[TowerTalk] 160M & BC Band adjacent signal Rejection

[K7GCO@aol.com]

    All points below commenting on the circuity used have technical merit 
but:  

     Lets gets down to "Silver Plated Brass Tacks" for high intellectual 
conductivity of what really worked that I described for the level of 
conditions that existed in my case similar to the original problem in a TT 
Post.  If the circuit solution is very simple--all the better.  Actual 
experience with hard cold circuits as I explained just awaits examination by 
anyone to prove or disprove it to determine the winner, who the wise ones are 
and justify all this TT space.  No one has tried what I suggested so far and 
reported on the RESULTS!!  That's what I'm waiting for.  We have had enough 
theory and opinion floating around. Those with great wisdom are usually 
experimenters who can throw a test circuit together and try it.  It solves a 
lot of problems and conjecture quickly.  I clearly explained my results that 
anyone can duplicate.  Have at it. 
             One Test Is Worth A 1000 Opinions   (Old K7GCO Axiom)
I will recap and also give another technique that solved my strong adjacent 
(10 KHz) BC Band signal.  These techniques can be used on 160&80M also. 

KKHI was on 1550 kHz in San Francisco of I think 10 KW power and played 
classical music 24 hr a day.  It had good reception most of the time in 
Seattle.  A station on 1540 kHz 20 miles away on 1540 kHz would tend to 
interfere when KKHI took a QSB dip on 5 different and typical AM radios.  
Perhaps it wouldn't have on the Sangean CC Radio I have now that Art Bells 
sells which is a very sensitive AM radio of fair selectivity.  So is the $65 
GE AM radio with a bigger ferrite bar antenna coil also.  The radio in 
question was a FM/AM 30W stereo with adjustable toroid bar on the back and 
direct connections possible.

I used a 1 transistor pre-amp circuit that gave the necessary gain and 
selectivity to eliminate the interference 10 kHz lower.  I then used a BC 
ferrite bar with Litz wire with a BC variable tank circuit.  A 15' length of 
antenna wire was connected to the top of the tank.  A ground connection and a 
low Z tap connected to the recover directly. The statement that "If the 
addition of a regenerative RF amplifier, or multi-tuned preselector, improves 
adjacent channel interference the receiver would have to be horrible!" is 
without foundation.  The selectivity of this receiver was totally adequate 
for every other listening requirement I had.  It also solved the problem 
without feedback, intermod, attenuator circuits, filters or external power.  
There was a touch of Innovation and simplicity there.  Make use of it where 
ever you can.  Hi-Fi AM radio selectivity can be tuned fairly broad to get 
more than 5 KHz width on each side.  AM stations can be wider if others 10 
KHz away are not close.  I had one that was too wide and the mfg retuned it.  
Now there is more.

I also found another technique I described before on TT and no one ever 
reported to me as trying it.  We need more experimenters.  We have been using 
the wrong antennas for the BC and 160M band for some time.  I never recommend 
anything I have not tried unless the technical foundation is not strong.  For 
proof try this.  Connect the BC radio to the power line for an antenna in 
this manner.  Use a 3 gang BC variable Xc still found in Flea Markets in 
series with a .1 ufd 600V mica.  Connect to the ground side of a 2 wire 110 
VAC line (there is no difference in signal level compared to the hot one) or 
to the 3 wire ground.  Connect directly to the AM receiver.  Try it on 
160&80M also for some surprises.  Peak the variable and it will give gain and 
selectivity you have to experience to believe.  It also solved my adjacent 
interference problem.  I then used an outside ground and the results were the 
same.

Since Radio Day 1 the instruction sheets show a 50-75' length of wire 
connected to the "A" terminal and a wire from a ground connected to the "G" 
terminal.  WRONG!  On the BC Band it should be the other way around or better 
yet forget the 50-75' wire or the external ground.  Use the ground wire of 
the 110 VAC power line through the .1 and 1000 pf variable Xc.  Now have I 
made this concept perfectly clear?  You don't need all that complex circuity 
many seem to think in certain applications when you have the power to 
Innovate and are an independent thinker.  There is more.

I connected a 25' wire to the telephone ground which I think was connected to 
the buried oil tank.  I added a series BC 3 gang variable Xc and connected to 
the coax center lead (not the ground) on my IC-720 on 160M.  I peaked the 
variable for max signal.  On Xmit I got 1.2:1 SWR.  It was just .05 WL from 
whatever the ground resistance was and the variable Xc tuned out the 
inductance of the 25' wire.  Therefore the rig saw about a 40 or 60 ohm 
resistive load.  It was 7 PM in the summer, I called a W6 in San Francisco 
and got a S-8 report.  I told him "I was working him Ground Wave."  I wrote 
all this up in Radio Sporting Mag some 15 years ago.  I also described 
running different lengths of wire 10' high of 65, 130, 260' long and then 
grounding it with a couple of rods.  If 1/2 wave long the ground resistance 
connection reflects back and can be connected directly to the center of 
SO-239 rig input.  If the ground connection is mostly resistive, it's a low 
SWR circuit.  In actual practice ground rod connections are reactive also.  
Adding resonant radials reduces the reactive components.  I'm going to try 1' 
high elevated radials connected to the ground rods next.  Fine tune the wire 
length for low SWR on the low end of the band with the variable Xc shorted 
and use the variable Xc to operate higher in the band.  It's a One Knob 
Tuner.  If the grounded at the far end wire is 1/4 WL or multiple long, it 
reflects back a Hi-Z and I use an L network or Johnson MatchBox to match it.
  
