Category Archives: Accessories

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!

GODAR antennas

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Many thanks to SWLing Post contributor, Mario Filippi (N2HUN), who writes:

[Check out] this site I came by accidentally, small company, USA made antennas, most are OTA TV but he has a few shortwave antennas, quite reasonable. […] Also has old vintage pics. A little of this and that on the website, quite interesting company. He sells on Ebay too.

GODAR USA

Thanks for the tip, Mario. I love supporting mom-and-pop manufacturers like Godar. It appears–based on his eBay rating–that Michael Godar has very satisfied customers and produces quality antennas.

Thanks for the tip!

Let’s talk Raspberry Pi 3 radio projects…

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I just received the recently released Raspberry Pi 3 that I ordered from MCM a couple weeks ago.

Now I’m plotting a few potential radio projects!

Recommendations anyone?

I’d love some input from SWLing Post readers as I’d like to feature a few Raspberry Pi projects here (and I’d certainly welcome your guest posts!).

I’d love to run my RTL-SDR or (better yet) SDRplay RSP with the Pi 3, but I’m sure there are a number of other projects I’ve never considered. I also have the original Raspberry Pi, but what I love about the Pi 3 is built-in wireless connectivity–of course, it’s faster than the original Pi, so I’m sure that’ll help with many radio applications.

Please comment with your suggestions and Raspberry Pi experience! I’m all ears!

Ordering the CountyComm GP5/SSB from outside the US

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SWLing Post readers who are located in countries other than the United States, may have found it difficult (and pricey) to order the CountyComm GP5/SSB portable radio.

I’ve just learned about an eBay seller that ships internationally and works directly with CountyComm. The seller, Randy, is a ham radio operator (KB3GGC) and has a 100% satisfaction rating on eBay, so you can purchase with confidence. His price ($79.95) is also fair and shipping quite reasonable–certainly much better than many of the Tecsun PL-365 listings on eBay.

Click here to view his CountyComm GP5/SSB listing on eBay.

Randy also sells spare antennas and an adaptor that allows to connect external antennas to the GP5 series receiver.

James adds an LM386 amplifier kit to his Heathkit GR-150

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Many thanks to SWLing Post contributor, James Surprenant (AB1DQ), who shares this update to his review of the Heathkit Explorer Jr. TRF AM radio receiver kit:

With regard to the Heathkit TRF AM receiver kit, I did indeed build my LM386 amplifier.

I was planning on home-brewing it from scratch as the chip is pretty much all you need and there are various proven schematics for the circuit, but in the end I went with a small kit from Nightfire Electronics for $10 plus $5 shipping that I found on Amazon.com.

It was a bit cheaper to buy it in kit form, of course, and then there was the convenience of having all the parts in one place.

Here is a photo of the kit as advertised on Amazon…

And here is my build with the Heathkit…

I modified the kit to add a 3.5mm input jack, replacing the RCA jack that came with the kit, to make it easier to plug into the Heathkit radio.

I deliberated whether to install the audio amp into the Heathkit cabinet drilling out a couple of holes for the pot shafts. It all would have fit and I could have easily mounted the 3″ 8 ohm speaker to the back panel of the Heathkit radio. In the end, I decided to keep the radio original and mounted the amplifier board on a small piece of wood I found at a hobby store and decided to leave it all exposed. It works well, all things considered.

(Click here to view video on Facebook.)

It worked well and per my original review on SWLing Post, I feel Heathkit should have included such a little amp in the kit – it makes a big difference.

Many thanks for the update, James! That little LM386 amp kit seems like an affordable addition for any receiver lacking an amplifier or adequate audio amplification.

Mike’s Virtual Audio Cable (VAC) promotion

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SWLing Post contributor, Mike Ladd, has been working with vendors to lock in promotional pricing on products and accessories commonly used by SDR enthusiasts. Last week, for example, he shared an excellent promotion for high/low pass filters.

This time, Mike has reached out to the author of Virtual Audio Cable (VAC) who has also kindly offered a discount.

VAC is a fantastic piece of software that allows you to port audio from one application to another on your PC without loss of audio quality. For example, if you’re running an SDR and you want to port its audio to FLDigi (to decode SSTV, RTTY, PSK31, or another digital mode) VAC does this for you.

Mike’s discount allows you to purchase a self-support copy of VAC for $21.42 US (a $3.78 discount).

To get the promo price, you’ll need to use this link which has the embedded coupon code, then simply make the selections as shown below:

Click here to purchase VAC with promotional pricing.

Thanks again, Mike, for sharing discounts with the SWLing and ham radio communities!

Portable power for active antennas

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CPI1000 mit Powerbank

Many thanks to Dennis at Bonito for sharing a link to an article he recently published on the Bonito blog:

Autonomous power supply of our active antennas via USB and power bank

It is getting to be more and more difficult to procure reasonably priced analogue external plug-in power supplies because just like old light bulbs they are no longer allowed to be produced due to power consumption restrictions. We are spending a lot of time to find and buy remaining stock so that we can offer our customers noise-free external power supplies. But for years, there has been an alternative.

Our MegaLoop ML200, ML052, the MegActiv MA305 as well as the GigActiv GA3005 can be operated internally with as little as 5V and so can be powered by the supplied CPI1000DP / CPI3000DP bias tee via a USB cable. In light of the annoying switching power supplies, PowerLAN and heightened mobility of listeners, this is a very practical alternative and offers much more flexibility for the customer. Unfortunately, this fact is not well known and that is why I would like to shed some light on this subject.[…]

Continue reading at the Bonito website.

Thanks, Dennis!

I should note that there are a multitude of 5 VDC powerblocks on the market. I have two made by Eton Corp (see above) that even have hand-crank power generation. I recently used one to power my Raspberry Pi (Raspberry Pirate!) for several hours.