Tuesday, 18 February 2020

Barn Door Wide! Hunting For NDBs In CLE253

This weekend's upcoming CLE event will be the "Barn Door" listening event.

Participants are required to use receivers without the usual narrow filters. Some of the older tube radios can do this easily as can most homebrew receivers ... especially the regens!

If you've never listened to the NDB band with a wide bandwidth, it is a fascinating experience! If conditions are normal, you can typically hear a half dozen or more signals, all at various pitches, vying for your attention. It's almost as if you have plunked yourself down in the middle of the NDB forest of signals, and they are coming at you from all directions.

Many choose to use one of their homebrew receivers for this event, often as simple as a '1AD' or a '1 Active Device' circuit.

From organizer Brian Keyte:

Hello all

Here comes our sixth 'Barn Door' Coordinated Listening Event.
Between us there will be a great variety of ‘Back to Basics’ receiver
types in use.  Maybe this is an opportunity for you to bring back to life
that old receiver that has been collecting dust for so long!

    Days:      Friday 21 to Monday 24 February 2020

    Times:    Start at Midday on Friday 21st, your LOCAL time
                   End at  Midday on Monday 24th, your LOCAL time

    Frequencies:   Centred on 360 kHz (see below)

    NDBs:     NOT MORE than 100 'normal' NDBs including any UNIDs
                    (That is not intended to be a target to reach)

We are all asked to listen with NON-SELECTIVE receivers - i.e. with a WIDE
filter or NO filter.  Your 'barn door' should be open wide so you could hear,
at the same time, any NDBs 2 kHz away on both sides of your receiver
setting -  E.g. NDBs on 348, 349, 350, 351 and 352 kHz with the receiver
set to 350 kHz.
You could listen with:

Whichever you choose, use the same receiver throughout the CLE.
If your choice of receiver includes a waterfall please use only the
audio output for your listening.   You could even cover part of the
screen if there is no other way of stopping or hiding the waterfall.

Unfortunately the use of Pskov – and probably of recordings – is
not appropriate for this CLE.

You choose how wide a RANGE of frequencies you will listen in, CENTRED
ON 360 kHz. You could choose 350-370 kHz , 330-390 kHz, 260-460 kHz, etc.
   (That allows each of us to choose a +/- range with enough NDBs to
    match our equipment's capability.   It will also allow us to compare our
    loggings in the Combined Results, at least around 360 kHz).

Logs should show not more than 100 NDBs please (if more than 100
the harvester program will 'drop' the loggings furthest from 360 kHz).

We’ll summarise everyone's equipment on the first page of the combined
results, so please describe:

The RECEIVER/AERIAL you used and the FILTER(s) selected and,
if homebrew, the number of active devices used, transistor types, etc.

All the usual procedures for making logs apply:

Send your CLE log to NDB List, not in an attachment.

Please show on EVERY LINE of your log:

    # The full date (or Day No.) and UTC (the day changes at 00:00 UTC).
    # kHz - the beacon's nominal published frequency, if known.
    # The Call Ident.

Show those main items FIRST on each line, before other optional details
such as Location, Distance, etc.  Please send your complete log with
CLE253 and FINAL in the Subject line.

Whether you are a first time CLE-er or a regular, always make your log
interesting to everyone by giving your own location and do feel free
to share any comments you have on this unusual event.

Joachim or I will send the usual 'Any More Logs?' email at about 2000 UTC
on Tuesday 25th so that you can check that your log has been found OK.
Make sure your log has arrived on the List at the very latest by 09:00 UTC
on Wednesday 26th February.   

We’ll try to complete making the combined results a day or so later.
However you choose to take part, we hope you will find your 'back to basics'
listening enjoyable and worthwhile.
From:   Brian Keyte  G3SIA          ndbcle'at'gmail.com
Location: Surrey, SE England         (CLE coordinator)

Listening without narrow filters is not going to revolutionise our hobby!
But there ARE some unexpected benefits and advantages:

1. Hearing several beacons on a few adjacent frequencies at the same time
becomes easier as you get practice at recognising them by listening to their
very different audio tones. At first, when listening to a random frequency
setting, you may hear just one or two beacons.  But after listening for a
little while you realise that there are three - - four, maybe more, all of
them audible without altering any of the receiver controls.
It is a skill that gives satisfaction as you improve.

2. Hearing multiple beacons like that can be useful because, with no extra
tools, you can hear NDBs over a wide frequency range much more quickly than usual, perhaps spotting the arrival of new UNIDs or the return of occasional beacons.  (To protect your hearing, keep your receiver gain controls fairly low, except around very quiet frequencies).

3. With normal listening it is easy to miss any NDBs that have abnormal
carrier frequencies or non-standard offsets.  With 'Barn Door' listening
they won't escape because everything is let through.

4. When using a wide filter, you may be surprised by hearing some
Broadcast Station signals (e.g. harmonics) among the NDBs and you will
be able to identify them.

With a narrow filter, often you may not recognise an AM signal as audio
- it just sounds like nondescript 'hash' affecting a wide range of frequencies
around the central carrier.

Maybe listeners will report some other good things about their barn door
listening during the CLE - and probably some bad things too!

Do join in if you can.

These listening events serve several purposes. They:
  • determine, worldwide, which beacons are actually in service and on-the-air so the online database can be kept up-to-date
  • determine, worldwide, which beacons are out-of-service or have gone silent since the last CLE covering this range
  • will indicate the state of propagation conditions at the various participant locations
  • will give you an indication of how well your LF/MF receiving system is working
  • give participants a fun yet challenging activity to keep their listening skills honed
Final details can be found at the NDB List website, and worldwide results, for every participant, will be posted there a few days after the event.

