well....IMHO, i think the cited factors may slightly overstate the case.. ....of course 'it depends' on 1: what kind of antenna you use...an end fed half wave longwire brought directly into the shack is GOING to put you in " the presence of strong RF fields that usually accompany amateur radio transmissions" especially at legal limit power levels. likewise any antenna that is 'close' to the shack, in terms of wavelengths; e.g. a dipole 20 ft above you. otherwise, a good common-mode choke at the rig and feedpoint can offer considerable mitigation...
2: how long that cable is, between the pc and the radio, especially in term of wavelengths...whether its firewire, usb, or ethernet..and whether it is adequately choked for optimum common mode rejection with the correct mix of ferrite... 3: the quality of RF grounding for both the pc and the rig, and the integrity of their shielding. plus, the amount of common mode rejection of r.f. on the ac power lines and anything else that connects to either. 4: and, of course, how much power you're running... my 2 cents worth...w5xz, dan 4: 3: t --- On Thu, 5/5/11, [email protected] <[email protected]> wrote: From: [email protected] <[email protected]> Subject: Re: Re: [Flexradio] [FlexEdge] Firewire vs. USB vs. Ethernet To: [email protected] Cc: [email protected], [email protected], [email protected], [email protected] Date: Thursday, May 5, 2011, 9:04 PM Best evaluation of the three interfaces I've seen yet. Clear, concise, and to-the-point! 73, Jim KQ6EA May 5, 2011 01:49:29 PM, [email protected] wrote: well, that sure makes ethernet look 'good'.....plus, ethernet wires are 'twisted pairs' which 'mr.- RFI - solutions - himself' Jim, K9YC, sure likes....for common mode rejection.. 73, w5xz, dan --- On Thu, 5/5/11, Brian Lloyd wrote: From: Brian Lloyd Subject: [FlexEdge] Firewire vs. USB vs. Ethernet To: "FlexRadio reflector" , [email protected], [email protected] Date: Thursday, May 5, 2011, 8:30 PM It is really interesting to see that arguments going on, mostly over Firewire vs. USB and how USB would be a better choice, probably as a result of the greater prevalence of USB. After all, with USB 2.0 having speeds comparable to IEEE 1394a (400Mbps Firewire) and USB 3.0 being much faster, doesn't using USB make a lot more sense? And then there is the question of Ethernet. People have been talking about the efficacy of Ethernet relative to IEEE 1394 and USB as well. This is actually an amazingly complex question all around but there are some aspects that are quite specific to amateur radio and are relatively easy to understand, mostly having to do with the nature of RF. In all three cases; i.e. USB, IEEE 1394a, and twisted-pair Ethernet transmission; we are sending serial digital data at relatively high rates of speed over wire between devices. Since all three accomplish this task in a different manner, HOW this is done has a direct impact on the success, especially in the presence of strong RF fields that usually accompany amateur radio transmissions. When you place two devices in an RF field connected by a conductor, you *will* induce RF currents in the conductors. That is a given. It is how antennas work. In this case what we want to do is to reduce the RF currents to a minimum so as to have the least impact on the data communications between the devices. There are several things we can do to reduce the effect of the RF field on the data being transported by the wires. They are: 1. Reduce the RF currents on the wire. 2. Structure the transmission of data so that induced RF currents are not mistaken for data (interference) at the receiver (the data receiver in this case, not the amateur device intended to receive signals out of the air). The most common way to deal with these things is to transfer data over a differential (balanced) transmission line. Since the desired signal current in each wire of the pair is equal and opposite (differential) and the the undesired induced signal is the same in both wires, it is possible to reject the unwanted common-mode signal. Further, you want to come up with some way to break the path for the common mode currents. You want to raise the impedance to common-mode currents substantially at the RF frequencies involved on both the data and the the ground or shield between the devices. One of the simplest ways to do that is to break the physical connection and make sure that there is very little coupling at RF. One of the best ways to accomplish this is with a properly-designed transformer. So if we look at the three technologies and compare how they fare in this situation, you come up with the following matrix: Ground Differential Transformer Isolation decoupling USB no no no IEEE 1394 no yes no Ethernet yes yes yes So, as you can see, from just an RF-point-of-view USB is the *least* desirable of the three interconnects. So don't be rushing off to support USB without a full understanding of the issues involved. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 [email protected] +1.767.617.1365 (Dominica) +1.931.492.6776 (USA) (+1.931.4.WB6RQN) _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software. _______________________________________________ FlexRadio Systems Mailing List [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software.
