http://elecraft.85.s1.nabble.com/KX2-Antenna-Curiosity-tp7655612p7655639.html
As usual, there are exceptions to everything. A multi-band beam, such as a C3S or the modern equivalent, will perform incredibly well when used with bandpass filters and a triplexer. The 10,15 and 20 meter stations all will use the antenna through the triplexer/BPFs with no issues. This also turns out to be a favorite setup for many SO2R and M/2 stations at both low and high power. The key is port-to-port isolation through the triplexer/BPFs. It is extremely important that all components can handle the power level in use. Also very important is that the radios have very low spurs and phase noise (i.e. need to have clean signals on transmit). The K3/K3S meets the bill, as do recent Flex Radio SDRs. As Rob Sherwood has pointed out recently, the transmit issue (See Oct QST and hi Dayton Contest Forum talk this past May) is pretty big in most radios. They have been paying attention to receiver issues, but not transmitter. We are very lucky that Wayne, Eric and friends have been p
> On Oct 10, 2019, at 4:44 PM, Don Wilhelm <
[hidden email]> wrote:
>
> Bob,
>
> Bandpass filters at each station will help a lot, but they do not have infinite out of band rejection.
> There is still a huge benefit with single band antennas. My club uses both.
>
> Last Field Day (3F operation) one station got on the air with a multiband vertical, and all other operators jumped on that operator to shut him down quickly! The multi-band antenna radiated harmonics of the radio. Even though the transmitter met the -43 dB harmonic required by the FCC, the proximity of the multiband antenna to other antennas caused problems (that station was not using a bandpass filter).
>
> So for Field Day multi-station operation, single band antennas, bandpass filters and transmitters with low phase noise are important. We were not able to orient the antennas end to end due to space considerations at the EOC site, so we had to compromise on that, which makes the other factors very important.
>
> I need to point out that as an experiment, a 2nd station used an antenna on 20 meters separated from the main 20 meters, and we were able to operate one on CW (K3) at the same time as the other station (Icom) used digital and SSB modes. We had some mutual interference, but it was minimal. The K3 did not interfere much with the Icom due to the K3's low phase noise, but the Icom did raise the background noise level on the K3.
>
> 73,
> Don W3FPR
>
> On 10/10/2019 7:12 PM, Bob McGraw K4TAX wrote:
>> I thought a Band Pass Filter at each station resolved that issue.
>> 73
>> Bob, K4TAX
>> On 10/10/2019 5:27 PM, Ken G Kopp wrote:
>>> Well-said, Don.
>>>
>>> 73!
>>>
>>> Ken Kopp - K0PP
>>>
>>> On Thu, Oct 10, 2019, 16:23 Don Wilhelm <
[hidden email]> wrote:
>>>
>>>> All this talk of multi-band antennas for Field Day ignores the problem
>>>> of multi-station Field Day operation.
>>>> There is sufficient pickup of one transmitter's energy on the antenna
>>>> being used by a receiver on another band.
>>>> For that reason, my club has banned the use of multiband antennas for
>>>> Field Day operation.
>>>>
>>>> For a single station Field Day operation, the multiband antennas are great.
>>>>
>>>> 73,
>>>> Don W3FPR
>>>>
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