Category Archives: Antennas

Radio World: History of Directional AM Broadcast Antennas

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Many thanks to SWLing Post contributor, Marty, who shares the following article by John Schneider in Radio World:

In the early years of AM radio broadcasting, all stations utilized non-directional antennas. Most all of these were wire antennas suspended between towers or buildings. Interference, especially at night, was severe. An interfering signal of 5% or less in signal strength was enough to disrupt reception of the desired station, and if the frequencies of the two stations were slightly separated, there would be a heterodyne beat note. As a result, only a few widely-spaced stations could operate on each of the AM broadcast channels in the entire country at night. This limited the number of stations that could coexist to about 500 nationwide, with many of them sharing time on a single frequency.

As antenna technologies were developed and improved in the early 1930s, a few progressive stations began experimenting with multi-element directional arrays. This approach offered two attractive benefits: 1) It could reduce radiation towards other stations on the same or adjacent frequencies, permitting more stations to share a frequency; and 2) a broadcaster could direct more signal towards the desired coverage area, and away from wasted areas such as open water in the case of coastal stations.

WFLA-WSUN

The first known use of a directional antenna was by a pair of stations in Tampa/St. Petersburg, Fla. In 1927, the Clearwater Chamber of Commerce acquired station WGHB and changed the call sign to WFLA. A companion station, WSUN, was operated by the St. Petersburg Chamber of Commerce. The two stations shared the frequency of 900 kHz, broadcasting on alternate evenings to promote tourism and business opportunities in their respective communities. In reality, they operated with two station licenses, but there was only one transmitter and one antenna.[…]

Click here to to continue reading the full article in Radio World.

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August 2019 Rockwork DXpedition

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Many thanks to SWLing Post contributor, Gary DeBock, who shares the following guest post and update from the August 2019 Rockwork DXpedition:

Gary DeBock DXing with Craig Barnes at the Rockwork 4 ocean cliff near Manzanita, Oregon, USA

Once again the largest FSL antenna collection on the planet made its way across the Columbia River bridge during an overnight trip to NW Oregon, finally being deployed at the original Highway 101 plunging cliff turnoff– Rockwork 4. There has been a drastic decrease in the squatter population, so that Craig Barnes and I were able to easily set up all four PVC bases for all-out DU-DXing at the dream site this morning (see photo). Unfortunately Chris Black came down with a health issue at the last minute, and needed to cancel out.

Craig and I had some excellent signals from the regulars (including 531-More FM, 558-Fiji and 1017-Tonga), although it wasn’t quite a stellar morning for rare DX. We were kind of spoiled last year with 1017-Tonga staying a S9 practically throughout the session, but this morning it was “only” at S9 for a few minutes at a time. This meant that as soon as I notified Craig of 1017’s potent status, the signal tended to nosedive. Maybe the cumulative effects of humidity and salt water exposure are beginning to take their toll on the Tongan big gun? 558-Fiji showed up with decent signals for a couple minutes at a time, which meant that Craig got the short end of the stick after I notified him of the potent signal. 531-More FM hit an awesome S9 peak around 1312 (including the usual split-second female ID), making it once again seem totally bizarre that no trace of the 2 kW modern rock station has ever been received at Grayland for the duration. The Rockwork Cliff is typically focused in like a laser on New Zealand, and this was a typical morning!

531 More FM Alexandra, NZ 2 kW Potent S9 modern rock signal from this Rockwork regular, with female “More FM” ID at 19 seconds:

Click here to download.

558 Radio Fiji One Suva, Fiji 10 kW Island music at temporary potent level at 1257; typically hit the skids after reaching this level:

Click here to download.

1017 A3Z Nuku’alofa, Tonga 20 kW Female Tongan speech at S9+ level at 1317:

Click here to download.

1017 Newstalk ZB Christchurch, NZ 10 kW Presumed the one under A3Z’s meltdown-level signal:

Click here to download.

73 and Good DX,
Gary DeBock (DXing with Craig Barnes at the Rockwork 4 ocean cliff near Manzanita, Oregon, USA)

DXpedition equipment:

7.5″ loopstick CC Skywave SSB and XHDATA D-808 Portables
15″, 15″ and 17″ Airport Unfriendly FSL antennas (see photos above)

Again, thank you so much for sharing your DX, Gary! I’m so amazed by the signals you snag each year with your homebrew loopstick antennas!

To read more of our posts by Gary DeBock, click here.

