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QSL: Buro or Direct (See Bio)

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Ham Member Lookups: 1924

 

1/4 WATT QRPp DX...  WITH SOFTROCK SDR

I started writing this page to show an example of what can be done at QRPp power levels; then it continued to expand...  :-)   After retiring in 2013 I discovered SoftRock SDR and in an 18 month period, from June 2014 through Nov 2015, I worked 100 DXCC prefixes including all continents with a 1/4 watt SoftRock and "Rocky" software. The most recent prefix is YO9, bringing the total to 116.

SoftRock RF output is partly controlled by computer sound card line out voltage and output from my "on board" Realtek card is low. It drives the SoftRock to about 260 milliwatts on 20 meters with a very conservative 12.0 volt regulated power supply (7812, a diode and a few caps); RF output on other bands varies by a few milliwatts. A better card would drive the rig safely to about 1 watt.

Rocky freeware software written by Alex VE3NEA for the SoftRock is perfect. It has a simple interface, does everything that needs to be done and its horizontal full screen waterfall mode is exceptional; I never leave that screen.

Contest DX:  CQ WW Contest 2014 is shown in "Rocky" in the photo below, with 14.000 MHz at the bottom and 14.060 at the top. This was a good weekend with 15 new prefixes including Morocco, Kuwait and Cyprus. CQ WW in 2015 did not produce much new.

  

CQ WW in 2016 had a few moderate openings on 20m and 15m. I wasn't able to work any new prefixes but on Sunday Pacific Time I did work NA, SA, EU, Asia and Australia at 1/4 watt plus Africa at 5 watts (CN2 Morocco with the FT817ND) to make a total of 5 continental regions QRPp and 1 QRP. Unfortunately I couldn't find an operator in Antarctica to WAC in a single day.  :-)

Expeditions:  Pile ups look hopeless at very low power but sometimes you get lucky, K1N Navassa and 9Q0 Democratic Republic of the Congo were good ones. VP8SGI South Georgia Island took several days; expeditions are usually easier in their final week. There were many others.

A 1/4 watt seven band sweep of TX7EU Marquesas Island on 40 30 20 17 15 12 and 10 meters took about a week with moderate openings on at least one band most days. The very short morning greyline pileup on 40 was from EU over the pole; the OP worked a Russian call a few seconds after working me. His path was almost directly overhead in the twilight. The expedition used horlzontal dipoles on a bluff over the beach looking toward NA, ideal for VE7. 

RI1ANZ at the "Russian Progress Station" in Antarctica is my longest distance; Nikolai was running a steady string on his call frequency, not piled up and a relatively easy contact in the clear. Antarctica is not a difficult path from VE7, but active stations are hard to find.

Routes:  Paths from VE7 into the Pacific and Oceania are easy but working with 1/4 watt over the pole across EU into Central Africa, Southern Africa and the Southern Ocean is very difficult; it's no surprise that paths over salt water are easier than those over land.

Video:  I got lucky when Sam FK8DD/M posted a video of our QSO, we don't often hear our stations on the air.  https://www.facebook.com/sam.torope/videos/10204674108201336/  Sam was working mobile with a multi-band vertical on the roof of his van.

 

Beam on 20 15 12 10 Meters:  Most of the QRPp DX was completed on an old XP-505 beam up 13 meters. This beam was designed by DJ2UT (now SK) in Germany and sold in the 1980's; the XP-505 without any extra kits is designed for 20, 15 and 10 although the longest element (39 feet)  loads as a shortened dipole on 30 and 40.

Five of the six elements are live with a phased log cell type feed; there is no conventional driven, reflector or director element, nor are there any traps or loading on 20, 15 or 10.

On 20 meters, gain is approximately 7 dBd (over a dipole at the same height and position), 15 and 10 are similar; proof of performance is one hundred prefixes in 18 months QRPp.

 

40 Meters:  This dipole is broadside to the SE and overlooks a 100 foot bank. It gets out much better than it receives and works reasonably well into southern VE7 and the US but not so well any where else. It isn't a DX antenna, although a few 1/4 watt ATNO's were possible into SA, Oceania and Asia.

The enclosure at the feed point is a simple LC impedance matching circuit; 80 ohms down to 50 ohms for the RG-213.

