Category Archives: Ham Radio

Guest Post: Building a magnetic loop antenna & broadband amplifier for your SDR

Many thanks to SWLing Post contributor, Dave Gahimer (K9ZCE) for the following guest post:

Small Magnetic Loop Antenna with Broadband Amplifier for SDR Reception

by Dave Gahimer (K9ZCE)

Those with limited space, or antenna restrictions, might find a small 1 meter loop antenna a solution.

My son lives in an apartment. One Loop leaning against a wall gives him acceptable reception with the SDRPlay RSP on the ground floor–2nd or 3rd level flats should have very good reception.

Ten meters off the ground outside should give reception equal to any SWL antenna. We all with SDRs fight the image problem. Normal resonate ham band antennas show too strong reception of unwanted bands/stations. Did I mention noise? Loops are well known for –6 db noise reduction.

Then there is the possibility of SDR chip damage from your 1.5 KW station! In researching Loops we came across LZ1AQ. A Brilliant design /engineer (http://www.lz1aq.signacor.com/). Deep reading sometimes, but a great understanding of what makes a good receiving loop antenna.

Those who chase DX know that sometimes fading is caused by the signals’ polarization changing in the Ionosphere. Having both vertical and horizontal loops, and the ability to combine both signals diminishes this fading problem. Being able to filter the powerful, commercial FM transmitters diminishes image problems. Clipping strong signals at the antenna from very near powerful antennas/transmitters could save the SDR receiver from damage.

The LZ1AQ broad band Amp solves all these problems. http://active-antenna.eu/amplifier-kit/.

My son Ted and I built three, one meter loops from soft ½ inch copper plumbing tubing. One for his apartment, two for my crossed loops antenna. We weather proofed the Copper from corrosion by coating with outdoor clear spar varnish. We shaped the circle by drawing the tubing around a round glass top patio table.

The soft copper loop in held by white PCV plastic plumbing pipe. 1” or 1.25 inch schedule 40. Be careful to check that the PVC is schedule 40, thick wall. The thin wall pipe is not strong in the wind and will crack when you try to drill it.

Drill up to a 3/8 hole for the ½” copper tube to go through, then file out to fit. Here are some photos (click to enlarge):

Check out these links (all courtesy of LZ1AQ) to acquaint yourself with the loop construction and amplifier installation:

http://active-antenna.eu/tech-docs/2_ActiveAA_Mount_20.pdf

http://active-antenna.eu/tech-docs/1_ActiveAA_DandS_20.pdf

http://active-antenna.eu/tech-docs/3_ActiveAA_Antena_11.pdf

Many SDR receiver owners have seen improved noise and Image reduction by placing the plastic cased SDR unit on a small shielded/ grounded case.

The Amp needs 12VDC from in the shack. The Amp has two relays that you can switch, from in the shack, to select Vertical or Horizontal loops, or a dipole. The loop amp connects back to the shack via a shielded Cat 5 cable, Make sure you get shielded CAT 5 to reduce noise pickup. Make sure you provide an adequate good Ground below the antenna, less noise pickup and lightening protection.

Have fun!
Dave, K9ZCE
Retired from EE Dept @ Rose-Hulman Institute of Technology
Terre Haute, Indiana

Thank you so much, Dave!

Readers: yesterday I saw Dave’s loop antenna photos on the SDRplay RSP Facebook page. I was fascinated by his horizontally/vertically oriented loops and asked if he would write up a short guest post. He kindly obliged in a matter of hours!

If you have an antenna project you’d like to share, please contact me. So many SWLs and ham radio operators live in areas with restrictions and pervasive RFI–projects like Dave’s can revive one’s radio life!

Heard Island DXpedition (VK0EK) live via WBCQ tonight

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(Source: ARRL)

[…]At 0000 UTC on March 23 (the evening of Tuesday, March 22, in US time zones), Tom Medlin, W5KUB, host of the weekly “Amateur Radio Roundtable” video webcast and radio program, hopes to make ham radio media history by interviewing the DXpedition team live on his webcast. Audio will be simulcast on international shortwave broadcaster WBCQ on 5130 kHz.

Heard Island is an Australian protectorate, part of a subantarctic island group(Heard Island and McDonald Islands) in the southwest Indian Ocean, some 4000 kilometers (approximately 2480 miles) southwest of Western Australia and 1000 kilometers (approximately 620 miles) north of Antarctica.

I will certainly be listening to WBCQ tonight and, hopefully, recording the show for the SRAA.

For updates about the Heard Island DXpedition, check out their website (and admire Jeff Murray’s excellent official DXpedition artwork while you’re at it!).