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LZ1AQ Evaluates Impact of the Height Above the Ground on Mag Loop Performance

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Source: LZ1AQ

Many thanks to SWLing Post contributor, Harald Kuhl (DL1AX), who shares the following article on LZ1AQ’s website:

Published on: 2018/11/20, Rev. 1.0 July 2018, Rev. 1.1 Nov 2018

Author: Chavdar Levkov LZ1AQ

Setup

Two identical small loops were placed one above the other according to Fig.1. One of the loops is very low – almost on the ground. The other one is placed at height which usually is used by the loop users. Two AAA-1C wideband active antenna amplifiers were used. Their gain difference was not more than 0.3 dB. The feeder was FTP cable each 20 m long. No cable baluns were used. The outputs were connected through two way antenna switch to a SD RX (Perseus). I used a measurement technique described in – A Periodic Switching Technique to Compare Receiving Antenna Performance in the Presence of Strong Fading. This is a precise method to compare two receiving antennas with real sky wave signals and the resolution can be less than a decibel. The idea is to switch periodically between two antennas and to estimate their difference on a calibrated graphic strength meter of a SD radio.[…]

Click here to read the full article.

I’ve often assumed height had little effect on the performance of an HF loop antenna–this evaluation seems to support that theory. Thanks for sharing this, Harald!

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Can someone ID this Singer Eaton magnetic loop antenna found on eBay?

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Many thanks to SWLing Post contributor, Dan Robinson, who shares a link to this 31″ Singer Eaton loop antenna found on eBay.

The seller knows nothing about this antenna, but did provide some detailed photos of the connector and product information sticker:

This loop obviously came from US government inventory based on the sticker. It looks to be quite robust and sports one of the balanced antenna connectors found on rigs like the Hammarlund SP-600. I’m guessing this loop might be fixed-frequency as I see no tuning section with a variable capacitor.

Can any SWLing Post readers shed a little light on this loop?  Have you ever used one? Please comment! 

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Using amplified loop antennas with portable radios?

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SWLing Post contributor, Klaus Boecker, sports a homebrew magnetic loop antenna on his balcony in Germany.

Many thanks to SWLing Post contributor, Marty, who writes:

I have a question about loop antennas; specifically which type is “better,” passive magnetic loops or active electric loops?

I know, “It depends.”–?

I live in a ground-floor apartment, with a small porch, lots of RFI and restrictions against visible antennas. Also there are no trees within 75 ft of my porch, which faces on a parking lot. My radio is a Tecsun PL-660, which works okay inside with my 10-ft bare wire antenna hidden on the porch.

With a loop antenna, I’d like to mount the antenna on the porch at night and have a remote tuner/control inside because it’s very hot n humid here in Louisiana even after dark.

No doubt there are a number of magnetic loop antennas that could serve you well in your situation, Marty.

To answer your first question, though, you should search for a wideband amplified loop antenna since you’re only concerned with receiving.

Passive loops are great antennas on the shortwave bands–and easy to build–but they best serve ham radio operators who wish to transmit. Passive loops typically have a very narrow bandwidth that requires the operator to constantly tune the antenna when they tune the radio a few kHz. Most amplified wideband loops need no separate tuning mechanism.

Last year, I posted an article about choosing the right loop antenna for situations like yours where one has limited installation options.

Click here to read : Shortwave antenna options for apartments, flats and condos

Portables and amplified loops?

I do hesitate to encourage you to invest in an amplified loop antenna when your only receiver is a Tecsun PL-660. Some portables don’t handle amplified antennas well–they can easily overload and I imagine you can even damage the front end of the receiver.

I’m well aware, however, that there are a number of readers here who do couple their portable radio to an amplified loop. I have connected a number of portables to large wire antennas and found they could easily handle the extra gain, so I imagine an amplified loop would perform as well; the Sony ICF-SW7600GR, Tecsun S-8800, and Sangean ATS-909X come to mind.

But the PL-660 is a hot little receiver even with the built-in telescopic antenna–I’m not sure if amplification would help or hinder.

Please share your experience

This is where I hope the amazing SWLing Post community can pitch in and help us out here!

Does anyone here regularly connect their PL-660 to an amplified loop antenna? If so, what model of antenna are you using? Are there other portables out there that you regularly connect to amplified loops? Please share your notes, thoughts and experience in the comments section.

Thank you in advance!

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Test the Bonito MegaLoop FX and MegaDipol live on the air

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Many thanks to Dennis Walter with Bonito, who shares the following for anyone interested in the Megaloop FX or MegaDipol::

If anyone like to test the MegaLoop FX live on the air, you can do it here:

http://emeraldsdr.ddns.net:8073/

The MegaDipol can be tested on the same location here:

http://emeraldsdr.ddns.net:8074/

The location of both KiwiSDR receivers is Carlow, Ireland. Both receivers exhibit excellent low noise characteristics.

Indeed, as I publish this post I’m listening to near perfect copy of Radio France International–using the MegaDipol–on 17850 kHz as they report the results of the FIFA Women’s World Cup. (Congratulations team USA!)

Thanks for sharing these links, Dennis!

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