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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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13th Nov 2020, 9:10 pm | #1 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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A3J mode ?
My AEL3030 is designed as a SSB transceiver but provides an option for A3J mode - which the manual describes as "Compatible AM".
This involves unbalancing the balanced-modulator, which then generates DSB with a residual carrier. The signal then goes through the standard SSB filter-chain which removes either the upper or lower sideband according to the USB/LSB switch setting. It has the advantages over 'classic' DSB-and-full-carrier AM that it only uses half the bandwidth, and allows the RF energy of the audio component to be concentrated into the one active sideband rather than divided between the two. Question: would this be considered acceptable in traditionally-AM nets [like the VMARS 3615KHz one?] |
13th Nov 2020, 10:08 pm | #2 |
Pentode
Join Date: Nov 2018
Location: Freckleton, Lancashire, UK.
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Re: A3J mode ?
As I recall A3J meant SSB either upper or lower
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13th Nov 2020, 10:10 pm | #3 |
Nonode
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
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Re: A3J mode ?
Yes, but carrier suppression is not necessarily implied
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13th Nov 2020, 10:15 pm | #4 |
Moderator
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Re: A3J mode ?
The carrier frequency is likely to be a bit down the slope of the SSB filter, so the rtio of your carrier power to total sideband power may be a bit down on full-fat AM. You might get some comments on lack of punchy audio due to the effect on the efficiency of receiver detectors, along with foxing their AGC a bit.
Interesting to see how many would notice.... If that isn't incitement, I don't know what is. I had a Redifon GK203 exciter in the eighties with all sorts of AM/SSB modes with full, suppressed and reduced carrier. It was fun experimenting. David
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13th Nov 2020, 10:49 pm | #5 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
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Re: A3J mode ?
I thought it was. A3J (or J3A) = SSB (USB or LSB) carrier suppressed A3H (or H3E) Same as above with full carrier The classes for emission designations for DSB SC and ISB SC have always eluded me.
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13th Nov 2020, 11:09 pm | #6 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
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Re: A3J mode ?
As I understand it, A3J is standard SSB. And as such it would not be at all welcome on any standard AM net. No-one struggling with any of the vintage AM receivers will want - or even bother - to try and resolve your signal. From experience, it can take 10 - 20 seconds on a good day to resolve SSB on a classic AM receiver, by which time your over may well have ended (unless you are one of those dreaded "natterers"!)
I wonder if you and others are actually thinking of A3H - which is AM with only one sideband, or SSB with full carrier. Here is some info about A3H which I found on the net: "A3H is defined by the International Radio Consultative Committee (CCIR) as a single sideband emission in which the carrier is 6 dB below the peak envelope power (PEP) . It is also called single sideband- full carrier, because the carrier power is equal to that of a standard AM signal. In most transmitters, an A3H signal is produced by first producing a single sideband-suppressed carrier signal. Then the carrier signal is added. In the case of A3H, the carrier amplitude equals the sideband amplitude. An A3H signal can be demodulated in two ways. In a single sideband receiver, product detection is used. However, it can also be demodulated in a standard AM receiver, using envelope detection. A little care must be taken, though. At 100% modulation, up to 24% distortion results from envelope detection of an A3H signal. Reducing the percentage of modulation reduces the distortion, but has the effect of reducing signal power." Doesn't sound too good, does it. I wouldn't rate an AM signal with near 24% distortion on any net! Richard |
14th Nov 2020, 12:35 am | #7 |
Moderator
Join Date: Mar 2012
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Re: A3J mode ?
Band conditions get blamed for an awful lot
People on a local net did suss that there was something odd. For longer distance contacts the loss of signal made it uncompetitive. I had it, so I had to try it, but I had no reason to try very hard. I only had a 10W PEP power amplifier I'd built for the Redifon. The biggest thing I learned from that setup (RA117 on receive) was how painful netting a decadic knobs synthesiser was. David
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14th Nov 2020, 5:55 pm | #8 |
Pentode
Join Date: Dec 2011
Location: Camberley, Surrey, UK.
Posts: 145
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Re: A3J mode ?
A3J is SSB Suppressed Carrier. The attached chart from Redifon (when they were called Rediffusion Radio Systems) may be of interest.
Going back to the original question I cannot see why a compatible AM SSB signal (A3H) should not be welcomed on a VMARS AM net as many vintage military radios generated AM in this way. I went on such a net some years ago with my Racal PRM4031 which is compatible AM. Peter |
14th Nov 2020, 6:15 pm | #9 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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Re: A3J mode ?
