Hi Rick,
Nope ... Re-read what the others have posted,
band pass filters are wide bandwidth filters.
Wide band width filters CAN NOT reduce in-band
narrow "crud" ... they simply cannot by design.
Now let's look at your statement, and see what we
can learn by going a bit deeper on the content:
"... we can reduce all interference (including
broadband noise) by about 40 dB. ..."
A band pass filter (W3NQN, ICE, Dunestar, 4O3A)
will not clean up an IN-BAND dirty TX. What it
may do too is help reduce 2nd harmonic QRM.
Now let's think this out as to it's real impact,
this is NOT limited to contest station setups.
Let's see why the above statement may have value?
Jim, K9YC prepared and published some excellent
TX graphics in the last day showing in-band "crud".
(Yes, it would be great if there was a simple 'cure'
to both in-band and wide-band trash.)
Recall this is a very complex problem, with many
different factors.
1500w out on 7.005 is going still going to be
heard on it's 2nd harmonic at 14.010 when the
antennas are located close to each other.
(Now we also need to measure the amount of RF
going into the RX front end and determining IF
damage could occur, and then preventing damage.)
IF the 7.005 TX is "dirty" as to it's narrow band
crud, it will also wipe out more of 14.010 band area
due to it's wider than needed "dirty" 2nd harmonic
even if reduced somewhat by the band pass filters.
To be clear, by reduced, I mean it's level, not it's
bandwidth. Garbage out is, well ... garbage out.
While there are steps we can take toward resolving
or compensating for much of this, those solutions
tend to be both complex and expensive.
For example, you can purchase (expensive) in-band
filters, that cover say from 14.000 to 14.025, but
that is not really practical as now your station is
limited as to where it can QSY in the band, again if
the TX is 'dirty', even this filter will not help.
As to the "about 40 dB" number, may I suggest you do
some research, we don't need to be shooting from the
hip on this, as the actual numbers may surprise you.
Jim, K9YC did a solid write up for band pass filters,
that has been published in several places, please give
it a review for his actual measured numbers. Depending
on the band, make,and filter design, you may not see
about 40 dB, it will vary, sometimes more, or much less.
http://www.nccc.cc/jug/2013/03Mar2013.pdf
Why is that important? In some cases, it takes both stubs
AND band pass filters to have a suitable RX/TX environment.
One more point, as to having CLEAN narrow signals, is to
consider what I consider "other trash", due to the Pin 1
problems and other challenges within the station as to
taking needed steps against hum, feedback, RFI, etc.
The MPs that Jim and I used several years ago, would have
"other trash" at odd places, like in the monitor, 15m SSB.
One other point, and again this applies to ALL of our
stations, not just contesting setups.
The broad band noise and narrow band crud (my terms) are
a problem for ALL of us. Not a select few.
It's easy think that much of the above does not apply to
our normal stations? Sadly not so ...
Case in point? I believe I read recently where another
ham completed his WAS award using a fraction of a watt.
While that is an outstanding accomplishment, let's look
at it another way ... if we run a piece of equipment that
has both broad band noise and narrow band crud ... at say
the normal 100 watts or with an amp at 1000-1500 watts.
What is the actual level of the noise and crud going out
OUR coax?
It could very well be more than a fraction of a watt! Or
in other words ... we ARE operating QRP/Trash to others.
A few years ago I was on 80m CW tuning around the band and
heard a friend in W0-CO CQing, so I called him. No answer.
Several weeks later we both ended up on 20m SSB, and I asked
him why he didn't answer as he was very loud here in TN.
He told me that evening he was CQing on 160m CW and that I
must have heard his 2nd harmonic. He had just put up a new
80m antenna and yes, it was very close to his 160m antenna.
He THOUGHT the antenna switch was grounding the 80m antenna
when he was on 160m, turns out it was NOT. So the 80 antenna
was radiating the 2nd harmonic from the 160m signal and doing
a great job of it too! Yes, that was quickly resolved!
A tribander for 20/15/10 ... may radiate broadband noise on
all three bands, and those signals in-band will increase by
the same gain as the desired signal.
Our QRP/Trash level just went up by x dB? Not a good thing.
Or what about a mult-band trap vertical? Same challenge.
Many times we tend to place too many antennas too close
and then wonder why they don't work as expected, or as
noted above, undesired/unplanned things happen.
Certain forms of filtering may help. Key word may.
Now, here's an interesting point to ponder, of using an
old technology solution to a new technology challenge?
If you are using a tuner, depending on it's circuit and/or
config ... the tuner may help reduce the broad band noise that
leaves our station, but sadly not the narrow in-band crud.
I don't think it would be too much of a stretch to say that a
tuner, properly used, may also function as a band pass filter?
(The limitations have to do being used as low pass or high pass,
this is why a properly designed band pass filter reduces the crud
above AND below the desired band being used)
My point is ... broad band noise and in-band crud are problems
we ALL need to consider ... and take steps to do what we can.
