Bandpass Filters

[k3lr]

I have been working with and using single band transceiver 
filters designed and constructed by filter expert W3NQN. 
These are high performance bandpass filters for multi 
transmitter operation. 
 
I started out using W3LPL receiver front end filters 
in the early 80's. I then purchased the receiver filters 
that were used at W2PV. Both the W3LPL and W2PV
filters do a fine job at eliminating receiver front end 
overload from nearby transmitters on different bands.
 
When we started operating multi-multi in the early 90's,
I wanted to reduce the interfearence that was generated by
the transmitters. I ordered two complete sets of ICE transceiver
bandpass filters. These filters helped, but I was
having failures and I wasn't happy with the network anaylisis. 
Their bandpass loss specifications were not optimum (.5 to .8 dB)
, worse than expected return loss (-10 to -18 dB). The adjacent 
band loss was poor is some cases (80 meter filter on 40 is only 
-16 dB). I beefed up the capacitors in the ICE to reduce the 
transmitting failures (70 watts on 10 meters driving a tuned
input amplifier), but I thought there might be a better solution.
 
Last year around this time I started talking to W3NQN about the
ICE bandpass filter problems. Ed has now designed and constructed
200 watt continuous duty, hi performance, single band,
transceiver filters. I have tested their performance with an
HP Network Analyzer and found them to be top performers!
 
Bandpass loss is .3 to .5 dB. Every watt counts when you are 
driving an SB-220 with a 100 watt exciter. Adjacent band
rejection is 36 to 40 dB. I have put 200 watts into each filter
for 45 minutes without failure or excessive heating of
the components.  
 
We first used the 80 meter filter during the 1996 ARRL DX 
contests at K3LR.
At WRTC, the VE3EJ/VE3IY, K8CC/K5GO and K3LR/N9RV teams all used
40 and 20 meter NQN filters with good success. (15 and 10 meter 
filters were still being designed). This past fall
the K3LR, N2RM, KS9K, VE3EJ (HC8 team) and K8CC multi op
teams used the first run of W3NQN filters. Prior to this, 
all of these stations were using ICE single band filters. 
 
If a filter component fails during a contest or the design is poor
it will cost you QSOs. I think the W3NQN bandpass filter has 
solved my transmitter and receiver filtering problem.
 
As a favor to W3NQN (for taking the time to design these 
filters), I have tested and aligned each filter that
he has constructed. I have them in hand, although I have no
financial interest in them. There are a limited 
number of filters available. Contact me if you are interested. 
 
There are no plans to build a multiband (relay switched) 
filter arrangement, sorry.
 
I am now testing high performance AC line and AM
broadcast rejection filters. I'll keep you posted
on the results.
 
73!
Tim K3LR
 
K3LR@contesting.com
 

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