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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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23rd Jul 2021, 1:54 pm | #21 | |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
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Re: What is QRP?
Quote:
Morse is mostly keyed carrier wave i.e. the rf is on and off for the periods of the morse characters and sometimes it is generated by audio tones. To get the tone you hear on the receive end, the receiver is tuned around 700 or 800Hz off the transmit frequency. |
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23rd Jul 2021, 3:09 pm | #22 |
Moderator
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Re: What is QRP?
Or you set the Beat Frequency Oscillator (BFO) 800Hz from the IF Frequency (sic).
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23rd Jul 2021, 3:12 pm | #23 |
Dekatron
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Re: What is QRP?
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23rd Jul 2021, 3:17 pm | #24 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: What is QRP?
In some receivers the frequency of the BFO isn't near the IF.
Lawrence. |
23rd Jul 2021, 3:21 pm | #25 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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Re: What is QRP?
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23rd Jul 2021, 3:26 pm | #26 |
Dekatron
Join Date: Apr 2019
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Re: What is QRP?
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23rd Jul 2021, 3:29 pm | #27 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
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Re: What is QRP?
Then there's MCW.
Lawrence. |
23rd Jul 2021, 3:40 pm | #28 |
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Re: What is QRP?
I believe the BFO in the Codar T28 operated at half IF frequency. The IF frequency was odd too, the set using a retuned Mullard Module.
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23rd Jul 2021, 4:56 pm | #29 |
Nonode
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 2,034
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Re: What is QRP?
And for the romantically inclined, 88 is love and kisses 😄. YL is young lady, XYL is the wife. I wonder what ex wife would be - XXYL ?
73 Aub
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23rd Jul 2021, 6:10 pm | #30 | |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,676
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Re: What is QRP?
Quote:
It's the same with "Single Sideband" as that term completely ignores the fact that the carrier is suppressed which arguably is the attribute that sets it apart.
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23rd Jul 2021, 6:13 pm | #31 | |
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Location: Fife, Scotland, UK.
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Re: What is QRP?
Quote:
You want the incoming signal to go right down the middle of the IF passband in order to get he best sensitivity and the best rejection of other frequencies. THEN you want the BFO (or its second harmonic) to be offset from the IF centre by an amount equal to the audio tone you wish to hear the signal as. Different people have different hearing and different preferences, which is one of the reasons for a BFO control (the other one is that on early sets it would have been too costly to try to make it all accurate enough to be fixed) With modern synthesised sets of high accuracy in frequency control, you get the fun of defining what frequency the display should show when demodulating SSB With CW you also have the difference between IF centre and zero beat frequency. David
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23rd Jul 2021, 6:18 pm | #32 | ||
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
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Re: What is QRP?
Quote:
Lawrence. |
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23rd Jul 2021, 6:22 pm | #33 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
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Re: What is QRP?
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23rd Jul 2021, 8:55 pm | #34 |
Heptode
Join Date: Apr 2011
Location: Gosport, Hampshire, UK.
Posts: 597
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Re: What is QRP?
The military in my time used Z Codes and when it was a question, it was preceded by INT.
So INT ZBA meant 'What is the delay'. I only ever used them on teleprinters but the radio operators used them with Morse code as well. Sometimes it took so long to work out what was being said that it may as well just have been sent in English! John
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23rd Jul 2021, 9:17 pm | #35 |
Dekatron
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Location: Wiltshire, UK.
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Re: What is QRP?
One QRP technique that always fascinated me but alas never caught on was 'coherent CW' - an interesting blend of human and 'digital'.
In essence the idea was to use a clock-signal synchronised between the sender and receiver, but locked to the speed of the [manually generated] CW: this clock was used to only unsquelch the receiver when there was a possibility of a 'dot' [or three dots - a dash] having been sent. See https://midnightdesignsolutions.com/ccw/ and http://www.arrl.org/weak-signal-modes Philosophically, I don't see that there's much difference between using a valve/semiconductor amplifier or maths-and-a-computer to improve your weak-signal/low-power communications-efficiency. Last edited by G6Tanuki; 23rd Jul 2021 at 9:31 pm. |
23rd Jul 2021, 9:42 pm | #36 | |
Octode
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,320
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Re: What is QRP?
Quote:
My 10140 kHz QRSS 200mW into a bit of wet string has been spotted as far as Alaska and New Zealand. It's also a great mode to actually clearly see weird stuff on the traces like aircraft reflection, aurora and meteor pings. |
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24th Jul 2021, 12:32 am | #37 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
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Re: What is QRP?
True, but 'in the very beginning' - in my explanation above, I was keeping it as it was originally done before all the good stuff like narrow filters and BFO's etc arrived.
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24th Jul 2021, 3:32 am | #38 | |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
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Re: What is QRP?
Quote:
The American military liked to use "Interrogative" when using fone.
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24th Jul 2021, 5:28 am | #39 | |
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Re: What is QRP?
Quote:
So what's needed for best reception is a cross-correlator looking for dot and dash period pulses as well as for the appropriate space lengths (there is information content in the space lengths and they reinforce the recognition of the pulse periods. An auto-correlator can be used on ordinary CW, but a cross-correlator offers advantages. So the receiving station and the transmitting station need access to high stability frequency references. Short of having a rubidium or caesium standard handy, GPS derived frequency standards were just coming available as CCW was getting interesting. From a communications engineering point of view, Morse sent in A1A at a very regular speed has a comb-like spectrum, and a timing-synchronised receiver can be made to have a comb-like filter characteristic matched to it. A correlator acts as a bank of time-offset filters and tells you which offset best fits the signal. In the end, with the receiver closely matched to the signal, the receiver bandwidth is just enough for the information rate of the message content. Matched filtering is fascinating. Random jitter in the propagation delay, especially with ionospheric propagation modes becomes a limitation, spreading the comb components and requiring less optimal RX bandwidth. David
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24th Jul 2021, 5:29 pm | #40 | |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 690
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Re: What is QRP?
Quote:
I think the difference is a few billion transistors - 2.6 billion in an Intel I7 alone!
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