[FARC] HF Gremlins

[Kirk Talbott]

Yep Bob, W3ICF and KA3HJC recommended the cores on the air conditioning 
system wiring but this is not something I can do.  I can run a ground strap, 
though it would require completely rearranging the room which is not on the 
XYL's favorite things list.  Even doing this would still require a ground 
wire to be over 10 ft. long.

I don't have or the XYL hasn't noticed any static or noise on the phone 
system in the house and I haven't had any reports of distorted audio or 
shocks from the microphone and touching the equipment from RF in the shack 
or poor grounding.  But I do notice that sometimes when I touch the PL-259 
connectors on my window unit after working the radios I'll get a little 
static shock which I thought was just the carpeting and dryness in the 
house.  I get these all over the house, not just in the radio shack.

As for the antenna being possibly awkwardly or ill-fashioned like the author 
of my ARRL wire antenna book indicated I don't really believe that it is 
that bad.  Sure it violates some of the dipole antenna rules by not being a 
half wavelength high, and it's in an "L" shape not straight, and it slopes 
to unequal heights.  I've only got so much property and so many high trees 
so a by-the-book antenna for 80 meters isn't really possible here.  In all 
likelihood it is performing as well as it can.  As you can tell I'm a little 
impatient with that but it is what it is.  Add poor propagation to the mix 
and it's absolutely frustrating.

Now, with VHF wouldn't the same grounding or lack thereof cause gremlins?  I 
have had no RF in the shack gremlin manifestations, shocks, or distorted 
audio on transmit even when I had my quarter wave mag mount in the house 
located 5 feet away from the radio.  I don't have it with the Kenwood on 
VHF.  I didn't have it when using a 20 meter dipole mounted between the TV 
tower and roof with PSK31, RTTY, and Packet and with approximately the same 
length feedline.  Of course I wasn't running more than 35 watts either and 
was only using the 20 meter band.

What I find interesting is that transmitting on any of the other HF bands 
doesn't cause the air handler to come on, only 80 meters and not on all 80 
meter frequencies.  If RF in the shack and grounding problems existed 
wouldn't they manifest themselves as gremlins when using all the bands? Of 
course it could be possible and most likely that the RF forward power of the 
antenna is so low on all the other bands that the effect as gremlins is 
negligible.

I could swear that somebody told me that a choke balun had to be up at the 
antenna feedpoint which would be at the top of my TV antenna tower where the 
feedline connects to the dipole center insulator.  That could be done, but 
does it have to be wrapped around a 2 liter coke bottle?  Can it be just a 
couple of loops of wire held fast with plastic ties?

Another interesting thing is that I've had the Kenwood TS-2000 for a year 
now and I've only had the 80 meter dipole and air conditioning problem since 
the late fall, probably November.  My first antenna was a Hy-Gain 18 AVS 
vertical which I used on 40, 20, 15, and 10 meters.  I had no household 
gremlins with this antenna.  Of course the feedline was nowhere near as long 
either, probably 20 ft. for the vertical compared to 75 ft. for the dipole.

I've also heard stories whereby fixing one gremlin problem causes others to 
crop up so maybe I'm lucky that only the air handler comes on.