It's one thing to "think we are clean", it's another to check
it out and be certain or take steps as needed.
How can we do this, especially if we only have 1 rig?
Find a friend who operates HF mobile, offer him or her a cup
of coffee to come over and simply listen in the driveway on
the other bands while you transmit and see what is really
going on out in the yard there.
We owe that to each other to have clean signals and it might
be surprising what you discover.
Yes, certainly we need TX designs in the future to be CLEAN,
(Got that TT?). We know from other brands, it can be done, and
done while using a 12 V PA.
There are some interesting new RF designs to make the TX output
even better ... who will be 1st to offer those in a new rig?
73 de Billy, AA4NU
-----Original Message-----
>From: Rick - DJ0IP / NJ0IP
>Sent: Jul 28, 2014 8:01 AM
>To: 'Discussion of Ten-Tec Equipment'
>Subject: Re: [TenTec] THANK YOU AND APOLOGY - for Billy
>
>STOP - I changed my mind! (hi)
>
>I don't think I was wrong, after all.
>
>Let's be specific now.
>
>STN. 1 is a radio with broadband noise operating on 40m.
>STN. 2 is a K3 operating on 20m.
>STN. 3 is an Orion operating on 15m.
>
>All stations are running 100w.
>
>When STN. 1 transmits on 40m, its broadband noise (over the entire hf band)
>causes the s-meters of STNs 2 & 3 to rise by 3-S-units or abt. 18 dB.
>
>STN. 1 adds a Dunestar Model 300 (40m) Bandpass Filter to his antenna
>feedline. This filter will suppress all signals outside of its bandpass
>(after a specified distance in kHz) by about 40 dB.
>
>THUS the noise being transmitted on 20 and 15m is also reduced by 40 dB.
>THEREFORE the problem originally seen on those two bands at STNs 2 & 3 is
>gone.
>The BPF has successfully eliminated it.
>
>Of course the broadband noise is also transmitted across the entire 40m band
>because that portion of the spectrum is not attenuated by the BPF.
>
>So I return to my original standpoint that bandpass filters will help reduce
>noise level increase on other bands at multi-transmitter stations.
>
>Of course one assumption might be that the noise is being transmitted inside
>the shack, thus not going through the 40m BPF. Fair assumption, but in the
>case I was personally involved with (and solved), that was not the case.
>
>What we found was the noise level varied when we rotated the two beams.
>It was worst when they were pointing towards each other and much better when
>pointing away from each other or off the sides.
>This, BTW, was the reason they were blaming my antennas and not the two
>radios they were using.
>As it turned out, it was both TS-590s causing the problem.
>When the radios were replaced with a TS-850, and then a K2, the problem
>ceased.
>
>Ergo, at least in that case, the broadband noise was through the antenna
>feedline and out the antenna.
>A bandpass filter (which they did not have) would have helped.
>
>Am I missing something here?
>
>73 - Rick, DJ0IP
>(Nr. Frankfurt am Main)
>
>
>-----Original Message-----
>From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Rick -
>DJ0IP / NJ0IP
>Sent: Monday, July 28, 2014 10:01 AM
>To: 'Discussion of Ten-Tec Equipment'
>Subject: Re: [TenTec] THANK YOU AND APOLOGY - for Billy
>
>Yes, you guys are all correct and I was wrong.
>I dunno what I was thinking.
>
>The transmitter's broadband noise will indeed go through the bandpass filter
>because it is also actually transmitting on that frequency too.
>
>My mistake. THANKS for the correction.
>
>So the only help is to filter directly after the PLL, which of course the
>user cannot himself do.
>Buy a new radio, I guess!
>
>73 - Rick, DJ0IP
>(Nr. Frankfurt am Main)
>
>
>-----Original Message-----
>From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Jim Brown
>Sent: Monday, July 28, 2014 8:47 AM
>To: tentec@contesting.com
>Subject: Re: [TenTec] THANK YOU AND APOLOGY - for Billy
>
>On 7/27/2014 11:26 PM, Rick - DJ0IP / NJ0IP wrote:
>> I should have said by inserting a bandpass filter in the antenna line
>> *of the transmitter causing the noise*, we can reduce all interference...
>
>Not quite. Bandpass filters can only kill out of band noise -- that is, a
>20M bandpass filter passes ALL 20M signals, regardless of where they come
>from, but will effectively prevent its own noise from being heard on 30M,
>17M,15M, 12M, and 10M. But it will have NO effect on in-band trash -- trash
>that it generates on 20M, or 20M trash that someone else generates.
>Likewise, a 15M bandpass filter on the 15M rig will prevent it from hearing
>20M trash, but it won't do anything for trash that is ON 15M from a 20M rig.
>
>73, Jim K9YC
>
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