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RF feedback?

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K2QI

RF feedback?

I've noticed that I get some sort of RF feedback spike when using the SB-220
and keying up in sideband mode. It's enough to trip my SWR alarm in my
wattmeter. What is odd is that it doesn't happen on keydown CW. The
problem also gets worse when keying up in sideband mode with mic gain turned
down lower. If I raise mic gaini, the RF feedback isn't as bad and the
alarm doesn't trip as often. Thoughts?

James K2QI
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--... ...-- -.. . .--- .- -- . ...

K2QI

Re: RF feedback?

Thank you Monty, I'll try to isolate the source through elimination as
you've suggested. I'll have to source some ferrite cores for the power
cables. I do have an airwound choke at the antenna's feedpoint, but that
will be replaced shortly with a toroidal choke. Unfortunately, none of the
station components are grounded at the moment. That's something else I'm
working on.

I am curious though; your previous email mentioned rectification of audio in
the wattmeter, feedline or antenna. Could you expound on that a little
bit? I'm wondering how it's possible for this phenomenon to worsen as the
microphone gain is reduced? At a mic drive level of 15 on the K3 and using
the Elecraft hand mic, it rarely trips the SWR alarm. However, if turned
down to 2 or 4, it trips the alarm more often. When turning the mic gain
down to 0, there is no problem.

Also, keying the amplifier when using FSK-D for a continuous carrier shows
no RF spike or anomaly. In fact, I can key the amp using just about every
mode the K3 has and it's fine. This issue only manifests itself randomly
when operating sideband. I can key down on FSK-D and get 1100w carrier with
no interference or issue whatsoever. Even my PC which is directly
underneath the amplifier and does not have any RF suppression works without
problem.

Oddly enough however, I cannot recreate the issue when operating sideband
into a dummy load.

This brings me back to your question about audio rectification; what is it
and how can I isolate/eliminate it? It does not seem at this point to be an
RF issue, or at least RF from the antenna getting into the meter as 1100w
constant carrier does not trip the alarm.

Thanks and 73,
James K2QI

On Tue, Jul 14, 2009 at 9:47 AM, Monty Shultes <[hidden email]>wrote:

> James,
> With all that gear in the RF chain, I would eliminate them one at a time to
> see if the problem goes away. I would also treat all power leads - esp
> SB610 and the SWR meter if it has power - with ferrite beads. I have
> ferrite on the K3 power cable and a common mode choke on the antenna
> coax.for my 80-40 antenna (80 meter half-wave fed with open wire line thru a
> balun).
>
> Good hunting - Monty
>
> The "cheap SWR meter" can be replaced by the K3's SWR meter - that's how I
> check my amp and antenna tuning.
>
> The wattmeter is between the antenna and SB-220. Actually the way I have
>> everything setup is as follows: K3 > cheap SWR meter > SB-220 > SB-610>
>> watt
>> meter > antenna.
>>
>> I forgot to mention as well last night that I cannot recreate the problem
>> when keying down into a dummy load. Only when the K3 is in sideband mode
>> and using the antenna do I get an RF surge. It's driving me batty, so any
>> assistance is greatly appreciated.
>>
>> James K2QI
>>
>>
>> -----Original Message-----
>> From: Monty Shultes [mailto:[hidden email]]
>> Sent: Tuesday, July 14, 2009 7:11 AM
>> To: K2QI
>> Subject: Re: [Elecraft] RF feedback?
>>
>> James,
>>
>> Is the wattmeter between the SB220 and antenna or between the rig and
>> SB220?
>>
>> If the former, sounds like a rectification of audio in the wattmeter,
>> feedline or antenna. If the later, suspect the wattmeter.
>>
>> If not done, bond all units together. This solved other problems for me
>> and
>>
>> maight work for you.
>>
>> Monty K2DLJ
>>
>> I've noticed that I get some sort of RF feedback spike when using the
>>> SB-220
>>> and keying up in sideband mode. It's enough to trip my SWR alarm in my
>>> wattmeter. What is odd is that it doesn't happen on keydown CW. The
>>> problem also gets worse when keying up in sideband mode with mic gain
>>> turned
>>> down lower. If I raise mic gaini, the RF feedback isn't as bad and the
>>> alarm doesn't trip as often. Thoughts?
>>>
>>> James K2QI
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>>
>>
>

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Jim Brown-10

Re: RF feedback?

