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USB + Carrier AM




 
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Author Topic: USB + Carrier AM  (Read 869 times)
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KA3EKH
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« on: March 19, 2018, 11:01:01 AM »

I have moved out of the WW2 stuff years ago had ART-13 and built up a TBW transmitter and used that for several years mostly on 7290 along with doing several TCS and command sets but found that unless you were running high power AM it was a waste of time, at least for me. Running a TCS developing a whopping five watts or so resulted in lots of unanswered CQ or no responses when returning others calls. Moved to radios developing at least 100 watts and the problem went away.
Has nothing to do with this but spent some time stomping on 160 (1885) running a converted RCA Broadcast transmitter at 375 watts and would always have issues talking with stations who would answer my CQ running some piss week Yeasu/Icom  rig struggling to make 25 watts of AM, life is too short for QRP.
The last couple years I have been playing around with the AN/GRC-106 transceivers. I have a set installed in a 1965 M151A1 mutt and have lots of fun driving it around and setting it up and doing contacts that way. The 106 is a transceiver thatís designed around USB operation but in order to make it compatible with legacy equipment at the time of its deployment like the GRC-19 (R-392/T195) they included a AM mode. Like most SSB transceivers they do this by injecting a carrier along with the USB modulation. The most annoying thing about using it in the AM mode is that it always uses the product detector so if the other station is not exactly on the same frequency there are audio issues. Some of my newer radios like the Harris sets although still being primarily SSB transceivers do have an envelope detector so AM is a little more easy to copy along with having wider IF filters for the AM mode. It is interesting to see that on sets like my Harris URC-94 or RF-350K or the Sunair RT-9000 that I just got in they still have AM (AME) modes all be it just the USB carrier thing but at least itís still supported. Wonder if the Harris falcon (PRC-150) has an AME mode?
Although itís not true AM itís still at least somewhat AM. Think my favorite AM rig that I have is my ARC-38 plate modulated AM transceiver but rarely operate that. Also to support AM operations have my 1938 HRO RAS receiver and a WJ-8888 that are used for AM opps


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KB2WIG
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« Reply #1 on: March 19, 2018, 11:34:08 AM »



Well, you could get a Beastley 610... That's got a lot of watts in it.

I wonder what would happen if you fed "mono" programing into one of those ISB transmitters???

klc
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KA3EKH
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« Reply #2 on: March 20, 2018, 08:49:57 AM »

Was not unusual to have one ISB channel with two different voice or a voice and rtty circuit in operation at the same time, Think that was a big Navy thing.
 Never owned a BC-610, played around with them but not owned them. Think I would rather own that then a T-368 considering how weird the screen control and keying systems work on that. Also something has to be said in favor of the huge glass balls in the BC-610 and the basic goodness of simple triodes. The 100-TH modulators and the 250-TH PA are things of beauty, too bad they did not install windows in the transmitter like the old broadcast transmitters so you could watch them.

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KL7OF
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« Reply #3 on: March 20, 2018, 10:33:35 AM »

ISB was a Navy thing...They seemed to like it...The FRT39 Navy Transmitter is capable of ISB ....It takes about 8 days to get it set up and warmed up enough so it will operate ISB...the transmitter even has a built in  1 inch scope for "centering" your desired frequency.  It is my understanding that they could have several of these transmitters, somehow sync'ed together, each located in a different part of the world, transmitting the same programming on the same frequency ....To what end I don't really understand..The manual(s) weigh in at about 25 lbs.  so it takes some training to operate the FRT 39 in ISB mode.....
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KD6VXI
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« Reply #4 on: March 20, 2018, 11:16:16 AM »

Navy's version of a dead hand?

Any one xmitter goes out  all our missiles (read as miss aisles) would be launched.

Similar to the conspiracy theories surrounding squeaky wheel, etc.

Yes, tongue is in cheek.

--Shane
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KB2WIG
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« Reply #5 on: March 20, 2018, 11:33:11 AM »



I' m hankerin fer stereo am.



KLC
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KA3EKH
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« Reply #6 on: March 20, 2018, 01:35:41 PM »

C-Quam although think sky wave may be an issue. I installed a 5 kW Quam on WKEN back in the eighties. it sounded good at least in the city of license. way better then this whole Iboc thing.

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Patrick J. / KD5OEI
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« Reply #7 on: March 20, 2018, 07:44:55 PM »

I used GRC-106s. AMe mode.. very good audio quality too.
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Radio Candelstein - Flagship Station of the NRK Radio Network.
KA3EKH
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« Reply #8 on: March 21, 2018, 09:02:17 AM »

Always wondered about the quality of USB + Carrier as opposed to real plate modulated AM but then again if you listen to CHU out of Canada (7.850) that sounds completely normal and its USB + Carrier and not traditional AM
Think I must have some weird phobia about just using one side band from back in the days when they had audio processors that removed one side of the envelope and developed side bands that way, would think that introduces envelope distortion, but any SSB transmitter that uses a balanced mixer perhaps wonít introduce any distortion? Are audio waveforms after SSB processing clipped on one side or the other?

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KD6VXI
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« Reply #9 on: March 21, 2018, 09:58:35 AM »

In the 80s to dsp based rigs they used a balanced modulator, usually on a single ic.  That was then pumped through an xtal filter to slice off the opposite sideband.

On am, a lot of them don't use the xtal filter, instead using a 455khz ceramic only.  That equates to the WIDE position.

The dsp based rigs, am happens automagically!

--Shane
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SM6OID
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« Reply #10 on: March 27, 2018, 12:19:15 PM »

Hi!

Harris Falcon, PRC-138 and RF-5022R/T(E) are capable of AME.
Regarding ISB, I have had a few ISB qso using two microphones, left and right channel. Maybe not very meaningful...
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« Reply #11 on: March 27, 2018, 03:07:23 PM »


I kinda remember VOA running ISB for network feeds....    ?     


KLC
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WB2EMS
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« Reply #12 on: March 27, 2018, 11:11:07 PM »

When I worked for Harris Corporation we had some equipment in our installations that could run 4 ISB. Lower lower Side Band, Lower Side Band, upper side band, and upper upper side band. Each side band was a 3 kilohertz wide slice. We would often set up the system to run 2 voice channels on the upper side bands, and one or two teletype channels on the lower two or a third voice channel. The transmitter could run a pilot carrier at - 26 DB down for good phaselock. We built systems like this to carry voice and data traffic across North African countries in the 70s. I think the receiver in the system was an RF550. The transmitters came in one kilowatt and 10 kilowatt flavors. Pretty cool stuff to play with.


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73 de Kevin, WB2EMS
af6im
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AF6IM jumping from a C54G, 1999 Quincy Illinois.


« Reply #13 on: May 14, 2018, 05:38:09 PM »

EBay has CQUAM xmtr kits for sale right now. My 99 Chrysler 300 radio had a CQUAM decoder. As late as 2015 I found a couple of AM BCB stations still using it. They lit up a pilot light that said AM STEREO. Now HD AM seems to be the only AM stereo signals I can find on BCB. The HD AM sounds harsh, undersampled, kinda like DSTAR. CQUAM sounded great.

AF6IM
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