Safe distance between antenna and radio

[Jim444444]

Was hoping to mount an end-fed half wave on the outside wall about 10 or 12 ft away from the radio, but worried about RF feedback. Will only be running QRP on HF bands will it be ok.

[ch25]

It will be just less RF.

[InTheClouds]

Difficult to answer with precision, however if you provide counterpoise wires and make your coaxial feeder a little
longer than you need and do an 8 turn choke at the feed point it will reduce the chances of CMC coming into the shack.

https://www.hamgoodies.co.uk/ft240-31-ferrite-toroid

"8 turns of RG8mini/RG58/RG316 (400w SSB) or RG142 (1kW CW/Digi) make a great "resistive" balun/choke for 3.5MHz-30MHz. "

With the wire running parallel against the external wall you may possibly experience some tuning/SWR troubles, and a rather odd radiation pattern so bear that in mind as well. As in possibly more directional and unless you are very high up a high angle of radiation.

Or do you mean attached to a rear facing wall and going down the length of your garden ? (altogether a much preferable approach)

If you gave a bit more detail would help provide a better answer.

[paulears]

If the radio has good enough design to prevent the RF output section not leaking into the preamp and audio stages inside the metal case, where separation is measured in mm, the RF field from an antenna metres away is far less, if not no concern. I’ve never been cautious to this extent ever. You learn from making mistakes, that’s part of the fun. Try everything and see is my motto! Discovering bad design and the limits you need to follow just help you explore the operating envelope. I had back in the 80s a Kenwood with some poor screening and using a random length of wire tuned with an ATU made it warble. Not talking it up quite so much let you get away with it.

[InTheClouds]

That is one way way of looking at it Paul and each to their own way of enjoying things. It is interesting that there does seem to be a distinct "see what happens with some wire" vs have a "efficient mono band antenna" approaches.

With 10Watts (looking for phone/voice contacts only - not digital modes) I knew I needed to make every Watt count so I went for as efficient antennas as I could for the DX bands from the outset. (I genuinely wanted to see what is achievable with a very good antenna and QRP, this way I can build on what I had learnt) That meant plenty of counterpoise/radials or a plain old horiz/V dipole. In what were typically poor conditions I made 1 intercontinental contact on 10W, other than that the most distant contacts in Europe were Greece/Bulgaria on 20m. Foundation legal limit of 10W and relatively poor conditions on 20m and 40m recently mean you need an efficient antenna with a nice radiation pattern to make the most of the available DX. It can surprise you with 10W and I bet when the conditions are good and there are a few more sunspots 10W can work nicely.

Never been into the idea of "multi-band" random wires with strange radiation patterns the higher you go personally.I enjoy the 1 band 1 efficient antenna approach.10W at the seaside would work nicely for dx, you lose all of the ground losses you get with an antenna above soil and your RF is reflected back into the sky along with that nice clear view to the horizon, not to mention the same benefit on RX.

One bit of advice I can suggest, despite getting all my permitted 10W into the sky I could call CQ for hours with no reply. I had more luck responding to others calling or dropping my call at the end of an existing QSO. I just was not seemingly getting heard calling CQ on 10W, or the Euro stations were not interested in speaking to another Euro station and wanted "real DX".

Having a poorly performing antenna on 10W is going to potentially mean a need for extremely high patience and some disappointment. (Unless the sunspot count ramps up fast)

[Jim444444]

Difficult to answer with precision, however if you provide counterpoise wires and make your coaxial feeder a little
longer than you need and do an 8 turn choke at the feed point it will reduce the chances of CMC coming into the shack.

https://www.hamgoodies.co.uk/ft240-31-ferrite-toroid

"8 turns of RG8mini/RG58/RG316 (400w SSB) or RG142 (1kW CW/Digi) make a great "resistive" balun/choke for 3.5MHz-30MHz. "

With the wire running parallel against the external wall you may possibly experience some tuning/SWR troubles, and a rather odd radiation pattern so bear that in mind as well. As in possibly more directional and unless you are very high up a high angle of radiation.

Or do you mean attached to a rear facing wall and going down the length of your garden ? (altogether a much preferable approach)

If you gave a bit more detail would help provide a better answer.

Bit more detail here

Untitled.jpg

My radio will be located in the spare room upstairs about 5 foot from the window. The antenna feedpoint will be mounted outside the window on the wall about 18 ft. above ground and the wire will go straight out up the garden in an inverted v configuration.

[InTheClouds]

RF Feedback, "in the shack " etc. is not specifically related to the distance of your radio from the antenna. If we separate 2 possible causes of "self RFI" the coax length may have influence on some installs in some situations but beyond the scope of my reply.

1) Common mode currents (CMC) on the outer braid of the coax, can happen with your antenna 20m away, as well as 3m away. The solution is counterpoise or radials or an RF choke (of which there are numerous kinds) For a permanent home QTH install and RF earth is also important as I am sure you have been reading about or have studied. Though what you are suggesting with your feeder into a upstairs room will make an RF earth rather difficult to implement, as clearly earth rods and thick, short copper braid cables will be difficult as you will have a long braid going to earth (by being on second floor)

2) Direct coupling "pickup"of RF into a circuit where RF energy is not meant to be.

In 1) we typically get CMC if there is an imbalance on one of the legs of a dipole or if an end fed antenna has insufficient counterpoise/radials. This means return currents have no alternative but to use your coaxial cable as a return path to complete the antenna circuit. I made a DIY antenna which I got a zap off the aluminium VFO knob - ouch ! There is a reasonable chance the audio would not sound great as well (never tested that as I was really just tuning the antenna) I have reasonable amount of radials but either not enough or I need to choke the coax off... refining this antenna is a work in progress.

2) is more likely caused by your radio having a too strong RF field strength nearby coupling directly with some of the radio's circuitry
which is not meant to have RF energy in. As Paul mentioned such as your mic preamp circuit (or mic lead) as an example.

You could get either and most likely neither (with 10W)...and you really need to try it to find out. As I am sure you are aware feeding from the other end of the wire might be preferable...but only try that if you have a problem. With 10Watts you are less likely to encounter any troubles as you are operating with significantly lower RF energy levels... so try it and find out and then report back for further suggestions if there is a problem.

Good luck.

[InTheClouds]

Actually come to think of it maybe someone can answer.. why don't the common ham antenna the "end fed long wire" (and similar antennas EFHW etc.) not generally have counterpoise ?

[Jim444444]

Actually come to think of it maybe someone can answer.. why don't the common ham antenna the "end fed long wire" (and similar antennas EFHW etc.) not generally have counterpoise ?

I'd like to know, if a DC grounded EFHW antenna mounted on top of a 20 ft. aluminum pole or being mounted to a satellite bracket on the side of the wall at the same height, but with a ground wire running from the bracket to an earth rod dug in the ground. Would both setups be considered as counterpoise for the antenna ?

[Buick Mackane]

May have already been mentioned, A long wire needs a counterpoise, If you don't connect one then the shield of your coax will act as the counterpoise, And that means RF flying around your shack unless you fit a line isolator, If a separate counterpoise is used then it needs to be a 1/2 length at the lowest frequency you intend to use, And if you use an earth it needs to be a direct earth, Not via a long connection.