On Tue, 14 Jul 2009 13:44:00 -0400, K2QI wrote:

>I am curious though; your previous email mentioned rectification of audio in
>the wattmeter, feedline or antenna.

As noted, one or more good common mode chokes are in order. You mentioned the
lack of a station ground. That is a lightning safety issue, but NOT a solution
to RFI.

You didn't mention what your antenna system is, or how far it is from the rig.

The important question is, is this only RFI to the wattmeter, or is something
else going on, like a spur or harmonic? Have a ham nearby listen for spurs (or
take the antenna off another radio and listen for spurs).

Is this an outboard wattmeter, or something built into the power amp? If
outboard, my first move would be to replace the fancy wattmeter with a Bird,
and look for fluctuations indicating increased reflected power. If you don't
see any, I would blame the meter. If you DO still see the fluctuations, I would
look at the K3 and the power amp. The K3 does have some pin 1 issues. Ferrite
chokes would help with that.

http://audiosystemsgroup.com/RFI-Ham.pdf

73,

Jim Brown K9YC

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K2QI

Re: RF feedback?

In reply to this post by K2QI

Hi Monty,

I too have assumed that RF from the antenna was causing the issue, but why
can't I recreate the problem when transmitting a constant carrier?

The behavior of this phenomenon is strange to say the least. What usually
happens is the SWR alarm will activate upon initial keydown in SSB mode.
However, if kept keyed long enough, the SWR reading drops back to 1.1 or 1.2
and operation resumes normally. This drop in SWR usually only takes a
second or two. It's the initial alarm blast that concerns me. When the
alarm trips, I've seen SWR readings higher than 100 to 1, and sometimes as
low as 3.5:1. I can also hear the amplifier relay clicking in rapid
succession.

There is no real pattern as well. The only thing I've noticed is that I can
increase the frequency of tripping the alarm the lower the microphone gain
is set (which to me seems like it should happen the opposite way).

The Elecraft hand mic is connected directly to the front panel. Changing
the bias from high to low has no impact. The SB-610 is an old Heath scope.
Its only connections are 110v in, and RF in and out.

I also put ferrite chokes on the amplifier relay cables that go into and out
of the SWR meter (MFJ-828) and that did not solve the issue. I do not
experience any hotspots in the shack either.

I'll try bonding the components together as well to see if that helps.

Many thanks,
James K2QI

P.S. Apologies to the group for my off-topic problem. There are a lot of
smart guys here though, and I can't seem to get much help from QRZ...

On Tue, Jul 14, 2009 at 4:32 PM, Monty Shultes <[hidden email]>wrote:

> James,
> Not having the problem with a dummy load is revealing. RF from the antenna
> is getting back into the shack and causing mayhem. As I understand it, the
> problem is the SWR meter tripping from high SWR. On the surface it sounds
> like the SWR meter needs shielding and/or grounding. I thinking connecting
> all your chassis together may help even without grounding.
>
> Rectification can occur wherever dissimilar metals meet. I would not
> expect it to increase with reduced audio drive, just the reverse. SWR
> meters have diodes for sensing voltages, and diodes are rectifiers. They
> may be overloaded by the modulated carrier - the modulation has something to
> do with it, as you have no problem with a constant carrier. Is your mic
> connected directly to the radio or through the SB610? I don't remember all
> the functions of the SB610.
>
> Do you notice any current fluctuation in the SB220 when the problem occurs,
> or in forward power? Can you modulate the rig with a computer sound card to
> eliminate RF feedback in the mic as a source?
>
> Monty
>
>

--... ...-- -.. . .--- .- -- . ...

K2QI

Re: RF feedback?

In reply to this post by Jim Brown-10

Hi Jim,
Thanks for the reply. I have not noticed any power fluctuations or
increases in reflected power during the alarm event.

Antenna system is a Tarheel 100A screwdriver mounted on a tripod on my
balcony. The balcony is about 40 feet away from the station. The antenna
is fed with good quality Times Microwave LMR-400UF. The last 20 feet of it
were wound into a common mode choke using 4" PVC. The antenna does not have
a very good radial system; about 10 strands of 20g wire cut to about 12 feet
in length. I do have a 66' length counterpoise but have not laid it yet due
to the size restrictions of the balcony (5' x 12'). The antenna's control
cable was also decoupled via a ferrite choke.