 

80 Meter End Fed Half Wave Wire (EFHW)... Sloper to the SE:  Feed point impedance on an end fed half wave will be several thousand ohms and in this photo you can see the feed at about 32 feet with the 125.5 foot wire sloping down to the right and the "counter poise" to the left. The coil below the match enclosure is a "common mode choke" with 8 turns of RG58 through 3 RFI split cores for about 10000 ohms on the braid.

 

I'm using Yate's link coupled tuned circuit described in his long paper http://www.aa5tb.com/efha.html and his one page summary at http://www.aa5tb.com/efha_wrk.html , both present possible link ratios but these are all guesses. There is no easy way to know wire end point impedance |Z| or the R component of |Z| with any accuracy unless you can get an analyzer in the air to make some measurments; values will be in the 2000 to 4500 ohm range.

After some trial and error I ended up with a 28:3 ratio on a T200A-2 core with an air variable cap. The match isn't perfect, but it is close enough to 50 ohms to work well .

 

80 Meter Horizontal Half Wave Wire (Off End Fed)... Broadside to the SE and NW:  This wire is a work in progress, an experiment with an average height of about 28 feet and at right angles to the sloper described above. You could think of it as a 125.5 foot resonant Half Wave that is fed 6.5 feet from one end or as a 119 foot End Fed Wire with a 6.5 foot counterpoise. Electrically, there isn't much difference other than the name. The feed point is near the tower end, up about 30 feet, using a simple LC circuit.

Initial testing shows signals down about 1 S unit to the SE compared the sloper; this result is predicted in an EZNEC model, so no surprise there. My real goal is to improve signals to VY1 to the NW where the EZNEC prediction is to be up at least 1 S unit over the sloper; I am hoping for 2. If I don't get at least 1 unit I won't bother keeping it over winter, the installation is marginal.

The LC impedance match from the 2000 ohm feed point is close to 50 ohms and bandwidth is broader than with a Yates link couple (for what that's worth).

 

PORTABLE ANTENNAS:

A Portable Multi Band Wire Strategy:  One approach is to use non resonant, tuner friendly wires to avoid high impedance high voltage end feed values (4000 ohms would be high, 2000 ohms not so bad); lengths suggested in literature are 29, 35.5, 41, 58, 71, 84, 107, or 119 feet. To avoid RF on your rig, use a counterpoise.

Choose a "non resonant" wire length more than 1/4 wavelength on your lowest band. If you want to work 40, 20 and 15 from a small campsite, 41 ft would work. Cut a counterpoise (rarely a 1/4 wave).to make the combined wire lengths add to a half wave on the lowest band; 25 feet would work with 41 in the air.  The 66 foot total is approximately a half wave on 40, a full wave on 20 and 1.5 wavelengths on 15; this 41/25 combination works well on all three bands.

You might get by with a single counterpoise but sometimes you need a second or even a third for multibanding. On higher bands, think about the number of half waves on the combined wires when you calculate and cut a second counterpoise.

For 17 meters you could use 41 feet in the air with a 10 foot counterpoise for 51 feet total, approximately 2 half waves at 18.1 mHz.

For 80 meters you could use 71/54, 84/41, 107/18 or 119/6, its your choice depending on the site, but usually the more wire in the air the better (each of these adds to approximately 1/2 wave on 80). Tweak the counterpoise not the wire for the portion of the band you need. Use a simple LC circuit or an auto tuner to match the feed point to the rig but keep in mind that the shorter the counterpoise, the higher the impedance; a 119/6 feed will be more than 2000 ohms. 

 

Short Wire Multiband Results:  In a summer 2017 camp, I started with the 41/25 combination for 40m, 20m and 15m. However, with the support cord over a 60 foot birch (sling shot, weight, mono fil fishing line to get started) I decided to change the 41/25 ratio to 56/10 to get more wire in the air and less along the ground (56 feet isn't in the list but it's close enough). Overall length was still 66 feet, although feed point impedance on 40m increased from the 75-150 ohm range up to about 800 ohms.

On July 8, 2017 with the 56 foot segment sloping up at about 60 degrees above horizontal and the 10 foot counterpoise stretched away from it about 2 feet above ground to the SE (let it radiate), this "56/10" worked a dozen contacts on 40m and 20m in the US.

