Hi Tom (and others), I think Don answered almost complete to your question but I'd like to elaborate a little on this subject which is unnecessary for and even unknown by most HF operators.
For serious VHF/UHF operation, it is important to have a system with low noise figure (typical between NF=0.1 to 0.5 dB). For HF typical NF can be between 3 to 10 dB. The ONLY way to reach this factor is by putting a preamp as close as possible to the antenna. Each dB of cable loss, will raise the NF with the same level and makes especially moonbounce more difficult or impossible. A preamp in the top of the tower means at least 1 coaxial (power) relay at the same position. These ralays have to be coaxial, and are not that fast due to the mechanical construction (bigger distance between contacts to enable big cross attenuation). Switching times are typical longer then 20 msec. To make absolutely sure that the relay has switched over, I (and many more VHF operators) gets a feedback from the relay itself. Don't forget that all is outside and vulnerable (cables, connectors etc). Another issue in sequencing is that many VHF amplifiers are not build with zero-bias tubes. So the grid voltage has to be raised and stable before injecting RF at the input. To overcome this problem and additionally prevent hot switching, a sequencer is needed and 20 msec is not enough. A complete RX>TX sequence may even need 500 msec. Here my motivation for an addition/change/option in the K3: It would be far too much to ask Elecraft to develop and/or integrate a sequencer. But as the Mic-PTT, external PTT, VOX, Key and/or paddle is already combined into 1 single TX request (to the central processor) in the HF-rig which finally puts the TX voltage on the parts needed (8T line) it would be much more efficient for a small group of Elecraft users if that signal is made available at one of the acc connectors. A TX-enable signal from the sequencer to the HF-rig could close the loop or complete the sequence so to say. In my opinion it is almost all about software and could be activated only in the tranverter mode of the K3. A regular HF user won't even notice this option and therefore there is no need for a special VHF version of the K3. So why not if it makes the radio interesting for this group. And don't worry, we will design, build or buy our own sequencers. There are several thousands of serious VHF/UHF-ers. We are a market opportunity, not a thread :-). We are not buying Elecraft equipment because its appearance, but because it works so great and meets our expectations! 73's, Evert PA2KW For 144 Mc Ant: 2x16 el Preamp: NF 0.3 dB PA: YL1056 2.9 kW XVRT: Home designed and build TRCV: K2(4836) For HF: Ant: Optibeam OB11-5 / Alpha-Delta DX-B PA: Drake L7 TRCV: Drake TR7/R7 _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