Again, 1100w constant carrier doesn't cause this problem. Only keying up
when the K3 is in a sideband mode. Keying up with drive power from the K3
at 100w or 50w doesn't make too much of a difference; the alarm will trip at
random times. Dropping the drive power to about 12 watts seems to prevent
the alarm from tripping.

This phenomenon does not happen if the amp is off line.
The wattmeter is one of MFJ's new digital/analog deals. It's the MFJ-828.

Please clarify the K3 pin 1 issue; I do not have my assembly manual in front
of me.

73 de James K2QI

>
> On Tue, Jul 14, 2009 at 5:43 PM, Jim Brown <[hidden email]>wrote:
>
>> On Tue, 14 Jul 2009 13:44:00 -0400, K2QI wrote:
>>
>> >I am curious though; your previous email mentioned rectification of audio
>> in
>> >the wattmeter, feedline or antenna.
>>
>> As noted, one or more good common mode chokes are in order. You mentioned
>> the
>> lack of a station ground. That is a lightning safety issue, but NOT a
>> solution
>> to RFI.
>>
>> You didn't mention what your antenna system is, or how far it is from the
>> rig.
>>
>> The important question is, is this only RFI to the wattmeter, or is
>> something
>> else going on, like a spur or harmonic? Have a ham nearby listen for spurs
>> (or
>> take the antenna off another radio and listen for spurs).
>>
>> Is this an outboard wattmeter, or something built into the power amp? If
>> outboard, my first move would be to replace the fancy wattmeter with a
>> Bird,
>> and look for fluctuations indicating increased reflected power. If you
>> don't
>> see any, I would blame the meter. If you DO still see the fluctuations, I
>> would
>> look at the K3 and the power amp. The K3 does have some pin 1 issues.
>> Ferrite
>> chokes would help with that.
>>
>> http://audiosystemsgroup.com/RFI-Ham.pdf
>>
>> 73,
>>
>> Jim Brown K9YC
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
>

--... ...-- -.. . .--- .- -- . ...

Don Wilhelm-4

Re: RF feedback?

In reply to this post by K2QI

James,

Do not overlook the possibility that your amp is developing a parasitic
oscillation.
The behavior will be exactly like you describe - no apparent problem
when driving a dummy load (because it is not frequency sensitive), but
the amp will misbehave when driving a tuned load (like an antenna) which
is frequency selective. When the parasitic starts, you will see high
SWR on your wattmeter. Yes, such parasitic oscillation could be caused
by RF pickup in the amp itself. Your antenna is quite close for 1100
watts power.

I don't have an easy answer for why it only shows up in SSB mode (unless
the amplifier bias is changed when in SSB mode), nor why it is worse
with reduced mic gain settings.

73,
Don W3FPR

K2QI wrote:

> Hi Monty,
>
> I too have assumed that RF from the antenna was causing the issue, but why
> can't I recreate the problem when transmitting a constant carrier?
>
> The behavior of this phenomenon is strange to say the least. What usually
> happens is the SWR alarm will activate upon initial keydown in SSB mode.
> However, if kept keyed long enough, the SWR reading drops back to 1.1 or 1.2
> and operation resumes normally. This drop in SWR usually only takes a
> second or two. It's the initial alarm blast that concerns me. When the
> alarm trips, I've seen SWR readings higher than 100 to 1, and sometimes as
> low as 3.5:1. I can also hear the amplifier relay clicking in rapid
> succession.
>
> There is no real pattern as well. The only thing I've noticed is that I can
> increase the frequency of tripping the alarm the lower the microphone gain
> is set (which to me seems like it should happen the opposite way).
>
> The Elecraft hand mic is connected directly to the front panel. Changing
> the bias from high to low has no impact. The SB-610 is an old Heath scope.
> Its only connections are 110v in, and RF in and out.
>
> I also put ferrite chokes on the amplifier relay cables that go into and out
> of the SWR meter (MFJ-828) and that did not solve the issue. I do not
> experience any hotspots in the shack either.
>
> I'll try bonding the components together as well to see if that helps.
>
> Many thanks,
> James K2QI
>
> P.S. Apologies to the group for my off-topic problem. There are a lot of
> smart guys here though, and I can't seem to get much help from QRZ...
>
> On Tue, Jul 14, 2009 at 4:32 PM, Monty Shultes <[hidden email]>wrote:
>
>
>> James,
>> Not having the problem with a dummy load is revealing. RF from the antenna
>> is getting back into the shack and causing mayhem. As I understand it, the
>> problem is the SWR meter tripping from high SWR. On the surface it sounds
>> like the SWR meter needs shielding and/or grounding. I thinking connecting
>> all your chassis together may help even without grounding.
>>
>> Rectification can occur wherever dissimilar metals meet. I would not
>> expect it to increase with reduced audio drive, just the reverse. SWR
>> meters have diodes for sensing voltages, and diodes are rectifiers. They
>> may be overloaded by the modulated carrier - the modulation has something to
>> do with it, as you have no problem with a constant carrier. Is your mic
>> connected directly to the radio or through the SB610? I don't remember all
>> the functions of the SB610.
>>
>> Do you notice any current fluctuation in the SB220 when the problem occurs,
>> or in forward power? Can you modulate the rig with a computer sound card to
>> eliminate RF feedback in the mic as a source?
>>
>> Monty
>>
>>
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
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>
>

