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Text File | 1992-06-28 | 8.0 KB | 131 lines

NET_14.TXT HF NETWORKING AND PRACTICES --------------------------- Casual observations of HF networking reveals it's even more vulnerable to poor operating practices than are the VHF systems. Somewhere along the line it appears packet has been vastly oversold as to what can and what cannot be accomplished. Due to the longer amount of time it takes to pass a given amount of data at 300 baud, as compared to 1200 baud, transgressions become painfully obvious. We have often succesfully passed packets on HF for an hour or more at signal levels approaching the noise with scarcely a retry. In every case this occured when there was only ONE SET of stations on frequency. The instant another packet station came on, the retry rate went up and throughput dropped. If the new station's signals were very much stronger, we typically would retry out and become disconnected. From this it's concluded marginal signals on a MULTI-USER ACCESSED HF CHANNEL have little chance of successfully passing much data. Even though packet is a multiple user access mode, there are very definate limitations as to the number of users a channel can accomadate. Many packet operators believe it's okay to zero in on an active HF packet channel. They connect to other stations and go about their business quite oblivious to the damage created to the original on-channel stations. While communications can be achieved on a lightly loaded HF channel, in general, throughput between one or more sets of stations will suffer. This is true even if all stations have good signal strengths. When conducting direct on-channel QSO's on a node\gateway frequency it's proper operating practice once contact is made to move off the channel. This practice expedites not only YOUR communications, but those through the gateway as well. By the same token, operating MULTIPLE STREAMS on an active channel can cause serious disruptions to other conversations. Maximum throughput occurs between two HF forwarding BBSes when THEY ALONE occupy the channel and have signal strengths somewhat above the noise level. In this regard, packet is little different from having multiple voice, CW, or RTTY stations attempting to pass on-channel traffic at the same time. In many instances, channel discipline has broken down. Multiple stations attempt to forward at the same time. Some BBS forwarding stations use incredibly long TXDs on the order of two to three seconds. This helps them to "capture" the channel, but at the cost of vastly reduced throughput for everyone concerned. A TXD of 100 milliseconds is typical for quiet channel operation with modern radios. Where possible, network managers should assign forwarding stations time blocks tailored to the best propagation periods between partners. The practice of allowing BBS/nodes to send beacons and NODES broadcasts on forwarding channels should be discouraged as it hinders throughput. Besides using a QRM-free frequency, successful forwarding operations requires thought be given to propagation paths and station equipment. Forwarding partners should be geographically established to take advantage of optimum skip conditions for the band(s) involved. A helpful aid is the MINIPROP program. Inputting HF station locations and current sunspot data into MINIPROP will easily reveal optimum distances and frequency bands for this purpose. HF transceivers should have sufficient frequency stability. Excessive retries WILL occur if both partners aren't netted to each other within 30 Hz. Crystal control will solve many stability problems. A 500 Hz IF filter is mandatory for optimum performance. TNCs will give superior results if equipped with the HF DCD modification. Nearly any TNC will work equally well on HF if it has the DCD mods and is preceeded by a 500 Hz IF filter. It's desirable to use a gain antenna, preferably a beam, for the higher frequencies. Antenna height should be matched to the forwarding partner's optimum take-off angle (MINIPROP displays take-off angles). Even modern high priced digital radios may have inaccurate dial calibration. A simple way to check calibration accuracy uses a frequency counter connected to receiver audio. In one of the SSB modes, tune to a dial setting 1 KHz off an UNMODULATED carrier known to be accurate (WWV, service monitor, etc.). The counter will read 1.0000 KHz if the radio's reference oscillator is correct. While the lower HF bands have borne the brunt of forwarding, the ten meter band has been under utilized. 1200 baud operation is authorized above 28 MHz. Yet very little forwarding activity has taken place. Around 28.105 MHz, 300 baud operation is popular. At 28.190 MHz, 1200 baud forwarding occurs. Just as on lower frequencies, the "herd instinct" prevails, thus overloading the channel at times. A BBS-free node/gateway ragchew 1200 baud channel exists at 28.195. From time to time, BBS SysOps, TCP/IPers, or DXCluster Ops insist on uninvitedly setting up camp on the channel. While everyone has a "legal right" to operate on any frequency within the amateur bands, the standards of courtesy are no different with packet then they are for any other mode. Even on the "dog-eat-dog" 20 meter band, one often hears a voice politely asking: "Is this frequency in use?" Packet operators, especially those with servers capable of causing considerable QRM, should enquire whether their activity is wanted prior to establishing operation on ANY frequency. Compared to the lower frequencies, 10 meters has a vast amount of room for packet operation. With proper antennas, and attention paid to propagation paths, inexpensive low power converted CB radios at 1200 baud will move an impressive amount of data. Considerable presssure on the lower bands could have been eased had more effort been made to coordinate individual forwarding partners on 10 meters. This band would make an ideal 1200 baud wide area network (WAN) for TCP/IP experimentation. A drawback with 10 meters is that the band is open only during a few years corresponding to the peak of the 7 year sunspot cycle, and then, mostly during daylight hours. However, during this period great propagation exists that could be used to good advantage. A significant chunk of the digital band is taken up with unattended CW beacons. When the band is open, these tend to cause harmfull interference to the other authorized modes. An interesting propagation experiment would be to replace the existing CW beacons with packet nodes. Initially the nodes could operate on one frequency and be widely spaced over the globe. TheNet's dynamic routing will automatically list other nodes when propagation allows their broadcasts to be heard. Node routes listings would be available for inspection by local packet stations at any time. An advantage of using packet nodes vice CW beacons here is that propagation info will remain in the routes list for several hours after the condition goes away. Those interested in recording propagation conditions need only to check the routes list on their local node from time to time. Otherwise, with CW beacons, one has to monitor or tape the channel constantly. In addition to propagation info, this concept would allow networking channels when conditions allowed. If and when automatic unattended packet operation is allowed, these nodes could be gatewayed into existing VHF/UHF packet networks. To summarize, should this proposal be adopted, 200 KHz or so of CW beacons would be phased out in favor of packet nodes on perhaps, only 1 - 5 descrete channels. Such implimentation would conserve frequency resources, and possibly prove (or disprove) the theorem that 10 meters is open to someplace in the world at all times.