week, and an antenna that has been raised/lowered less than 100 times.  Needless to say I wasn’t happy.

I was even less happy when I opened the failed unit up and found that it obviously been filled with water at one point as many parts were heavily rusted, despite weep-holes intended to allow the water to drain.  Another issue was discovering a cheaply made limit switch that turns the motor off when in the stowed position.  This was very odd considering that a real snap switch was used for the other limit switch (a SPDT used in the raised position).

The unit was purchased new in early 2013.  The final surprise was discovering that it had been fabricated in 2008 — meaning it had hung around in inventory for 5 years!  Given the lack of quality of the broken limit switch, even having it sit around probably caused the contact to oxidize.

Given the cold weather I waited until spring to swap it out with a new one.  This one appears to be new 2016 inventory.  Hopefully it will last longer than the first one.

Poorly fabricated Limit Switch (Lowered Limit)

Visible Rust in shell (where bottom of motor frame is attached)

Metal Frame of Motor Bracket rusted (likely that water was in raised limit switch too)

 

 

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How Well Does the Pixie Receiver Work?

Posted on April 11, 2017 by robert

My club, Newport County Radio Club, just completed our third and final meeting on the 40-meter QRP Pixie kit.  We packaged the inexpensive Chinese QRP kit with sockets for the crystal and final transistor, two additional crystals (7.030 and 7.040) to go along with the stock Extra Class-only 7.023, and a 2N2222 to be used in place of the stock final.

We did this as a club build project, setting up multiple assembly and test/rework stations. In the end, about two dozen Pixies were built.  All but four of them worked right out of the box.  Two had cold solder joints.  One had a solder bridge.  The only “mystery” turned out to be a LM386 that was on the high-side of its maximum current spec, which caused its power source to collapse.  Everyone managed to get the right components into the right locations and there were no missing parts.  All of the kits produced from 300 to 500 milliwatts output power.

Another question was how well did the receiver perform.  My expectations were quite low as the entire receiver circuit consists of a fairly inadequate LPF (see multiple posts about a Pixie LPF that actually meets FCC requirements), followed by a gimmick mixer (the final transistor), and a LM386 audio amplifier run wide-open gain.  After testing a bunch of Pixies, a pretty reasonable performance specification would be:

  • RX MDS -76 dBm (25 microvolts)
  • -73 dBm is full copy but weak (this is S9)
  • -33 dBm is ear splitting (S9 + 40 dBm)
  • Selectivity is in excess of 10 KHz

Those are pretty bad specs, but what would one expect for a few dollars?  The RX does work and many of our kit builders have used their radios on-air with great success.

Posted in Pixie, QRP | 1 Comment

First Quarter 2017 DX Results

Posted on April 1, 2017 by robert

February and March were pretty good for me at my current snail’s pace, adding three new countries for a total of 261, and bumping the band-point count up to 1,237.

So even near the bottom on Cycle 24, there’s still DX to be had, but 40 meters is now yielding better results, and there is very slim pickings on 10/12/15 anymore. So now I have to be content with working a station on one or two bands rather than six or eight.

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Using a Diplexer (Duplexer) as a 2-meter LPF

Posted on March 28, 2017 by robert

First off, to be clear, I’m talking about a Diplexer, the small device that will fit in your pocket and costs < $60, that is used to combine 2-meter and 70-cm rigs to use a single antenna feed-line. However both Comet and Diamond call these things Duplexers which are usually large multi-cavity devices that cost > $1000 that certainly won’t fit in your pocket.

Some discussion on the AMSAT forum recently has centered around eliminating those pesky 3rd harmonics from inexpensive HTs that don’t meet FCC specs.  Folks were complaining of having 70-cm receive desense when transmitting on 2-meters.

A suggestion was made to use a Diplexer, since it is not much more than a LPF on the low-frequency port and a HPF on the high-frequency port.  I was curious if they met their performance specs and if it made a difference if the unused port was terminated or not.  The executive summary is Yes, and Yes (although termination isn’t a huge deal).

I used my recently calibrated Siglent SSA3021X to test a Comet CF-4160J “Duplexer”.  I normalized my SA and the interconnection cables I would be using, then hooked a Comet DF-4160 “Duplexer” into the path with the High Frequency Port terminated as seen in the photo below.

When I swept the Low Frequency Port side, the response was pretty much as expected from Comet’s specifications.  There was about 0.12 dB of insertion loss and the 70-cm response was down -55 dB.

I disconnected the 50 Ohm termination and observed a rather dramatic change in the response as seen below.  Note the rather pronounced dip around 300 MHz.  The loss increased slightly to -0.13 dB, and the rejection was reduced by 3 dB to -52.  So the advice would be to terminate the High Frequency Port.

Just for grins I swapped the Common Port and Low Frequency Port and found the results to be essentially identical to my first test, so which way you hook it up doesn’t matter, as you might expect.

Posted in Projects | 1 Comment

KA1QYP Half Pint QRP Transceiver Passes FCC

Posted on March 24, 2017 by robert

In our continuing quest to evaluate the output purity of various QRP kits, Willy W1LY constructed a Bill KA1QYP Half Pint Kit.

The assembled kit produced a solid 600 mW output and was one of the cleanest radios we’ve seen.  The worst case was the 3rd harmonic which was -59 dBc.

The Half Pint uses a Cauer Filter, similar to a 5-pole LPF but two of the sections are tuned to suppress the 2nd and 3rd harmonic frequencies.

The Elsie Predicted response is shown below.  Note the pronounced dips at the harmonic frequencies.  Loss at 7.040 MHz is about 0.9 dB, and the 3 dB knee is about 8.1 MHz:

The measured performance is shown below.  The 2nd harmonic is down about 63 dBc, and the 3rd harmonic is down about 59 dBc.

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Pixie with 5-pole Axial Filter Passes

Posted on March 14, 2017 by robert

Willy, W1LY, decided to try using the standard unshielded 1 uH axial inductor that the Pixie uses for it’s current 3-pole filter (C5=47o pf, L2=1 uH, C6=470 pF) as the starting point for a 5-pole filter that could easily fit on the existing board.  Two inductors are soldered in place of L2, standing up vertically and soldered together at the top.  A cap is then soldered from that bridge down to the grounded side of C6 (Willy paralleled two caps to get the required value).  See the area indicated below.

 

Component values are:

  • C5 changed to 820 pF
  • C6 changed to 820 pF
  • New Cap (bridge of L2A/L2B to ground at left side of C6) 1150 pF (680+470)
  • L2A (1 uH)
  • L2B (1 uH)

Measuring the output of the modified Pixie indicates a passing value!  The 2nd harmonic, worst of the lot, was -43 dBc.  Power output was 0.3 watts using a P2n2222 for Q2.

We suspect that original 5-pole Elsie values of 1.2/1.2 uH and 910/1300/910 pF would produce even better 2nd harmonic suppression and work just fine at the lower end of 40 meters.

Posted in Pixie, Projects, QRP | 1 Comment

Elsie Plot of QRP-Labs 7-pole 40-m LPF

Posted on March 5, 2017 by robert

This is the schematic of the 7-pole LPF used in the QRP Labs 40-meter LPF:

The plot from Elsie 2.77 for the above filter looks like this:

The actual SA response curve looks like this:

The curves are remarkably similar.  Knee around 8.8 MHz, about 36 dB down at 14.08 MHz.  Loss at 7.04 MHz is a bit worse on Elsie, but that is based on Q values of 40 for the coils and 200 for the caps — both are probably a bit better.

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