[Elecraft] K3/100 -Second floor- no RF ground ??

[Don Wilhelm]

Chuck,

RF-in-the-shack is always antenna related and not transceiver related.  
Unless the transceiver is having some kind of strong parasitic 
oscillation, and that would show up in other ways as well.

You may not notice the RF at low power levels, but when you get up to 
the 30 watt and above level, it is likely to begin to be troublesome.

A ground to Mother Earth is not likely to help - the wire down to the 
ground will have some length to it and where it is near a quarter 
wavelength long, it will present a high RF impedance in the shack, 
exactly opposite of what you are trying to accomplish.

Given your difficult situation, I would suggest that quarter wavelength 
counterpoise wires will be your best choice for creating an RF Ground in 
the shack.  Cut one for each band you will operate - treat the far ends 
just like the end of an antenna, insulate it and keep it out of reach 
for humans and pets.  The far end will be hot with RF when you operate.  
Yes, it may radiate, for it will become a part of your antenna system.  
If you have multiple wires, then try to separate the ends as much as 
possible, they will interact and de-tune each other.  If you can get 
them outside, do so, but they will work run out on the floor of the 
shack if necessary - if you have to do that, I would suggest keeping the 
power low for safety - I would think 50 watts is a practical upper 
limit, but your choice may be otherwise.
Don't forget about the RF at the far end - at higher power levels, it 
can start fires if near or in contact with combustible materials.

An Artificial Ground such as the one from MFJ is nothing more than a 
series tuned circuit with a single wire running from it - it behaves 
just like my suggested counterpoise wires - but it must be tuned to 
resonate with the wire.  If you are planning rapid and easy band changes 
with the K3 tuner, then forget it because you would have to tune the 
artificial ground too.

Your physical constraints will likely dictate the solution that is 
"best" for you.  We all do not enjoy ideal antenna systems.

73,
Don W3FPR

callen1155 wrote:
> Hello guys,
>
> I'm planning on purchasing a K3/100 but am concerned about my second floor
> shack and RF problems.
>
> First of all:
> 1) I don't have an RF ground (don't really want to drill thru the house and
> siding for the ground strap) and 
>
> 2) my antenna is a semi-indoor/attic dipole (HOA).
> I'm running a coax from the second floor radio to the attic where i attach
> to a dipole (no balun) and the dipole runs the length of the house each way
> and out the eaves where both wires run out about 35 yards to the trees.   
>
> I'm using my K2/15 and don't have problems but previously with my old Knwd
> TS 830 at about 100 watts the vibroplex bug would 'bite' me. I'd also get
> some RFI on the TV (didn't try any filters to prevent it).
>
> I know both of the above arrangements are potential sources for RF problems.
> What I don't know is whether RF problems (both the 'burn' and RFI) are radio
> related; i.e. are some radios more prone cause issues and how is the K3/100
> in this regard as compared to the TS 830?  (this may be a non-question-- i
> just don't have enough experience with different radios to know). 
>
> So I'm wonder if any of you operate a K3/100 from a second floor shack, with
> no RF ground, (guess it's too much to ask about a semi-indoor antenna) and
> if you're experiencing RF problems?
>
> Also, if I experience RF problems with the K3 do any you have any experience
> with an "Artificial RF Ground" such as the MFJ-931? 
>   
>