K2QI

Re: RF feedback?

In reply to this post by K2QI

Hi Myles,

The microphone is the stock Elecraft hand mic. There is nothing betwen the
microphone and the rig. I'm home now and doing some more tests and noticed
something odd.

Upon initial keydown in SSB with the amp on and the K3 set to 50w, I'll get
a forward reading on the wattmeter anywhere between 10-17w with no audio
going into the mic. After about a two seconds the forward power will drop
to about .5 watt.

With mic gain set to 0, this problem doesn't occur. Turning it up to 14 or
15, the alarm still trips but not so often. Turning the gain back down to 3
or 4 and the problem occurs with much greater frequency.

There's something going on the minute I key the mic that's looping into the
audio circuitry. Turning the gain down makes the problem worse until I
reach 0 gain.

I also just found something very interesting. If I set the gain to 4 and the
K3 to 50w, I can make the alarm trip. Dropping the K3's output to the
point that I no longer am using the KPA3 (around 12w where the relay
clicks), I can no longer recreate the issue. Cranking back the power so the
KPA3 is used, the problem returns.

James K2QI

On Tue, Jul 14, 2009 at 6:41 PM, myles landstein
<[hidden email]>wrote:

> silly question can you describe your microphone set up are you using
> a stock mic?
> going thru anything between the mic and the rig ?
>
> if you key up on ssb and have the mic gain all the way down and say
> (25-80-100w) does it still occur?
>
>
>
> wonder if you might have a ground loop or some other type of feedback
> entering via the 'audio' chain
>
>
> On Jul 14, 2009, at 6:26 PM, K2QI wrote:
>
> Hi Jim,
> Thanks for the reply. I have not noticed any power fluctuations or
> increases in reflected power during the alarm event.
>
> Antenna system is a Tarheel 100A screwdriver mounted on a tripod on my
> balcony. The balcony is about 40 feet away from the station. The antenna
> is fed with good quality Times Microwave LMR-400UF. The last 20 feet of it
> were wound into a common mode choke using 4" PVC. The antenna does not
> have
> a very good radial system; about 10 strands of 20g wire cut to about 12
> feet
> in length. I do have a 66' length counterpoise but have not laid it yet
> due
> to the size restrictions of the balcony (5' x 12'). The antenna's control
> cable was also decoupled via a ferrite choke.
>
> Again, 1100w constant carrier doesn't cause this problem. Only keying up
> when the K3 is in a sideband mode. Keying up with drive power from the K3
> at 100w or 50w doesn't make too much of a difference; the alarm will trip
> at
> random times. Dropping the drive power to about 12 watts seems to prevent
> the alarm from tripping.
>
> This phenomenon does not happen if the amp is off line.
> The wattmeter is one of MFJ's new digital/analog deals. It's the MFJ-828.
>
> Please clarify the K3 pin 1 issue; I do not have my assembly manual in
> front
> of me.
>
> 73 de James K2QI
>
>
>
>
> On Tue, Jul 14, 2009 at 5:43 PM, Jim Brown <[hidden email]
> >wrote:
>
>
> On Tue, 14 Jul 2009 13:44:00 -0400, K2QI wrote:
>
>
> I am curious though; your previous email mentioned rectification of audio
>
> in
>
> the wattmeter, feedline or antenna.
>
>
> As noted, one or more good common mode chokes are in order. You mentioned
>
> the
>
> lack of a station ground. That is a lightning safety issue, but NOT a
>
> solution
>
> to RFI.
>
>
> You didn't mention what your antenna system is, or how far it is from the
>
> rig.
>
>
> The important question is, is this only RFI to the wattmeter, or is
>
> something
>
> else going on, like a spur or harmonic? Have a ham nearby listen for
> spurs
>
> (or
>
> take the antenna off another radio and listen for spurs).
>
>
> Is this an outboard wattmeter, or something built into the power amp? If
>
> outboard, my first move would be to replace the fancy wattmeter with a
>
> Bird,
>
> and look for fluctuations indicating increased reflected power. If you
>
> don't
>
> see any, I would blame the meter. If you DO still see the fluctuations, I
>
> would
>
> look at the K3 and the power amp. The K3 does have some pin 1 issues.
>
> Ferrite
>
> chokes would help with that.
>
>
> http://audiosystemsgroup.com/RFI-Ham.pdf
>
>
> 73,
>
>
> Jim Brown K9YC
>
>
>
> ______________________________________________________________
>
> Elecraft mailing list
>
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/mmfaq.htm
>
> Post: mailto:[hidden email] <[hidden email]>
>
>
> This list hosted by: http://www.qsl.net
>
> Please help support this email list: http://www.qsl.net/donate.html
>
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email] <[hidden email]>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>
> Myles Landstein
> [hidden email]
> please note my new email address
> dti will soon be eliminated , gmail is my new home update your dir
>
>