On the same afternoon on 20m and 15m, it heard 10 countries including New Zealand and Belgium and worked 5 countries including Hawaii, Japan and France. I also used it daily for net checks on 40 and 80 in VE7/VE6. All contacts were at 5 watts with the FT-817ND; DX was on CW, some of the net checks were on LSB.

 

Longer Multiband Wire Results:  At a summer lake cabin location I use a semi permanent 119 foot "Inverted L" with a 12 foot counterpoise and the little MFJ LC tuner for 80, 40 and 20. From the feed point, the #14 stranded insulated wire slopes up at 60 degrees and over the crowns of a small group of cedars and birch at about 55 feet; the far end of the wire slopes down to about 50 feet.

Feed point impedance on 80 is approximately 2000 ohms and the matches at the tuner on the three bands are 1.1 to 1 on 80m (photo below), 1.3 to 1 on 40m and better than 1.1 to 1 on 20m.

This wire hears much better on 40 meters than my dipole in town.

 

Portable Wire Comments:  All wires plug straight into the tuner, usually on a table beside the rig under the tent fly. The counterpoise ( from the tuner case/ground) usually stretched away, elevated about 2 feet; let it radiate. With this configuration its sometimes worth thinking about the system on the lowest band as an off center fed low bent dipole, rather than an end fed wire with counterpoise.

RG58 from the external tuner is about 3 meters long, 2 meters of which is used for the common mode choke between the tuner and the rig. Matching is always stable and stray RF on the rig has never been an issue.

"Antenna tuner" is a misnomer; we usually bring a system to resonance by tweaking wire length (counterpoise here). Impedance matching at the feed point or at the rig is a separate issue. Resonance and impedance are relatively independent.

With the non resonant antenna wire sloping up to a tree branch and the counterpoise stretched away from it and elevated, the antenna will favor the counterpoise direction.

All of these simple portable antennas are simple classic designs, the only difference is counterpoise strategy. There was no need for it to be a 1/4 wave on any band on any wire. The only combination that might require a 1/4 wave counterpoise would be a 1/4 wavelength (or odd multiple) in the air.

All wire antennas are works in progress, there is always room for improvement.  :-)

 

QRN, RFI and Common Mode RF Chokes (for EFHW and Other Wires):  RF chokes on the braid at the feed point are effective in attenuating RF common mode currents. Mine partially solved a touch lamp "triggering" problem in the house.

An unexpected bonus is that these chokes can also be effective in reducing QRN. Local city noise picked up on the outside of the braid flows up to the feed point and then down the line to the rig (I think). Most of this braid pick up can be choked off at the feed point (and at the shack). On my 80 meter EFHW, a three core choke at the feed point combined with a 2 core choke under the soffit has reduced local noise sources by 3 to 5 S units on my IC735.

A choke with 8 turns of RG58 through 3 RFI split cores can produce more than 500 uH. Assuming that I have the formula right;  Impedance = 2 * Pi * (Inductance in mH) * (Frequency in kHz)  500 uH would calculate out to about 10000 ohms on 80 meters and 20000 ohms on 40 meters.

Sometimes local QRN can be reduced with physical separation, moving the antenna further away from electrical wiring. To avoid close coupling, don't run an antenna leg over your roof; end feeding can help here.

Zip ties squeeze the gap and increase impedance by up to 50%

 

Personal:

My first interest with radio was in the 1960's with crystal sets and with short wave listening on old tube table radios; most had short wave bands. In the 1980's I finally got my ham license and was very active for about 10 years, with construction projects, towers, beams, repeaters, packet radio, field days, club activity etc. etc..

I was relatively inactive through the 90's and until retirement from work in 2013. Since the 1960's I have had careers in geological engineering, fixed wing bush flying, helicopter flying and finally education. Now I am back into ham radio with SDR and other new interests.

I don't chase paper awards, however I would be pleased to receive QSLs for CW QRPp contacts and will do my best to return the favor, your choice, BURO or DIRECT.

73 Bruce 

8351230 Last modified: 2017-09-25 22:23:13, 32391 bytes

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