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When discussing signal levels and power output, hams like to say things like:

Using higher power isn’t important because it only gives you one additional S unit

and

You’ll lose some power in the coax but you won’t even notice a few dB

These statements are often true and at the same time may be completely wrong. I’ve noticed that radio amateurs pushing the limits of their station pay close attention to every decibel they gain or lose. This is especially true at VHF/UHF frequencies where signals may be weak. A dB here, a dB there, the next thing you know it adds up to something big!

Definitions

First, let’s make sure we have a few definitions right. The decibel (dB) is defined as the ratio of two power levels:

dB = 10 log (P2/P1)

One decibel corresponds to a 26% increase in power level. A well-known rule of thumb is that doubling the power corresponds to a 3 dB increase. Similarly, chopping the power in half drops the signal level by 3 dB.  A 10 times increase in power is 10 dB. (Voltage can also be used to calculate decibel relationships but to keep it simple, I’ll just use power.)

The S Unit is normally defined as a 6-dB change in signal level, which is a factor of 4 in power. (Your S meter may or may not actually follow this rule but that is a topic for another day.)

Power Level

Let’s compare a few different power levels to get a feel for how decibels and S units behave. Let’s use a 5 watt QRP level as our reference power. If we crank up the power to 100 watts, we  have 10 log (100/5) = 13 dB increase in power level. This is slightly more than two S units (2 x 6 dB), so we would expect the S meter on the other end to read 2 units higher.

Now suppose we kick in our linear amplifier to produce a 1 kilowatt RF signal. This power level is 10 log (1000/5) = 23 dB higher than the 5 watt signal, or roughly four S units.

Now if our QRP signal was a solid S9 to start with, adding another 23 dB on top of it may not be that significant. The station can be heard at S9 or can be heard even louder at S9 + 23 dB. Except when there’s a pile of stations all calling that rare DX…then the loudest station tends to be heard. Crafty operating skill and good luck may overcome the power difference.

But consider the other extreme. Our QRP station is being heard right at the noise floor on the receive end. The two stations are struggling to complete the contact and the propagation path degrades by 2 dB. Now the QRP station is below the noise and uncopyable. We increase our power to 100 watts and gain 2 S units…still not very strong but the ability to receive the signal improves dramatically. Crank it up to 1000 watts and you gain another couple of S units and the copy is quite good. The key point is that changes in signal level matter most at the margin, when you can just barely copy the signal. (By the way, there is nothing wrong with running QRP…many ops enjoy the challenge of making contacts with low power.)

At the receiver, our ability to recover the signal is determined by the signal-to-noise ratio (SNR). A higher noise floor at the receiver means it will be more difficult to hear the signal coming in. The type of modulation being used may also make a big difference. Good old CW and the WSJT modes use a narrower bandwidth and will get through when wider-band modulation (SSB, FM) fails. In all cases, a stronger signal works better.

Antennas

Antenna systems also increase our signal level…and they do it for both transmit and receive. I recently did some comparisons of VHF antennas from a SOTA summit. My 2m Yagi antenna has 6 dB of gain (referenced to a dipole) and my comparisons showed that the performance of this antenna was good enough to pull some signals out of the noise to be solid copy. This occurred when the other station’s signal was right at the noise floor (using my lower gain antennas) such that the 6 dB improvement had a significant impact.

Sometimes hams will say that VHF is just line-of-sight propagation and that the signal level doesn’t matter much. This is partially true but often we are stretching for contacts beyond line-of-sight. Take a look at this article: The Myth of VHF Line-Of-Sight. This is another case where we are operating on the margin and every dB matters.

Feedline loss can cause us to lose decibels, which impacts both transmit and receive performance. If your coaxial cable is short, then the losses may be negligible. Increasing cable length and increasing frequency produce more loss. For example, 100 feet of RG-8X has only 1.1 dB of loss at 10 MHz. Increase the frequency to 146 MHz and the loss jumps to 4.5 dB, using the Times Microwave cable calculator. That means 50 watts of power at the transmitter turns into 17.7 watts at the other end of the cable. Using LMR-400 coax reduces the attenuation to 1.5 dB.

Summary

You can choose to ignore small changes in your signal level. A dB here or there may not make a big difference with casual ham radio operating. But these losses tend to add up and may become significant. Most importantly, just a few dB may be the critical difference between making a radio contact or not, when operating at the margin.

The post A Decibel Is Still A Decibel appeared first on The KØNR Radio Site.

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Extra Class Exam Questions – Part 15.
E4A Test equipment: analog and digital instruments, spectrum analyzers, antenna analyzers, oscilloscopes, RF measurements, computer-aided measurements.
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LF-336kHz courtesy: http://www.ve3gop.com/

It's CLE time! 'CLE's are 'Co-ordinated  Listening Events, and NDB DXers around the world focus their listening time on one small slice of  the NDB spectrum.

Propagation on MF has been both hot and cold for the past few weeks, seemingly depending on where you live and the amount of geomagnetic activity affecting your region. As well, the Sun has been throwing a lot of Coronal Hole Streams toward earth which may or may not affect this weekend's propagation ... but this is all part of the radio-magic fun.