--... ...-- -.. . .--- .- -- . ...

K2QI

Re: RF feedback?

In reply to this post by Don Wilhelm-4

Don, if that were the case wouldn't this problem manifest itself during a
constant carrier keydown, and not just in SSB mode?

Anyway, just to eliminate the feedline I took the dummy load outside and
connected the antenna feedline directly to it. I was previously using a
patch cable from the meter directly to the dummy load before.

Testing my system in this confiiguration shows no problems eitther, so it's
not something related to the way I have the coax run or the air-wound choke
I'm using.

Thanks for the information however. I'm not sure if the amp is
oscillating. I recently replaced the parasitic suppressors along with grid
chokes and mica caps and all seems to work fine but I'll keep my eye on it.

James K2QI

On Tue, Jul 14, 2009 at 6:41 PM, Don Wilhelm <[hidden email]> wrote:

> James,
>
> Do not overlook the possibility that your amp is developing a parasitic
> oscillation.
> The behavior will be exactly like you describe - no apparent problem when
> driving a dummy load (because it is not frequency sensitive), but the amp
> will misbehave when driving a tuned load (like an antenna) which is
> frequency selective. When the parasitic starts, you will see high SWR on
> your wattmeter. Yes, such parasitic oscillation could be caused by RF
> pickup in the amp itself. Your antenna is quite close for 1100 watts power.
>
> I don't have an easy answer for why it only shows up in SSB mode (unless
> the amplifier bias is changed when in SSB mode), nor why it is worse with
> reduced mic gain settings.
>
> 73,
> Don W3FPR
>
>

--... ...-- -.. . .--- .- -- . ...

K2QI

Re: RF feedback?

Well, at this point it looks like it may have something to do with the meter
itself. I turned off the peak function and now it works fine without the
alarm going off; even with it set to 1.5:1. Turning the peak function back
on, and blam... alarms galore.

James K2QI
______________________________________________________________
Elecraft mailing list
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--... ...-- -.. . .--- .- -- . ...

Jim Brown-10

Re: RF feedback?

In reply to this post by K2QI

On Tue, 14 Jul 2009 18:26:15 -0400, K2QI wrote:

>Antenna system is a Tarheel 100A screwdriver mounted on a tripod on my
>balcony. The balcony is about 40 feet away from the station. The antenna
>is fed with good quality Times Microwave LMR-400UF. The last 20 feet of it
>were wound into a common mode choke using 4" PVC. The antenna does not have
>a very good radial system; about 10 strands of 20g wire cut to about 12 feet
>in length. I do have a 66' length counterpoise but have not laid it yet due
>to the size restrictions of the balcony (5' x 12'). The antenna's control
>cable was also decoupled via a ferrite choke.

You're running 1.1kW to a screwdriver with essentially no radial system and
you're surprised that you have RF issues? THAT'S your problem! Build
yourself a real antenna. This antennna is a disaster -- it's using every wire
in your house and shack as a counterpoise. No wonder you have RF issues!
Chances are that you're also lighting up every other piece of electronics in
the building.

Screwdriver antennas are designed to work against the body of a vehicle (and
a pretty beefy vehicle at that) as a counterpoise. They are EXTREMELY
compromised antennas. The "choke" you describe is next to useless.

