Gil you must have good ears for SSB. I could not hear OH at ALL. The MW0DEW I could HEAR but not understand even ONE word! On CW that would have been easy. I can copy CW up to -13dB SNR, though with repeats. -10dB SNR no sweat at all. But SSB I have always been poor at, like all things is needs training I guess. Does that radio do CW too? Lovely radio... need to look out for that sort of gear.
QuoteDoes that radio do CW too? Lovely radio...
Sure does, without keyer of course, but there is a neat little Morse key that goes with it. The only issue is that the CW tone is 2kHz. It does have a good 250Hz filter though.
Gil.
Well that's great! I could put up with the 2kHz CW tone I guess, that's just for outgoing? You can vary the pitch of incoming CW or is that on frequency also when pitch is at 2kHz? Maybe the logic there was if anyone heard you they might think they're having tinnitus. Or, in the battle field, perhaps that pitch gets above the noise of explosions and the shriek of missiles?!
2kHz is what you hear. The guy on the other end, of course will set your tone to what he uses...
Gil.
Quote from: gil on August 23, 2017, 12:18:22 PM
2kHz is what you hear. The guy on the other end, of course will set your tone to what he uses...
Gil.
You misunderstood my question :) the local side tone is 2kHz. But what of your receiver when you are zero beat with the station, do you have to listen to them at 2kHz also, or is there BFO or a different lesser TX/RX offset? The local side tone at 2kHz I could live with but always listening to signals that are on frequency, at 2kHz, I think that would be more difficult.
Yes, you listen to them at 2kHz.
Gil
Sent from my SM-G928F using Tapatalk
Interesting but it's OK. Any idea WHY it is 2kHz and not 1kHz? It may have something to do with using it on either SSB or CW? To create good interopability between the 2 modes but reduce cross QRM a little.
Did wonder what the working conditions were of both stations and if you have made a ssb contact since. Larry
QuoteAny idea WHY it is 2kHz and not 1kHz?
I have wondered about this too... I don't know. The dialed-in frequency is always 2kHz above what we are used to. Ex: If you want to listen to 14300, you must dial in 14302, when using USB. For CW and AM you dial in your frequency as usual, no offset.
QuoteDid wonder what the working conditions were of both stations and if you have made a ssb contact since. Larry
Not yet. It was on 20m, late afternoon. Distance is 1273 miles. Julian is above 65deg North, I'm at 50.7, so it's quite a bit North...
Gil.
OK now I understand. I have the answer to why that is!
IN SSB (USB) the 14302 is not the carrier suppressed frequency that radio amateurs generally use, but it is the centre of SSB transmission. Well, it's not the real centre which may be closer to 1.5kHz and is generally used in commercial non-military services. Example: 14300 USB the SSB is spread out from 14300 to 14303, 3kHz wide. So it makes sense (and avoids confusion that radio amateurs constantly suffer from where SSB causes QRM to CW as they do not understand this issue!) to instead call that frequency 14301.5 or, for simlicity, rounded off, 14302. So with your radio there they have decided to make it 2kHz above the suppressed carrier frequency. Brilliant. And for CW, if you transmit on 14302 or even 14301 you will be heard by those stations on SSB at a 2kHz or 1kHz pitch. They have clearly opted for 2kHz. This way you can also easily zero beat CW station at 2kHz. They could have chosen 1kHz but for whatever reason, chose 2kHz. Maybe because rounding 1.5kHz (the standard ITU non-amatuer way to define an SSB frequency, e.g. LSB would be 14298.5, USB would be 14301.5) is done upward when equidistant mathematically by convention, hence 2 rather than 1.
They wanted to avoid .5 in the 1.5 for reasons of simplicity and speed and efficiency, this is the military! Another reason to choose 2 rather than 1kHz in this case, is the pitch. 2kHz CW causes less QRM to USB than 1kHz in the audio pass-band. Also for CW. If you are on 14302 CW you will get less QRM from the 14302 SSB (actually 14300 USB suppressed carrier frequency) than you would if it were 14301USB. Now it all makes sense. Quite clever. Just you have to suffer the 2kHz pitch :D because for the military your COMFORT is not their concern, avoiding problems (as above described and suffered by radio amateurs trying to do cross mode without understanding it) is their concern.
This was also the thinking between an SSB and CW frequency some of us chose for a net. The two are "2 kHz" apart, exactly that is if you use the SSB suppressed carrier frequency display and the CW transmit frequency display.
It's a military rig so here's my guess. We hear best between 2KHz and 4KHz. Our hearing is about 10dB worse at 700Hz(some charts say it's a smaller difference). Also, I'm guessing in a loud battle environment, or driving in a jeep or tank, there's going to be a lot of low frequency noise and less up in the 2KHz range.
(http://i120.photobucket.com/albums/o170/cockpitbob/a10_sensitivity_zpsnuewbaud.gif)
LOL, I was typing my reply while swxx posted his. swxx makes some great, insightful points! I agree with him. It makes a lot of things simple, and in battle simple works best. I think the fact we hear better at 2KHz than 700Hz is just icing on the cake.
Excellent info cockpitbob! That's the value of sharing here on these great forums. So many reasons then to choose the 2kHz in those RT320's. For CW operators the reason they like low tones is it is EASIER on the ears over a long duration AND easier to separate closely spaced signals. But indeed, at any distance from the radio and with normal background noises let along motors running, 2kHz gets through your house and down the road much clearer than 600Hz! I notice this when leaving receiver on in a wide filter. High pitches get through to other rooms much easier and clearer at the same volume. Thanks for posting this very helpful chart.
Mil HF manpacks from that era which MIGHT be used for special operations had the high sidetone for highspeed Morse burst. The common 'burster' in the US inventory was the AN/GRA-71.
(http://www.radiomilitari.com/gra71-1.jpg)
Morse message was loaded in using an 'encoder' that had a wheel with letters around it's periphery, which loaded the keying information onto magnetic tape. At sked time the tape was loaded onto the actual burst keyer, the spring wound-up and when ready and IDY (tuning pulses) were sent for the outstation to tune to and then BHzzzzzziP! the burst went out.
These were the days of magnetic tape recorders and to get a usable tone at the other end after slowing the Morse down twenty time to 15 groups per minute, you ended up with a 100 Hz tone, which is low , but doable.
Wow so true I had forgotten about the burst CW, excellent info Radio Ray! These days wide band RX can pick up everything for later analysis so this would not be so secret but back then unless one knew in advance the time and frequency it'd have been nigh impossible to capture transmission by enemy. I know a former submarine CW OP and that's exactly what he used to do, they'd surface, send the burst, and dive again.