[TowerTalk] Field Day

[Jim Brown]

On 6/29/2017 9:19 AM, Herb Krumich via TowerTalk wrote:
> Every year after field day questions are raised for the following yearHere is mineWhat do big clubs do about operating CW and SSB on the same band ?I see no filters that are that tight.My only thought is to have the antennas as far apart as possible.Possibly one being vertical and the other horizontal.Your thoughts please

Good question, and the answers are nothing more than the fundamentals.

1) Use ONLY radios that are clean on transmit and whose receivers have 
good strong signal overload and rejection. The link is a summary of the 
transmitter cleanliness measurements by ARRL Labs of a selection of rigs.

http://k9yc.com/TXNoise.pdf

El cheapo  entry level rigs like the IC706, FT897, and others that work 
160M to 440 MHz FM have no place in multi-transmitter environments. And, 
as the link shows, the most expensive rigs are not the cleanest ones. 
Some of the best choices for FD are the Elecraft K3, K3S, and KX3, and 
the Flex 6500/6700, which are fairly expensive, and the Kenwood TS590S 
and SG, which are not. In general, Icom and Yaseu rigs are dirtier than 
the other brands, generating more trash away from their TX frequency.

Likewise, for receiver overload, Rob Sherwood's website is a great 
resource. The rigs listed above all show up well in his tests.

2) Antenna separation is also critical.  An ideal setup would have 
antennas for the same band widely separated and co-linear (that is, on 
the same line, several hundred feet apart).

3) All antennas should be resonant, fed with coax, and have a serious 
ferrite common mode choke at the feedpoint (that is, up in the air).

4) Off-center fed antennas are a recipe for disaster in a 
multi-transmitter environment, because their feedline radiates.

5) Bandpass filters can minimize interference between stations on 
DIFFERENT bands, but do NOTHING for rigs on the SAME band.  Some 
bandpass filters are a lot better than others, and the poorest ones are 
VERY intolerant of mismatched antennas (that is, they fry).

http://k9yc.com/BandpassFilterSurvey.pdf

6) I've always viewed FD as a low power and QRP event -- high power is 
like a #&%$ in the punchbowl. If you MUST run high power, use clean 
power amps, stubs after the power amp, carefully located on the coax 
line. See the link below.

http://k9yc.com/LocatingStubs.pdf

Our county expedition group for the California QSO Party has very 
successfully run CW and SSB on the same bands (80-10) with 500W stations 
and colinear dipoles separated by about 250 ft on 80 and 40 and 
tribanders separated by about 200 ft on 20-10.  Each station is a K3S 
and KPA500, with a KAT500 tuner for 80 and 40.

The better your radios, and/or the lower the power level, the less 
separation you need. 100W to 500W is 7 dB, and the difference in 
required separation is about 2:1.

Here's a setup our county expedition group uses for 7QP, where we run 
two 500W stations that are never on the same band. k9yc.com/7QP.pdf  
Again, K3S, KPA500, KAT500, bandpass filters, and double stubs on the 
80M and 40M antennas.

And we are serious about RX noise. If you can't hear 'em, you can't work 
'em. :)

http://nccc.cc/pdf/CQP-RFI2013-2.pdf

Another point about the cost of rigs. Some older models, bought used, 
are great choices. An original K3 can be found for about $2K, a used 
TS590G for about half that.

73, Jim K9YC