On 8/8/2015 6:23 AM, Bill Frantz wrote:
The other interesting diversity mode I know of is the way the costal commercial communication radio stations worked in the 1930's and later. They were using CW to send messages across the oceans. Each station transmitted on 3 separate bands. The receivers listened to all 3 bands and routed the "best" signal to the operator. (I don't know how they determined the best signal using 1930s technology.) Obviously a two channel version could be assembled using a K3 with a sub-receiver.
Well, at least in 56-57, it wasn't exactly diversity [I worked at a coastal marine station for 11 months during that period when I was a HS senior]. Coast stations [three letter calls] were assigned specific ITU-defined channels [freqs] in each of the maritime bands, both MF and HF. Everyone could use 500 Kcs.
A coast station would transmit its "wheel" on all of its assigned HF frequencies, except those for which there was no propagation, such as 22 Mcs at night. The wheel might have comprised:
VVV VVV VVV DE KOK KOK KOK QTC <list of ships for which KOK was holding traffic> QSX <list of MF/HF maritime bands on which KOK was standing watch for calls> AR.
The QSX was followed by the band designators only, such as "4 6 8 12", the ship operator had a printed directory of the assigned frequencies in each band. HF channels were full-duplex, coast station on its assigned frequency, ship on the second frequency in that band paired with the coast station.
When the operator afloat opened his watch, he would start the log and listen for his company's station wheel. If his call was in the list, he called the station, the traffic was passed, his call was removed from the wheel [usually paper tape] and the wheel continued. In most [but not all] cases, the operators on the ships worked for the same companies that owned the various coast stations.
So, while multiple frequencies were involved in this process, the ship was almost always on only one, so it wasn't really diversity reception in the technical sense. 500 Kc [600 meters, the "Holy Frequency"] was a huge, simplex, world-wide party-line.
A system where you can automatically determine which receiver has the better signal, could be useful for RTTY. Measuring the difference in signal strength of the mark and space signals compared with the signal strength half way between them might be a useful technique.
In the mid-60's [while in the US military in SE Asia], we used real diversity on multi-channel troposcatter systems. The AN/MRC-98 was an example. In the 450-550 MHz range, 2-10 KW transmitters to two 9.1 meter dishes, each with two cross-polarized feed horns. 4 receivers, 2 each on each of the two frequencies with phase locked local oscillators for pair. 60 good quality telephone channels over 400-500 km paths. Modulation was FM, the combiner watched the SNR from each RX [which varied all over the place], and added the basebands together using all analog circuitry for best output SNR. The two PA's were Eimac klystrons, about 1.6 meters long. Space, polarization, and frequency diversity.
It was somewhat mesmerizing to sit in in front of the receiver bank and watch the SNR on the single receivers fluctuating wildly while the SNR on the baseband would drift very slowly up and down in very small increments.
73, Fred K6DGW - Northern California Contest Club - CU in the 50th Running of the Cal QSO Party 3-4 Oct 2015 - www.cqp.org ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
