[Elecraft] Center-fed antennas

[Don Wilhelm]

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 <donwilh at embarqmail.com> 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
>>>