A 'challenge target' for listeners in North America is LF - 336kHz in La Salle, Manitoba, in the southern central part of the province. Even though running just 50 watts, it's widely heard throughout North America and is a good target for listeners everywhere. Listen for LF's upper sideband on 336.390 kHz.

When tuning for NDBs, put your receiver in the CW mode and listen for the NDB's CW identifier, repeated every few seconds. Listen for U.S. NDB identifiers approximately 1 kHz higher or lower than the published transmitted frequency since these beacons are modulated with a 1020 Hz tone approximately.

For example, 'AA' near Fargo, ND, transmits on 365 kHz and its upper sideband CW identifier is tuned at 366.025 kHz while its lower sideband CW ident can be tuned at 363.946 kHz. Its USB tone is actually 1025 Hz while its LSB tone is 1054 Hz.

Often, one sideband will be much stronger than the other so if you don't hear the first one, try listening on the other sideband.

Canadian NDBs normally have an USB tone only, usually very close to 400 Hz. They also have a long dash (keydown) following the CW identifier.

All NDBs heard in North America will be listed in the RNA database (updated daily) while those heard in Europe may be found in the REU database. Beacons heard outside of these regions will be found in the RWW database. These databases have recently been re-vamped and are slicker than ever before!

From CLE coordinator Brian Keyte (G3SIA), comes the following CLE info:

 Hello all,

Our sixth special 'Channels Challenge' listening event is nearly here.
These are the full details.

    Days:      Friday 28 May - Monday 31 May
    Times:     Start and end at midday, your LOCAL time
    Range:     275 kHz - 425 kHz   (see below)
    Target:    Try to log ANY ONE NDB in each channel

The main challenge is to try and log ONE NDB in each of the
151 channels in the range from 275 kHz up to 425 kHz inclusive.
The last time we did this was in CLE248 in September 2019.

The 'channel' means the NDB's NOMINAL (published) frequency.
(It may not be quite where you hear the Morse ident of course). 
In parts of the World some NDBs are on intermediate frequencies,
such as 321.5 kHz.  Logging an NDB on a 'half frequency' would be OK.
  E.g. OK for channel 321 would be  EITHER  one on 321.0 kHz
                OR  one on 321.5 (shown as 321.5 in your log of course).

Each NDB must be a 'normal' one - no DGPS, NAVTEX or amateur.
(If you hear any UNIDs, please show them in a separate list).

So it means a highest possible total of 151 CLE loggings in all - and that
will surely be impossible for everyone!

If you have extra time and want to make the challenge more interesting you
could include NDBs which:

   Give you the greatest number of DIFFERENT RADIO COUNTRIES heard.
   (See our Countries list at
http://www.ndblist.info/beacons/countrylist.pdf

 
    Each State/Province in USA, CAN and AUS is a separate radio country)
   OR  give the greatest TOTAL DISTANCE from you to all of the NDBs.
   OR  include the greatest number of MIDDAY LOGGINGS
          i.e. heard within 2 hours of midday by your local clock time.

Send your 'Final' CLE log to the List, ideally as a plain text email (not in
an attachment) and, IMPORTANT, with CLE268 and FINAL at the start of its
title.
Please show on EVERY LINE of your log:

   #   The full date or day no.  e.g. '2021-05-29' or just '29', etc.
          and UTC (the day changes at 00:00 UTC).
   #   kHz  - the beacon's nominal published frequency.
   #   The Call Ident.

Show those main items FIRST on every line, before other optional details
such as Location, Distance, Offsets, Cycle times, etc.

Tell us your location of course and details of your receiver, aerial, etc.

We will send the usual 'Any More Logs?' email at about 19:00 UTC on Tuesday
so you can check that we have received your log OK.
Do make sure that your log has arrived on the List at the very latest by
08:00 UTC on Wednesday 2 June.
We'll try to complete making the combined results within a day or two.

Good hunting,
   Brian and Joachim
-------------------------------------------------------------------
From:      Brian Keyte G3SIA       [email protected]
Location:  Surrey,  SE England      (CLE coordinator)
-------------------------------------------------------------------

(Reminder:   You could use any ONE remote receiver for your loggings,
stating its location and owner - with their permission if required.
A remote listener may NOT also use another receiver, whether local or
remote, to obtain further loggings for the same CLE).

If you are interested in some remote listening - maybe due to local difficulties - you could use any one remote receiver for your loggings, stating its location and with the owner's permission if required.( e.g. see  kiwisdr.com ) A remote listener may NOT also use another receiver, local or remote, to make more loggings for the same CLE.

These listening events serve several purposes. They

Hello and welcome to the 414th installment of Linux in the Ham Shack. In this episode, the hosts discuss the Young Ham of the Year Award, new EM exposure limits in the UK, privacy at the FCC, the impending demise of Freenode, expensive keyboards, medical device hackers, wfview, js8call and much more. Thank you for listening and have a fantastic week.

73 de The LHS Crew

In this episode, Martin (M1MRB) is joined by Leslie Butterfield G0CIB, Dan Romanchik KB6NU and Edmund Spicer M0MNG to discuss the latest Amateur / Ham Radio news. Colin (M6BOY) rounds up the news in brief and in the episode we feature we discuss the RSGB Survey with the New RSGB President.

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