The NDB List Group is a great place to learn more about the 'Art of NDB DXing' or to meet other listeners in your region. There is a lot of good information available there and new members are always very welcome. As well, you can follow the results of other CLE participants from night to night as propagation is always an active topic of discussion.

You need not be an NDB List member to participate in the CLEs and all reports, no matter how small, are of much value to the organizers. 

Remember - 'First-time' logs are always VERY welcome!

Reports may be sent to the NDB List Group or e-mailed to CLE co-ordinator, Brian Keyte (G3SIA), whose address appears above. If you are a member of the group, all final results will also be e-mailed and posted there.

Please ... give the CLE a try ... then let us know what NDB's can be heard from your location! Your report can then be added to the worldwide database to help keep it up-to-date.

Have fun and good hunting!

Monday, 10 February 2020

Loopstick Magic And The CR-1 Clone

BCB Ferrite Loopstick

Regular blog readers may recall my two previous blogs, on the Heathkit CR-1 crystal radio receiver.

This very much sought-after radio is a well engineered ‘double-tuned’ set utilizing a series-tuned antenna tank circuit coupled to a parallel-tuned detector tank.

Both coils are wound on the same 1/4” diameter tubular form containing two ferrite slugs ... one for the antenna coil and one for the detector coil. The coils have been pre-wound and fixed on the form, about 20mm apart while the slugs have been waxed in place to set each inductance to the desired value.

courtesy: Scott's Crystal Radios

I do wish that I'd had enough sense when I was a kid to buy myself a CR-1 as it seemed like they were dirt-cheap.

The $7.95 even included a set of headphones! Of course, $7.95 to a 12 year old was probably a lot of money, being about $70 in today’s currency!

My previous experience with homebrew DX crystal radios (ones that can hear stations other than strong locals) had taught me that they required large coils and ‘hot’ diodes. The CR-1 has neither of these yet it performed exceptionally well during the few weeks of evening tests a few months ago. I was able to log 50 stations, as described in the earlier blog ... and began to see that, just maybe, requirements may not be as rigid as I had always thought, when it comes to building DX sets!

When I discovered several ‘new-in-the bag’ broadcast band ferrite loopsticks in my junk box, I realized there might be an opportunity to allow me to make something very similar to the CR-1 circuit.

These are the same loopsticks used in the crystal ‘Rocket Radio’ of the 50s or in various transistor radios of the day.

I breadboard-mounted the two loopsticks so that the distance between the antenna coil and the detector coil could be adjusted, allowing some control over coupling and selectivity ... something not available with the stationary CR-1 coils.

Using the same antenna, headphones and external wavetraps, proved once again the excellent performance available from a very small and simple hi-Q coil system ... a DX machine without huge coils and expensive Litz! A total of 51 stations were logged over a two-week period, one more than was heard with the CR-1 and with a few ‘almost’ heards still waiting for one of those really good propagation nights. Having the ability to adjust the coupling was very helpful and made some of the weaker stations a little easier to detect. Stations in RED are local strong signals while those in BLUE are skywave propagated DX signals:

Mounting one of my old HRO 'PN' vernier dials on the main tuning capacitor provided plenty of bandspread, with each dial division corresponding to ~ 2kHz. It was very easy to locate any given frequency within the broadcast band once the dial was calibrated.

Soon after, I ran across a post by Zoltan Pap on Facebook’s ‘Crystal Set Radio Group’, describing his unique use of an old 455kHz I.F. transformer in a crystal tuner. I thought this was a rather brilliant idea and dug out an old I.F. can from the junkbox to see what it might offer.

The old I.F. can had two litz-wound (10 strand) tank coils, fixed in place over two adjustable ferrite slug cores ... in reality, something very similar to the, now very difficult to find, ferrite loopsticks used above.

The two inductors measured out at ~ 700uH - 1.1mH as the slugs were tuned from one end to the other. I was aiming for something close to the inductance used in the two CR-1 tank coils ... approximately 380uH.

A sufficient number of turns were removed from both coils to yield the needed inductance and both coils on the CR-1 breadboard clone were replaced with the old I.F. can coils.

In just a few minutes of tuning through the band, it was very easy to hear and separate all 16 local stations (RED in the above log). A few hours after sunset (on a not-so-good night) yielded quick copy of KPOJ (620kHz) in Portland, Oregon (231 miles) as well as CHED (630kHz) in Edmonton, Alberta (534 miles), demonstrating that even this old 1940's I.F. can could be turned into a crystal radio DX machine!

I don't believe the 'Q' of this pair of coils is very high, compared with the smaller loopstick, as its selectivity appears to drop off above 1000kHz. I'll try separating the form into two halves so that the coupling can be adjusted. The experiment is still under way but if you want to play and can't lay your hands on the pricey loopsticks, old I.F. cans are often much easier to find and probably a lot cheaper.

Monday, 3 February 2020

'Barn Door' CLE

The next CLE, coming up at the end of the month, will be another ‘barn-door’ event where listeners are encouraged to use wider bandwidths than normal ... typically something that will allow you to hear beacons at least 2kHz each side of the frequency that you are tuned to.

Your ears will be the only filter that you need!

This will be the first winter event of this type and results could be very interesting! In the past, many participants have used their homebrew regens including the popular ‘1AD’ (1 Active Device) MOSFET regen, built for the NDB part of the spectrum.

The last time this event occurred, I whipped together a 1AD regen in a day which proved amazingly effective in spite of the mid-summer propagation.

There is still plenty of time for you to put something simple together and you can find some helpful suggestions in my previous '1AD' blog here.

I will have more details later, before the event, so please stay tuned and consider getting something ready ... maybe all you need to do is wind a new coil for your favorite regenerative receiver!