I've also connected a 120' wire to the ground wire 20' off the ground on a 
power line pole in the back yard for a receive antenna.  It worked great and 
was quiet.

This concept is the "K7GCO Grounded Beverage" that is used also to transmit 
on.  If the wire is a 1/2 wave multiple in length on all bands like 137' is 
and is grounded at the far end, it reflects a Lo-Z back to the transmitter 
end--on all bands 80-10M.  No other long wire does that insulated on the end 
and there is no "end effect" compensation length needed for each band 
involved here either.  I get maximum use out of every antenna.  It's fairly 
broadbanded also and about as quiet as a receive antenna can be.  Try 
different wire heights and then try one 1-3' high (insulated fence wires) and 
then laying on the ground (grounded at the far end) using insulated wire. 

Verticals radiate 360 degrees.  Therefore a Beverage that receives in all 
directions would have application.  I have property about 600' square.  I'm 
going to make the top fence wire around it a "Square Beverage" (terminated 
and grounded)  

The surface area of a ground rod is damn small and actually a poor ground 
connection.  It's about 110 sq in.  The recommended and approved "K7GCO High 
Surface Area Grounds" is to bury one of those oil tanks that are being 
removed due to oil leaks starting outside the shack and at 66' and multiples 
from the shack.  This oil tank gives a high number of sq ft surface area 
compared to a ground rod which isn't even a sq ft.  I used the unused gas 
tanks of a gas station was next to where I lived in SD.  Hmmm I wonder what 
kind of an explosion an RF spark inside it would have created if full of gas 
like claimed for the TW800 747?  

Try what I have just described and it should cause a serious review of all 
that high power theory many are sometimes over loaded with.  There is a too 
frequent practice of Doubting Thomas's and Nay Sayers of suggested 
techniques, results found and suggested on TT by various contributors.  They 
never contact the source privately and ask for details but have no hesitation 
to express their doubts on TT.  Mark Twain said "many are experts in 
everything from child birth to reincarnation without ever experiencing 
either."  All claims need examination, I examine all of them and I certainly 
welcome it but I suggest we need less off the cuff critics and more 
researchers and investigators.  Enough theory, who will be the first 
technical researcher to actually try the suggested circuits and techniques 
with the fingers, eyes and ears instead of the vocal and E Mail area?  I have 
coined a new term called "Appliance Critics."  If done correctly the above 
suggestions do work.  Try them

At some time men will stumble across the truth, pick themselves up and hurry 
along as if they knew it all the time.  (Churchill)  Others react violently, 
do an about face and somehow try and pick it apart.  (Old K7GCO Axiom) 
. 
In a message dated 09.05.00 17:30:30 Pacific Daylight Time, 
w8ji@contesting.com writes:
<< > In a message dated 08.05.00 08:20:48 Pacific Daylight Time,
 > w4ef@pacbell.net writes:
 > << 
 >  I thought a Q-multiplier was an active stage - wouldn't it be susceptible
 >  to IMD just like the front-end you are trying to cure? 
 > 
 >  As I recall the Drake R4C had a pretty narrow passive preselector - but
 >  it was still something like 20 to 30 KHz wide (-6dB?? points) on 160
 >  meters - not enough for BC adjacent channel rejection. 
 >  Mike, W4EF. >>

 K7GCO replies:  
 > I believe intermod is created more in stages with a a mixer?  The Q 
 > multiplier as K3BU suggested doesn't have one if I remember right.  A
 > RF preamp only, as frequently used is no different from the 1st RF stage 
used
 > in tube receivers--without a mixer.  Buy cutting it's gain so it doesn't
 > overload the front end of a receiver, is capable of giving greater
 > selectivity before the receiver and is a very good design as I suggested
 > in a previous post.    K7GCO 
 
> If the addition of a regenerative RF amplifier, or multi-tuned 
 preselector, improves adjacent channel interference the receiver 
 would have to be horrible!
 
 The mixer stages or amplifiers ahead of the bandpass filter would 
 have to be severely overloaded, rendering the bandpass filter 
 useless.
 
 If you ever did get that much selectivity in a regenerative amplifier 
 stage, the stability would be horrible. You'd constantly have to ride 
 the regeneration control, as well as the frequency control. Not only 
 that, the shape factor would be poor. Instead of the flat nose with 
 sharply dropping off skirts from a ceramic or crystal filter, which 
 allows the sidebands of the desired signal through without 
 frequency-vs-level distortion you'd have a steep sharp peak with 
 sides smoothly sloping down from that sharp center frequency 
 peak.
 
 I suspect people are actually only adding attenuation and bringing 
 the overloaded stages out of overload, more than actually improving 
 things from additional selectivity. 

 73, Tom W8JI
 w8ji@contesting.com
  >>
Not in this case!  K7GCO

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