73
KB3ONM
Kirk


>From: Bob Moroney <windbrkr at erols.com>
>Reply-To: "Frederick, Maryland ARC" <farc at mailman.qth.net>
>To: "Frederick, Maryland ARC" <farc at mailman.qth.net>
>Subject: Re: [FARC] HF Gremlins
>Date: Sun, 10 Feb 2008 12:44:06 -0500
>
>Kirk,
>
>The choke balun that Joe describe could help solve some of your problem, 
>but also keep in mind that even with a perfect transmission line setup, 
>some of the RF radiating from the antenna will be induced into any 
>conductive structure that happens to be nearby.   That includes your body 
>and that of any other person (or pet) nearby, your downspouts, your house 
>wiring, low-voltage control lines to your AC, audio system wiring, etc, 
>etc.  If these items are electrically isolated from ground, they can even 
>have a significant induced voltage while you're transmitting, to the point 
>of someone touching, say, a metal downspout actually getting a jolt.
>
>It's very likely that wiring like the control lines to your AC unit and 
>your phone lines are not well grounded electrically.  Try listening on the 
>phone while you're transmitting, and you're likely to hear a distorted 
>version of your transmission.  You may not be able to fix these grounding 
>problems, but you can buy some ferrite RF choke beads at Radio Shack or RF 
>Connection or the next Hamfest and greatly minimize the problems caused by 
>RF induced into this wiring.  You can clamp some of these beads around 
>existing wiring, but they tend to be most effective when the wire is wound 
>around them for a couple of turns.  The inductive characteristics of the 
>ferrite at RF tend to attenuate the RF energy, but let the lower frequency 
>signals pass.  If you put one of these ferrite beads at the AC end of the 
>wiring, another at the thermostat end and one in the middle somewhere for 
>good measure, your AC remote control problems may go away.  Same for any 
>other such strange, RF-induced behavior in other circuits.   The coke 
>bottle approach that Joe described is another way of "choking" stray RF off 
>of the coax shield, where it can cause the mischief you described.  
>Slipping some ferrite toroids over the coax can also have the same effect.
>
>You can look at an "antenna tuner" as a pacifier for the final output 
>transistors in your Kenwood.  They want to see 50 ohms, period.  Anything 
>else, and they start to heat up, and that's not good.  If you have a truly 
>resonant transmission line and antenna combo at the transmitted frequency 
>then they'll see 50 ohms and dump all their power into the antenna circuit. 
>  If the transmission line and antenna aren't resonant, the "tuner" adjusts 
>the transmission line circuitry as best it can to give the finals 50 ohms 
>and keep them happy, and passes whatever power is left over up the coax.  
>As long as you've got a tuner in the circuit, it will account for some 
>degree of loss of radiated power.  (Thus the "resonant antenna or nothing" 
>school of thought.)
>
>73, Bob K9CMR
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>Kirk Talbott wrote:
>>I've had some interesting revelations about HF this week and a gremlin so 
>>I thought I'd offer them up to the group for some advice.  I've already 
>>had some good answers but I'm looking for a consensus.
>>
>>First of all the station set up.  A Kenwood TS-2000 transceiver, an 80 
>>meter inverted Vee dipole high point about 30 ft..  75 ft. of RG-8X coax 
>>feedline to a window and a 25 ft. RG-8X coax run in the shack to the 
>>radio.  The Kenwood has its own internal auto tuner and I also use an LDG 
>>AT-100 auto tuner.  None of the radios or tuners are connected to a 
>>ground, more on this later.
>>
>>Am I getting out?  In a great discussion with K3ARN and W3ICF about 
>>forward power, reflected power, SWR, antenna resonance, antenna/feedline 
>>impedance mismatches, and antenna analyzing equipment, they offered some 
>>excellent ideas about how to determine where your antenna is most resonant 
>>without using antenna analyzing equipment.  To most of you pros out there 
>>these ideas will seem obvious but to a rookie they were a great help and 
>>their best idea was to record SWR meter readings at various frequencies on 
>>various bands and make a chart or plot of what was going on.
>>
>>What I found was that my SWR was 1.5 to 1 or lower on the 75-80 meter band 
>>frequences of 3.800 to 3.860 MHz. and this without an antenna tuner of any 
>>kind and right in the middle of the General class phone part of the band, 
>>perfect.  Above 3.860 MHz. or below 3.800 Mhz., the SWR instantly climbed 
>>to 2 to 1, 3 to 1 and beyond.  Ok, it's an 80 meter dipole and it works 
>>great on 80 meters, duh.  Now that this works I thought, lets see if I'm 
>>to be rewarded with any other operable band of frequencies by the antenna 
>>gods.  Not to be.  The plot also showed the other HF bands, 40, 20, 17, 
>>15, 12, and 10 meters had totally unacceptable SWR, with readings that 
>>were full-scale off the SWR meter in the radio.  Antenna/Feedline 
>>impedance mismatch. THE REASON YOU CAN'T HEAR ME IS BECAUSE OF AN 
>>ANTENNA/FEEDLINE IMPEDANCE MISMATCH!  Somebody should make a T-shirt with 
>>this on it at the Ham Fest this summer.
>>
>>Now enter the antenna tuner, a device whose real name should be "LIAR."  
>>Sure, the antenna tuner will tune all the bands to a 1 to 1 SWR with the 
>>exception of 40 meters which tuned to a 1.5 to 1 SWR.  Everything is 
>>beautiful, right?  Now I can throw 100 watts at my multi-band antenna and 
>>work all the bands and all my 100 watts will hit the antenna and be 
>>radiated out into the ether.  Nope, not even close.  I can work 75-80 
>>meters 3.800-3.860 MHz. when there is not a good-ole boy with a linear amp 
>>on every frequency, and I can work my neighbors on Ridge Road and in 
>>Frederick on 10 meters.  But generally I can't work anybody with a good 
>>strong 599 signal on 40 thru 10 meters at long distance, and some not even 
>>at short distance.
>>
>>The gremlin.  Ok, I'll settle for 80 meters on HF as long as I can to talk 
>>to somebody and they don't have to struggle to hear me and I'm as happy as 
>>a fly on.....well you get the idea.  So I ramped up the power on the 
>>Kenwood to first 75 and then 100 watts and called CQ and what happened?  
>>The air handler (fan) for my attic air conditioner unit came on.  First on 
>>3.850 Mhz., then on 3.830, and on 3.820 and just about anywhere in the 
>>band where I wanted to work.  Did it do it at 5 watts during my SWR 
>>testing?  Nope.  Was the air conditioning system actually off?  Well this 
>>isn't so clear cut.  The air conditioning thermostat has two settings for 
>>the air handler fan, ON and AUTO, there is no OFF setting.  My thermostat 
>>was set on the AUTO setting and my 80 meters works as a great remote 
>>control.  I did make a contact though while huddled in front of my radio 
>>freezing with the air conditioner running.
>>
>>After mentioning this fact to several Hams, some of whom looked at me as 
>>if I were crazy, thought a moment and then came up with RF ON THE 
>>FEEDLINE.  Where does this come from?  ANTENNA/FEEDLINE IMPEDANCE MISMATCH 
>>was one answer.  Another answer was inductance tripping an on/off relay in 
>>the air handler unit.  Another was in the form of a question. Are you 
>>grounded?  No, I don't have any ground wires going from the radio to a 
>>ground.  Why?  I read in a book that one, most modern houses have properly 
>>grounded electrical outlets such that running ground straps to radios 
>>wasn't necessary anymore and two,  running an excessively long ground wire 
>>could actually serve as a detriment because it would act like an antenna 
>>an bring RF into the shack.  What is an excessively long ground wire?  In 
>>my case it would be 25 ft. or more since my XYL wouldn't appreciate a bare 
>>copper wire running through the middle of my shack's (bedroom/den) floor 
>>over to the window.  I would have to run my ground wire around and behind 
>>furniture along a baseboard.  But the books say ground wires should be as 
>>short as possible.  Give me a number.  One book said 5 feet or less.
>>
>>So, I would appreciate any and all ideas that you may have.
>>
>>73
>>KB3ONM
>>Kirk
>>
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