The AEL3030 manual describes its "Compatible AM" operation as A3J in one place and A3H in another; I wonder if they mis-typed something back in the 1970s?
It implements "Compatible AM" by injecting DC and so unbalancing the usual SSB balanced-modulator [which uses a classic MC1496 IC whose implementation is a classic Motorola Application-Notes circuit] but the resultant signal then passes through the rest of the USB/LSB-switch-selectable filter-chain. So I'm assuming only one sideband plus whatever-carrier-makes-it-to-the-output will be radiated. That would be A3H. To me this 'compatible AM' feels a lot more like the pilot-tone-SSB that was trialed by various businesses [including Pye] back in the 80s, as a way to fit more audio-channels into the congested VHF PMR allocation. That depended on PLLs that would lock to the pilot-tone and so avoid the need for a 'clarifier' control, whose operation would have been beyond the competence of the average taxi- or council-roads-crew driver. Last edited by G6Tanuki; 14th Nov 2020 at 6:28 pm. |
14th Nov 2020, 7:44 pm | #10 | |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
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Re: A3J mode ?
Quote:
I think A3H would indeed be fine on a net containing classic AM receivers, with (usually) a diode detector, and SSB mode. I rather doubt though whether A3H is as common as you think. The PRM4031 is certainly one example - but as far as I recall is something of a rarity. I checked out the Clansman PRC-320 - and I was surprised to see that its AM is real AM (A3) with carrier plus both sidebands. What other sets do you have in mind that generate A3H, and could be given the label "vintage"? Richard |
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14th Nov 2020, 11:06 pm | #11 | |
Pentode
Join Date: Dec 2011
Location: Camberley, Surrey, UK.
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Re: A3J mode ?
Quote:
And lets not forget that VMARS is "Vintage and Military Amateur Radio Society" so even if not vintage they are definitely military. Last edited by PeterRoberts; 14th Nov 2020 at 11:16 pm. Reason: added missing word |
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14th Nov 2020, 11:47 pm | #12 | ||
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,724
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Re: A3J mode ?
Quote:
There is a "carrier" control on the back that basically unbalances the balanced modulator in the AM and CW modes, but the xtal filter remains in circuit. On the rare QSO I had with this mode I would have logged it as "A3", it wouldn't have occurred to me to put A3H. Just don't tell OFCOM/RA/HO/MPT/GPO about my inept record keeping.
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15th Nov 2020, 12:10 am | #13 | ||
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
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Re: A3J mode ?
Quote:
Definitely military? Well, I have them listed in my own library as "commercial". The TRA-931 was evaluated by the British Army and rejected as being not robust enough. The fact that some military forces bought some of these sets could make them arguably military - but then Pye made commercial sets, which the Army bought - that doesn't make the sets "military" - just commercial sets used by the military. However this is beside the point. None of these sets are what I would call "common" - like say a WS19, a R107, a T1154, or any of the other classic amateur sets that produce full AM. I listened to the VMARS net for many years - and those sets you list with compatible AM were unusual - but not a problem, because the noise/interference level on 3615kHz made the risk of 24% distortion academic! My original comment is that SSB - A3J - is unwelcome on any net that is predominantly aimed at traditional AM sets with diode detector receivers. Sure, those who can just switch to SSB will do so - but that is not an easy option on sets that need main tuning, BFO tuning and RF gain all adjusted accurately. Richard |
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22nd Nov 2020, 1:56 pm | #14 |
Triode
Join Date: Mar 2015
Location: Nottingham, Notts. UK.
Posts: 19
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Re: A3J mode ?
A3J every common to marine sets , The only complaint when on a A3J set such as my SEG 15D was that it could do with some more mod .There is a suppressed carrier mode A3A which has -60 db carrier ssb mode so that it can be received on am only receiver .Pure AM will be better but not a show stopper on am nets, stay safe in these times and enjoy your time on the radio Graham G1DNZ
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24th Nov 2020, 2:19 pm | #15 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,654
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Re: A3J mode ?
A3A mode is SSB with carrier at -16dB, i.e.a pilot tone. That won't be compatible with a standard AM receiver, but it would allow automatic carrier reinsertion, with phase locking to the pilot.
The -60dB carrier version (not A3A) is SSB, ie. A3J! Presumably that was a typo! "Pure AM" (A3) is exactly what the AM nets expect - its these mangled modes that are less welcome. Richard |