[TowerTalk] Bandpass Filters

[Peter Forbes]

Absolutely Al,

The filters work in two ways:

On receive you have minimal receive insertion loss at the frequency it is 
designed for and deep notches (up to 80dB) on the adjacent bands.

On transmit you have minimal transmission loss on the frequency it is 
designed for and heavy reduction up to 40dB per octave on adjacent 
frequencies and in the case of the 3 resonator W3NQN design, this reduction 
is equally good both above and below the design frequency, whereas with the 
earlier 2 resonator designs it is not.

I have found that the filters work particularly well on attenuating the 
wideband phase noise that solid state transceivers with their switched range 
low pass filtering systems use.

For example, on the FT100D (and similar Yaesu transceivers), the low pass 
filters switch in at 2.5,   4.7,   7.5,   14.5,   21.5,   33.0 and 70.5 Mhz, 
so if you are transmitting on 10.1 Mhz, your wideband noise all the way up 
to 14.5 mhz is being transmitted equally well at the same time.  Similarly, 
if you transmit on 18.1 Mhz, your noise on 21, 24 and 28 is being 
transmitted.     This often explains why certain expeditions have 
difficulties with particular combinations of transmitting on multiple bands 
simutaneously and not other combinations.

The use of the W3NQN filters on each transceiver, eliminates this problem 
pronto!   (Even if you have amplifiers added after the filters, by the way.)

So essentially, for best performance, you need them both on transmit and 
receive.

Cheers

Peter   VK3QI


----- Original Message ----- 
From: "Al Williams" <alwilliams at olywa.net>
To: <towertalk at contesting.com>
Sent: Thursday, January 10, 2008 1:02 PM
Subject: Re: [TowerTalk] Bandpass Filters


If one has a bandpass filter such as Dunestar or ICE and switch it in for rx
and out for tx, is that good enough or is there really a filtering advantage
of transmitting through the filter when nearby ax's have their filter in
place?

k7puc


----- Original Message ----- 
From: " Peter Forbes" <prforbes at bigpond.net.au>
To: "Alfredo Vélez WP3C" <wp3c at usa.com>
Cc: <towertalk at contesting.com>
Sent: Wednesday, January 09, 2008 5:20 PM
Subject: Re: [TowerTalk] Bandpass Filters


Alfredo,

How much power do you intend running through the bandpass filters?

If you are using the newer rigs which can run 200 watts out, then you might
have trouble with the Dunestar and ICE filters drifting with temperature
increase.

The W3NQN filters are rated for 200 watts and do the job well.  I have built
copies of the W3NQN filters for our IOTA operations over the last 4 years
from VI5BR, VI5PN, VI5WCP and VI3JPI and they work very well.

Even though the W3NQN filters are more expensive, you do get what you pay
for, with better power dissipation and in some cases, better notches on
certain band combinations.

Cheers

Peter   VK3QI


----- Original Message ----- 
From: "Alfredo Vélez WP3C" <wp3c at usa.com>
To: <towertalk at contesting.com>
Sent: Thursday, January 10, 2008 10:10 AM
Subject: [TowerTalk] Bandpass Filters


Hi

I would like to know your opinion about Bandpass filters, soon I will be
updating all my station and I will make it to operate a SO2R and M/S, so
i see that there are W3NQN Dunestar 600 and the ICE (if there are others
please let me know) I want to know which of them are goods, I'm thinking
to buy Dunestar 600 because W3NQN is so high in money and that's hard to
me.

Please tell me your opinions about your bandpass filters and the Dunestar
600.

Thanks!

Att Alfredo Velez WP3C
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