Category Archives: Accessories

FM Notch Filter for SDRPlay RSP1

RF filters are used (as the name implies) to filter/remove the frequencies you are not interested in and/or let frequencies you want pass . They come in lots of types. For example a band-pass filter lets the signals in a frequency range to pass through it and rejects/attenuates other frequencies. The opposite of band-pass filter is a band-reject or band-stop filter (also called a notch filter) which rejects/attenuates signals in a specific range and lets other frequencies get through the filter. Lots of different filters are used in SDRs and traditional radios. For example AM low-pass filters (only let frequencies lower than 1.7MHZ or so pass) or band-pass filters for various ham radio bands.

One of the popular use cases for a notch filter is in the FM broadcast range (88-108 MHZ in most parts of the world)

When you live near a powerful transmitter, it can affect the operation of your receiver in other near frequencies (or overload your receiver’s front-end), but I didn’t want the notch filter for this reason. I’ve got a SDRPlay RSP1 (among many other SDRs) which due to its architecture, has some images of FM band in the UHF range (for example in 330-350 MHZ). In fact they’re the images of the product of LO harmonics and FM frequencies.

You can temporarily move/shift the frequency by changing the LO frequency which does not remove them, but moves them around.

Another method to remove these images is using a band-stop filter.

This is the filter I’m using (Thanks to my friend Amirhosein Hasanpur who designed and built it):

Here you can see the effect of using a FM notch filter on my SDRPlay RSP1:

FM, without filter:

FM, with filter:

UHF (images) without filter:

UHF (images) with filter:

Here’s a link to a Zip file containing the PCB (in Protel), schematics (pdf) and S Parameters (pdf):

https://www.dropbox.com/s/l98kylrofohgqxf/SWLing.zip?dl=0

Note: Like any other SDR test/review, the results depend on lots of different parameters (various gain values, LNA, antenna, software, etc). These pictures are captured with the same conditions just to show the effectiveness of this filter and your milage will definitely vary, but expect a similar outcome. If you live close to a powerful transmitter or use LNAs, you will receive some signals, even when using the filter.

Final note: this issue is solved in the newer version of SDRPlay (RSP2) : it has software-selectable notch filters for FM and MW broadcast frequencies.

Mehdi Asgari, the author of this post, is a regular contributor to the SWLing Post. Mehdi lives in Tehran and is an active member of the EP2C amateur radio club.

Panasonic RF-2200: Mario spots the model RD-9820 matching coupler

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

This antenna coupler was the companion for the RF-2200, they come up once in a while on eBay. Just some radio memorabilia/trivia to store away in the SWL file of brain hihi.

Click here to view on eBay.

Thank you, Mario! Until last year or so, I wasn’t aware the RF-220 had a matching coupler. I’m sure radio collectors would jump on one of these in good condition. It’s a lot to pay for a simple coupler, though this seller appears to accept best offers.

The great thing about eBay is if you’re looking for something rare and are willing to pay for it, the world is your oyster.

On the other hand, there’s exactly what Mario implies: many of us find eBay to be an amazing resource for discovering rare radio items, tucking them away in the dark recesses of our radio brains, which then helps us spot them when they pop up at local hamfests, swap meets, yard sales or thrift stores!

Southgate ARC: What Is a Balun and How to Make One Cheaply

(Source: Southgate ARC)

Ham Radio – What Is a Balun and How to Make One Cheaply

A Balun is a transformer which allows coaxial cable, which is an unbalanced lead to be connected to a balanced load, for example a resonant aerial.

The 1:1 balun is often called a choke balun, it works by eliminating Radio Frequency currents flowing on the outside of your coaxial cable, this is important because it prevents the pattern of the dipole becoming distorted and prevents the braid of the coaxial cable radiating.

Connecting coax to your resonant dipole which can be configured in a V shape or in a sloping fashion, however serious power loss and feeder radiation can occur without the use of a balun transformer. No one wants to induce Radio Frequency currents into Television receivers or Broadcast equipment as it may result in disputes with neighbours and could possibly lead to your station having to close down. Try to keep the centre of your aerial away from buildings as it may induce Radio currents into the mains wiring.

Building a choke is not difficult all you need is some plastic pipe available from many Do It Yourself outlets and warehouses. I use a length of about 1 foot of plastic pipe and 21 feet of coaxial cable, the length of the pipe and diameter is chosen because it works well if using R-G-5-8 coax the ends of the pipe can be sealed after placing a SO-239 connector for your coaxial lead. I use two bolts and solder tags at the other end of the pipe to connect the ends of the dipole to the choke.

When wrapping your coax around the pipe don’t use too much force as it may damage the inner braid and space the turns away from each other by a millimetre or two. R-G-2-1-3 coax around 21 feet used with 5 inch pipe will handle 400 watts pf power. Wire ties can be used to hold the turns together along the length of the pipe. Using these measurements your choke will cover all of the ham radio bands from 1.8 Megahertz through to 28 Megahertz and will keep the radiation pattern.