Listening to the International Space Station (ARISS) with a Yaesu VX-3

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Yesterday, my buddy Eric (WD8RIF) sent the following message:

“Take your girls outside with an HT and listen to the ARISS pass in just about 10 minutes. The downlink freq is 145.800.”

Though I was in the middle of another project, I took Eric’s advice: I grabbed my Yaesu VX-3, corralled my daughters and ran outside. Eric’s message was already eight minutes old when I read it, so I only had about two minutes to get ready.

My Everyday Carry (EDC) pack, loaded with all of the essentials.

Fortunately, I always have a Yaesu VX-3R loaded with fresh batteries in my EDC pack (above).

Official NASA portrait of British astronaut Timothy Peake. Photo Date: August 28, 2013. Location: Building 8, Room 183 - Photo Studio. Photographer: Robert Markowitz

Official NASA portrait of British astronaut Timothy Peake. Photographer: Robert Markowitz

With the VX-3 tuned to 145.8 MHz, we waited as the ISS made its way above the horizon. The downlink audio of astronaut Tim Peake (KG5BVI) communicating with Walter Jackson Elementary in Decatur, Alabama, started to punch through the static after a minute or two. We listened the entire time we had line-of-sight to the ISS–about five minutes or so. We were pretty deep in a valley at that point, so I’m pleased we were able to catch even that much of a pass.

Of course, we could only hear one side of the conversation: the downlink from the International Space Station.

It was a memorable event for my girls who have seen ISS passes at night, but had never heard live audio from an astronaut before.

Here’s a short video of two of the exchanges we heard:

(Click here to view on YouTube.)

Eric pointed me to the ARISS “Upcoming Contacts” (http://www.ariss.org/upcoming-contacts.html) page where future ARISS QSOs are listed. Evidently, this particular ARISS QSO was the third Eric had monitored in two weeks.

Pretty much any receiver that can tune to 145.80 MHz FM–or a VHF scanner–can hear the ARISS downlink as long as the ISS is passing overhead during the transmission. Of course, if you have a high-gain antenna that can track the ISS as it moves across the sky, you’ll get even better results than I did with my basic rubber duck antenna.

My advice? If you want to impress a child (or your inner child–!) find a little time to listen to a future ARISS QSO!

Indeed, the next step for me is to see if I can propose an ARISS QSO for our school group!

Mark’s Icom IC-7100 go kit

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Click to enlarge

Many thanks to SWLing Post reader, Mark Hirst, who writes:

Thomas,

I have been very impressed by the shacks featured on SWLing !

I don’t really have the room to accommodate such large collections, or to dedicate a special area to just radio.

I tend to perch a radio on a spare surface in the front bedroom, and then cycle through my small collection on a weekly or bi-weekly basis, returning the previous radio to storage to await its turn in a month’s time.

Since newer houses and gardens are typically quite small in the UK, I’ve always been thinking in terms of radio on safari, so with the weather starting to improve, I present to you my ‘shack’ consisting of a recently acquired IC-7100 inside a fortuitously sized toolbox. The radio runs in the bedroom like this too, usually connected to a Wellbrook loop when not transmitting.

The picture [above is of the] head unit in stowed configuration, as the lid of the box doesn’t quite clear the unit when sitting on the base. The space on top of the radio is then filled by the SOTA Beams antenna bag and other sundries. The battery travels separately in the backpack.

My plan was to never have to connect/disconnect the ethernet style cable between the two halves, looks like the plan worked !

You can see it in action here:

This is a brilliant kit, Mark–a great way to escape urban radio interference! The Icom IC-7100 is uniquely qualified for the deep case, too, since the control head can sit on top of the body while in use. The angle of operation is also ideal. Very cool–thanks for sharing!

Stuart Sizer: Heathkit designer, dad, and “bon vivant”

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Two weeks ago, through a radio preservation group, I met the son of Heathkit product designer of the 1950s-70s, Stu Sizer––”stylist, artist, maker of models, bon vivant.” His son described the discovery of a few vintage Heathkit brochures, photos, and illustrations his father kept in his family’s basement shop, many of which had been scanned at some point.

Stu Sizer––”stylist, artist, maker of models, bon vivant”––was tasked with crafting Heathkit’s user-friendly and attractive exterior designs. For many years Sizer was Heathkit’s only product designer, and was therefore often busy. “He was a great dad,” his son told me, “but he spent a lot of time in the basement proof-building kits.” He adds wryly, “Let that be a lesson to the hams of this world.”

Sizer’s son kindly shared with us the following scans and photos of his dad’s work, many of which are original drawings; the series concludes with some clippings featuring Sizer.