Rick,
go to http://www.arcticpeak.com/radiopages/intermodulationproducts.htm and
plug in 14020, 21020, and 28020 in as the frequencies of the three radios in
your example. Look at the odd order results of the PA mixing products which
WILL occur in close proximity when there is NO bandpass filtering to
attenuate out of band ingress and egress of unwanted products.
Yes, we need to be selective in using the best radios for a multi TX
operation. We also need to provide adequate bandpass filtering so that no
IMD products are produced in the PA and first IF of other on site radios.
73 & DX,
Gary - AB9M
-----Original Message-----
From: Rick - DJ0IP / NJ0IP
Sent: Monday, July 28, 2014 11:50 AM
To: 'Billy Cox' ; 'Discussion of Ten-Tec Equipment'
Subject: Re: [TenTec] THANK YOU AND APOLOGY - for Billy
Thanks Billy, like always, excellent technical data.
A couple of points.
The 40dB is a published spec from Dunestar.
They "claim" :
- Insertion: typical 0.5-,7db,
- Rejection: typical 40db band-to-band
So that's where I got that number. I can send you the spec sheet if you
like.
I was not referring to reducing in-band crud, but rather out of band crud.
In my example, I knew crud would still be transmitted on 40m, but thought
out of band crud would be reduced by 40db (or whatever the actual number of
the filter is). I still think that part is correct.
However I did not consider the harmonic aspect.
The harmonic of the crud is probably still going to be strong enough to
raise the noise level of the other radios on site.
At the end of the day, our only alternative is to be selective on our choice
of radios at multi-TX sites.
I have read Jim's paper on coax and coax stubs.
I have it saved along with several other of his papers.
Tnx agn.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Billy Cox
Sent: Monday, July 28, 2014 6:14 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] THANK YOU AND APOLOGY - for Billy
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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