If your can find structural steel on your balcony, you should use that as the
counterpoise for this antenna. The building will still be pretty hot with RF,
but it should work a lot better than what you have now.

>Please clarify the K3 pin 1 issue;

Study the reference I posted.

73,

Jim K9YC

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Don Wilhelm-4

Re: RF feedback?

In reply to this post by K2QI

James,

I did not mean to imply (or state) that the coax was any problem. The
real problem is that you are driving very high power into a small
antenna, and you have not provided a good RF Ground at the base of that
antenna. The net result is that you have high level RF floating on most
everything in the building - the electrical wiring, the building
framework, or anything else that is metallic.

Get a good RF Ground - at least one 1/4 wavelength radial (two opposing
radials is preferred) for every band that you intend to operate and
spread them out symetrically from the base of the antenna. That is step
#1. Unless you do that, please expect many 'strange happenings' from
the high intensity RF Field that you are creating. All that is not to
mention the possibility of human exposure to the high RF Fields. Be
careful.

73,
Don W3FPR

K2QI wrote:

> Don, if that were the case wouldn't this problem manifest itself during a
> constant carrier keydown, and not just in SSB mode?
>
> Anyway, just to eliminate the feedline I took the dummy load outside and
> connected the antenna feedline directly to it. I was previously using a
> patch cable from the meter directly to the dummy load before.
>
> Testing my system in this confiiguration shows no problems eitther, so it's
> not something related to the way I have the coax run or the air-wound choke
> I'm using.
>
> Thanks for the information however. I'm not sure if the amp is
> oscillating. I recently replaced the parasitic suppressors along with grid
> chokes and mica caps and all seems to work fine but I'll keep my eye on it.
>
> James K2QI
>
> On Tue, Jul 14, 2009 at 6:41 PM, Don Wilhelm <[hidden email]> wrote:
>
>
>> James,
>>
>> Do not overlook the possibility that your amp is developing a parasitic
>> oscillation.
>> The behavior will be exactly like you describe - no apparent problem when
>> driving a dummy load (because it is not frequency sensitive), but the amp
>> will misbehave when driving a tuned load (like an antenna) which is
>> frequency selective. When the parasitic starts, you will see high SWR on
>> your wattmeter. Yes, such parasitic oscillation could be caused by RF
>> pickup in the amp itself. Your antenna is quite close for 1100 watts power.
>>
>> I don't have an easy answer for why it only shows up in SSB mode (unless
>> the amplifier bias is changed when in SSB mode), nor why it is worse with
>> reduced mic gain settings.
>>
>> 73,
>> Don W3FPR
>>
>>
>>
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K2QI

Re: RF feedback?

In reply to this post by Jim Brown-10

This is definitely a compromise system, there's no arguing that point but
it's all I can work with at this point in time. I live on the 14th floor of
a NYC apartment building and management will not permit antennas on the
roof. The only place I can put an antenna up is on the balcony. The linear
doesn't get used often; only when necessary to make or complete a contact.

Interestingly enough though, this problem is the only RF related issue I'm
having. I haven't noticed any other problems with my electronics apart from
this. No TVI, no telephone interference, no computer problems or network
issues...

By the way, don't know if you read my previous email but this problem stops
if I turn the peak mode off on the watt meter. The alarm still works and
the amp bypass functions if I pass the predefined threshold in average mode,
but the moment I go back to peak mode this issue returns.

James K2QI

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Jim Brown
Sent: Tuesday, July 14, 2009 9:13 PM
To: Elecraft Reflector
Subject: Re: [Elecraft] RF feedback?

You're running 1.1kW to a screwdriver with essentially no radial system and
you're surprised that you have RF issues? THAT'S your problem! Build
yourself a real antenna. This antennna is a disaster -- it's using every
wire
in your house and shack as a counterpoise. No wonder you have RF issues!
Chances are that you're also lighting up every other piece of electronics in

the building.

Screwdriver antennas are designed to work against the body of a vehicle (and

a pretty beefy vehicle at that) as a counterpoise. They are EXTREMELY
compromised antennas. The "choke" you describe is next to useless.

If your can find structural steel on your balcony, you should use that as
the
counterpoise for this antenna. The building will still be pretty hot with
RF,
but it should work a lot better than what you have now.

>Please clarify the K3 pin 1 issue;

Study the reference I posted.

73,

Jim K9YC

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