Thanks all for the great advice and the further reading. In my specific case of K3S + KPA500 + KAT500, is there no room to reduce the high performance W3NQM filters?
I understand common mode filters and have made good versions of these from K9YC cookbook. They remain in circuit all the time, so that's easy, whilst NQN filters have to be replaced for each band change, so, even I want to have a quick peek at another band, it still takes minutes to swap around the filters with the other station. It's a painful loss of time and prone to getting it wrong. Building a lower specification filter set with relay switching would be easier. David G3UNA > On 27 July 2021 at 20:53 Morgan Bailey <mbaileyc...@gmail.com> wrote: > > > 80 to 100 dB band to band attenuation is necessary for a contest station. > Reviewing Contest University the RA6LBS talk from a few years ago is the > basis for this decision. He probably has the most experience in this field > beside that of VA6AM. Both make great filters. Just having a filter is not > enough. One needs a multiplexer in conjunction with the band pass filter to > get to that DB level. One could stack 2 band pass filters and attain > whatever is needed to get the job done. The multi switchable boxes that run > about 500 to 900 dollars only give about 30 to maybe 40 db of rejection. It > is just not enough to keep the other radio quiet and SAFE from front in > overload and toasting the receiver circuits. I use transmitting band pass > filters rated at 3500 watts on the output of my amp. This coupled with > multiplexers on 160/80/40 and 20/15/10 makes for a multi two or an SO2R > setup quiet on each radio. Between the multiplexer and associated band pass > filters I am able to run 1.5KW 160-10 with an antenna farm that takes up 68 > linear feet total for 160-10. Additionally, 160/80/40 are vertical > polarized and 20/15/10 are horizontal polarized adding more rejection. It > works and works well. > > One problem that many stations on a small lot have is ignoring Common Mode > pick up off the shield of the coax. Grounding all shields before entering > the shack and using 1:1 choke baluns is a necessary step to prevent > interstation interference. > > Having radios with very low composite/Phase noise is necessary. I use > FTDX101 radios in the shack. If radios are noisy and they raise the noise > floor of the other radio during reception, about the only solution is to > get a new radio that is clean on the output. Check out the Sherwood > engineering pages for those ratings. While you are there, one may want to > check out the ratings of ADC front ends vs Superhet front ends.Hybrid > superhet/ADC front end receivers seem to be the best choice for this > environment at the moment. RMDR and Close in blocking dynamic range are the > magic numbers to review. > > 73, Morgan Bailey NJ8M > > BS + MS + $2.98 = COFFEE > Real Life Experience = Priceless, says the man who set his back yard on > fire with a breadboard tuner loading a 160 meter inverted L with 1000 > watts. LOL > > > On Tue, Jul 27, 2021 at 1:52 PM David Hachadorian <k6ll.d...@gmail.com> > wrote: > > > You need a filter on the TX radio to prevent its phase noise from being > > heard on other bands. Just pressing PTT on the TX radio, even without > > putting out any measurable power, will raise the noise floor on multiple > > bands. With suitable band decoders driving filter selection, > > fast-switching between bands is possible. > > > > Dave Hachadorian, K6LL > > Yuma, AZ > > > > > > On 7/27/2021 9:09 AM, CUTTER DAVID via Elecraft wrote: > > > Given the improved performance of modern transceivers, is there still a > > call for high specification W3NQN band pass filters in a 2-transmitter > > station? For example on a Multi-2 contest environment. For instance K3S + > > KPA + KAT. The filter fitted between radio and amplifier. > > > > > > I have the *feeling* that a receive-only filter (with tx bypass) might > > be all that is needed. This is much easier to implement than a full > > transmitter-rated set making fast switching between bands (eg for a quick > > look around) very quick and easy from the keyboard, etc. > > > > > > David G3UNA ______________________________________________________________ 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
