Hi Alan, Your link didn't work for me, but I assume your article describes how to make a good bandpass filter. I do in fact recall seeing such an article in QST years ago. Assuming that you were just pointing out that I can put a bandpass filter on each feedline, as is common practice in SO2R operations, I need to state my case in more detail:
Since I have second antenna covering 20-15-10 (a vertical), I started out doing just that: putting a bandpass filter on each. I was in a hurry and bought the LBS commercial filters rather than building based on the old article. The antennas are close together, and even after I upgraded so as to have two K3 radios, I was unhappy with the isolation with one K3 transmitting on 40 on the beam and the other K3 receiving on 20 on the vertical. Just out of curiosity I plan to dig deeper into this situation, as I think somewhat better results could be achieved. However, seeing the big difference in performance on a given band between the vertical and the beam, I really wanted both radios to have a beam. That is where I decided to get the multiplexer (a model that includes 40m). Performance wise, this was going to be like having one multiband beam, including 40m, for each radio. Much better than using the vertical for one radio, assuming of course that the physical sharing of one beam would aggravate the interference situation I had when using separate antennas and bandpass filters. With the multiplexer, per manufacturer's recommendation, each band still uses its separate bandpass filter, so that total attenuation between bands is much greater than what can be expected with bandpass filters alone. Still, I was apprehensive of a possible increase in interference. The outcome was nothing short of stunning: No interference at all. I see a possiblity that I could have somehow reduced the interference experienced with separate antennas and using bandpass filters, but I can't see that approach competing with the superior results using a single antenna + multiplexer + bandpass filters. The QST review backs up my assumption that the great results with that configuration was no fluke. Of course, I cannot include 80m in the same approach as long as I don't have a single antenna that includes that band (and I can't quickly get a multiplexer that includes all 5 bands). So, for 80 I will have a separate feedline and just a bandpass filter. BTW I am very happy to not have yielded to the temptation to upgrade my beam to a Steppir, as the multiplexer approach requires the antenna to be tuned simultaneously to multiple bands, not to tune to one band at a time. If I had been able to achieve really good isolation with just a bandpass filter for each band, your approach with an 80m antenna that also covers 40 would make good sense to my situation. As it is, keeping 40m within the beam, even with no gain over running 40m on the second antenna, makes sense as it allows me to route 40m not just through the bandpass filter, but also through the multiplexer. Since I already tried an 80m inverted vee on the tower, and it ruined the 40m performance of the beam, I am looking for other approaches for 80m. It might be possible to change the beam to bring it back to resonance on 40, but this particular beam is a complicated design already. A sloper is one possiblity, but it is not likely to be my first attempt, as it would be close to the beam and it would be somewhat similar to the vee. At this point I am leaning toward either a separate shortened vertical such as a Butternut model for 80 and 40 (not likely to use the 40 part) or using the tower itself as a vertical. For the latter approach I would need to prevent the tower's feedline bundle (the part going into the house) from forming part of the radiating element. I remember an old Antenna Book discussing methods of feeding the tower as a vertical, but the author seemed to ignore the issue of the cables coming off the tower. Maybe it was assumed that the cables would be disconnected at the bulkhead whenever the tower would be used as a vertical. Nobody has replied to me about experiences dealing with that issue. Also as the tower with its antennas is resonant in the BC band, I would model it to find out if it has a resonable vertical radiation pattern if fed as a whole on 80. 73, Erik K7TV -----Original Message----- From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Alan Bloom Sent: Wednesday, March 01, 2017 12:29 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] Using your tower as a vertical - 160 or 80 Hi Erik, It is certainly possible to use a separate filter in the feedline to each antenna. For example, here's an article I wrote many years ago on how to homebrew your own: http://p1k.arrl.org/pubs_archive/89595 Those filters are only good for 100W or so, but there is no fundamental reason they couldn't be scaled up to 1500W. I haven't researched it, but I'm thinking there must be commercial equivalents as well. Alan N1AL On 02/28/2017 10:41 PM, Erik Basilier wrote: > Alan, > > Thanks for your reply. Your approach would provide 40m capability to > replace the 40m capability that my (Sommer) beam loses through detuning. > However, I wonder how hard your tuner must work on 40? Enough to > create substantial feedline losses when the tuner is in the shack? > Anyway, I have another reason not to choose your approach: > I am rebuilding my station to support SO2R, and it is tough to avoid > interference between the two radios operating on different bands, > especially > 40 - 20 and with the antennas close together. > I found to my surprise, before the QST review came out, that the Low > Band Systems multiplexer and band pass filters (my setup includes 40m) > eliminates the interference problem. However, this scheme requires > that the antennas be on a shared feedline. With your approach the 40m > antenna would no longer be on the same feedline as the higher bands. > > > > -----Original Message----- > From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of > Alan Bloom > Sent: Tuesday, February 28, 2017 11:09 PM > To: elecraft@mailman.qth.net > Subject: Re: [Elecraft] Using your tower as a vertical - 160 or 80 > > I use two of the top guy wires as an inverted vee. There are > insulators near the top of the guys and about 50 feet or so down. The > vee is brought to resonance on 80 meters with a center-tapped loading > coil, which also acts as a balun. The best match was with the coax > tapped right about at the end of one side of the coil (and of course > the coax shield to the grounded center tap). > > Works great on 80 meters without a tuner and on 40 meters with a tuner. > > Alan N1AL > > > On 02/28/2017 09:42 PM, Erik Basilier wrote: >> Years ago, after putting up a heavy-duty crank-up tower with several >> antennas on a tall mast at the top, I was interested in loading up >> the whole metal tree for 160 and/or 80. However, I didn't like the >> prospect of transmitted power getting back into the shack via the >> existing feedlines, causing all kinds of problems including losses. >> From a surplus vendor I obtained four square slabs of ferrite (no >> spec's) and taped them together to form a box-shaped common mode >> choke around the existing feedlines (and rotor control cable etc). I >> didn't have radials at the tower base, but a couple of long and wide >> copper strips buried and connected to ground rods to which the tower >> was grounded. I opened up the tower ground connection and I had a >> feed point. Finding resonance was not as easy as using my antenna analyzer. >> The signal from the analyzer was overwhelmed by picked-up broadcast > signals, rendering the analyzer unuseable. I got by using a custom > measurement setup. >> It turned out that the entire metal tree resonated in the broadcast >> band and was inductive at 160. I tuned it with a serial variable >> capacitor, and found the antenna worked very well on 160. However, I >> didn't continue using it, as I didn't feel safe not to have the tower >> grounded. I pondered schemes to add some kind of gamma-like matching >> device, but never got around to it. Also I never tried it on 80, but >> I suspect it would not been ideal for low angle radiation. >> >> >> >> Later I added more antennas to the mast, and with the added cables, >> the whole bundle would no longer fit in the makeshift ferrite choke. >> Out of curiosity I once again tried ungrounding the tower to check on >> its characteristics as a vertical antenna. I could no longer find the >> resonance I had seen and used before. Apparently, the ferrite choke >> had been a crucial part of the scheme. >> >> >> >> At this point I still don't have an antenna for 160 or 80. (I did try >> an inverted vee off the tower for 80, but it caused terrible >> de-tuning of the 40m part of my beam on the tower, so I gave up on >> that. Maybe I should try a >> sloper.) I am thinking of putting up a dedicated vertical, but on my >> small lot it would couple to the tower. Perhaps it would be better to >> give the tower another look as my low-band vertical? My source of >> ferrite slabs dried up years ago. I wonder if anyone else on the list >> has used a similar approach and found a good way to choke off RF on a > bundle of feedlines? >> Individual chokes don't seem very attractive to me as I have many >> cables, but if one has to go that route then it would make sense to >> look very carefully at the choice of chokes. I would also be >> interested in knowing about others' experiences with feed systems >> that > leave the tower grounded. >> >> >> >> Thanks in advance for any useful ideas! >> >> >> >> 73, >> >> Erik K7TV >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net Please help support this >> email >> list: http://www.qsl.net/donate.html Message delivered to >> n...@sonic.net >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net Please help support this email > list: http://www.qsl.net/donate.html Message delivered to > ebasil...@cox.net > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net Please help support this email > list: http://www.qsl.net/donate.html Message delivered to > n...@sonic.net > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to ebasil...@cox.net ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