Using a dummy load connected to the choke and transmitting 100 watts from my transmitter indicated an S.W.R. readings of around 1.5 to 1 at 3.5 Megahertz when testing 28 Megahertz the S.W.R. reading came down to 1.1 to 1 which is an excellent match. Using the choke as it should be at the feed point of a dipole cut for 40 metres give an S.W.R. reading of 1.2 to 1. The highest reading was 1.5 to 1 when using 18 Megahertz but the rest of the High frequency bands gave me very acceptable matching.

By
John Allsopp G4YDM
https://g4ydm.blogspot.co.uk/

Article Source:
http://EzineArticles.com/expert/John_Allsopp/1925417

Article Source:
http://EzineArticles.com/9615600

Radio Wall Clocks: Mario’s eBay find

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

Hi Thomas,

These have been popping up on eBay, reasonable price, with face markings just like an old shortwave radio dial.

Click here to view Zenith wall clock.

Pretty nice gift for the SWL who has everything!

Click here to view Sparton wall clock.

Have a good day and weekend!

Thank you, Mario! Those are nice clocks and, as you say, rather affordable at $26.49 shipped! I like the fact they also include 24 hour markings.

Your message lead me down a path to search eBay for other radio wall clocks. There are hundreds out there! I found that searching with the term “ham radio wall clock” seemed to work best.

WRTH 2017: A look inside

I received my copy of the 2017 World Radio and TV Handbook (WRTH) directly from the publisher last week, just prior to Christmas holiday ravels. As I mention every year, I look forward to receiving this excellent staple radio reference guide–and this is their 71st edition!

WRTH’s team of noted DXers from around the world curate frequencies and broadcaster information by region; while I’m not sure how they orchestrate all of this, the end result is truly a symphony of radio information. In addition to broadcaster listings, WRTH’s radio reviews, feature articles, and annual HF report make for excellent reading.

But the WRTH isn’t just a frequency guide: the publication always devotes the first sixty or so pages to articles relating to various aspects of the radio hobby. Following, I offer a quick overview of these.

The first article always features a WRTH contributor:  this year, WRTH’s International Editor, Sean Gilbert, tells us what sparked his interested in the hobby and what lead to his career with WRTH which started in 2000.

The second set of articles is always my favorite: WRTH receiver reviews.

This year, WRTH begins with a review of the Icom IC-7300 general coverage transceiver.  They also review the Reuter Elektronik RDR55D, and re-visit the SDRplay RSP1. Following radio reviews, they evaluate the excellent Wellbrook ALA1530LNP magnetic loop antenna and the Bonito AAS300 3 way active RF splitter.

The following article focuses on one of my favorite shortwave broadcasters, The Mighty KBC. WRTH contributor, Max van Arnhem traces the broadcaster’s history and gives us a little insight about the people behind this music powerhouse. If you’re a KBC fan, you’re in for a treat!

I was very happy to find that the following feature article explores the world of Remote Reception. No doubt, remote listening is becoming one the most accessible ways many of us discover and enjoy our hobby today–especially as it can be difficult for some of us to fight urban radio interference.

Following this, WRTH writer, Hans Johnson, features an article on CKZN St. John’s Newfoundland.  In this short article, Johnson covers the history and mission of this shortwave relay, dating back to the days when Newfoundland was a British dominion. Looking forward, Johnson notes that the CBC intend to not only continue this service directed at Labrador’s most remote areas, but it intends to replace their 1 kW Elcom Bauer transmitter in the coming years. This pleases me to no end as I’ve always loved snagging this particular relay of CFGB from my home here in North Carolina.

Next, DXer Rob Shepard writes about his travels in South America and the Pacific. Being an avid traveller myself, I love reading about others’ adventures across the globe with radio. Shepard even notes some catches from the Queen Mary II. I’ve never had the chance to do DXing while maritime mobile, but I hope to someday.

The following article features Danish radio enthusiast, Vagn Fentz, who has collaborated with WRTH since one of its very first editions. His radio history starts back when he was a schoolboy in Denmark during WWII, listening to the radio in secret. His story gives us insight into both his own world and that of the WRTH over the years.

Next, Michael Pütz outlines the progress, so far, of setting up an HF disaster relief radio network: the IRDR Project. If you haven’t heard of the IRDR project, this article makes for a great primer and also speaks to the potential future of a radio network that could have major positive impact over vast regions in the wake of disaster.

The final article–a tradition–is the WRTH  HF propagation report/forecast by Ulf-Peter Hoppe. Always an informative read (despite the fact we’re heading into a solar minimum).

The 71st is another fantastic edition of the World Radio TV Handbook. I’ve never been disappointed with WRTH, in truth. Their publishing standards are such that the quality of their reviews, their writing, and (most importantly) their broadcast listings are simply unparalleled.

For DXers who collect QSL cards, you’ll find that broadcaster contact information in WRTH is often more up-to-date than a broadcaster’s own website. When readers contact me asking for QSL information from an obscure broadcaster, the first place I search is the current WRTH. Remember: their information is based on volunteer contributors who specialize in specific regions of the world–the most knowledgeable regional DXers keep this publication accurate.

Purchase your copy of WRTH 2017 directly from WRTH’s publishers, or from a distributor like Universal Radio (US) and Amazon.com (US), Radio HF (Canada), or BookDepository.com (International).