Earthing & Radials - RF In The Shack

[trish]

Yes it's that wonderful topic that comes up now and again.. Over the past few weeks (before the cold snap set in) I have been sorting out a reasonable (so I thought) earthing system for HF.. It has meant much digging in the dirt.. Not one of my hobbies, unless it is to plant flowers and the like.. I digress..

Perhaps a bit about the system that I have might not come amiss.. I have a Kenwood TS 680 as the main HF rig. That feeds into a CG 3000 (MFJ-926) via about two metres of RG58 coax. The CG 3000 feeds into thirteen metres of wire that is about fourteen feet above the ground.

When I built the earthing system. I started by banging into the soil, four 22mm copper pipes, to a depth of about five feet. The soil around here is sandy and well drained. Not very good as a ground.. I then planted to a depth of about two inches. Six radials of around nine metres in length. I did add a couple of shorter ones later, for good measure.. All of the radials went to a star point around the copper pipes. The earth to the CG 3000 went to this star point via three heavy duty earth cables that are about one metre long.

So ... Having done this a quick test was made.. All was well up until I tried the 20 meter band. All hell broke loose.. RF in the shack. Computer shut down. The mike clip became hot when it touched me.. Bands above this also had the same effect, although not so bad..

I did a quick check with my trusty MFJ 259 just to see if the antenna was matching as it should do, via the CG 3000 .. That all worked out fine. No problem at all..

The latest attempt to remedy this situation. Has been to run four insulated quarter wave counterpoises to the earth terminal of the CG 3000.. They were cut for 80/40/20 & 10 Metres.. So in theory that should have provided a low impedance on those bands, and get rid of the shack RF .. No chance!!

So ... That's where I am.. I'm toying with the idea of ferrite rings around the coax that is coming out of the CG 3000 .. But I do feel that although that may work. It is covering up a problem, rather than curing it..

Any ideas or similar experiences would be welcome on this... Of course I will report back any further work I do on this.. I don't just give up..

Trish

[bongo]

Hi I wired up the met posts (metal spikes that the fence post fit into)
that go round my garden they seem to work OK!

[trish]

Thanks Bongo.. Nice to hear that you had no problems up North.. Perhaps you have some good soil where you are...

Latest developments - Not a lot really. The weather has been cold, damp, and murky. Not the type of conditions that make you want to go outside digging the dirt so to speak.. I managed to get some suitable ferrite rings and fairly large clamp on units... Three inline clamps + a few turns of coax around a ring.. And .. Yes you have guessed it. No difference at all..

Next phase - One dirty balun made out of twenty feet of coax wound around a suitable former.. No change..

I increased the long wire up to 19 Metres.. No change..

So.. Not one to give up. I rechecked everything. All is fine. Had a word with one of our local experts.. We went through everything I did. He thought that I had covered almost every base, and more.. Next test will be to put the output of the CG 3000 onto a 50Ω dummy load. This might just prove that the CG 3000 is okay or not. If it is fine. The hunt will continue. I have of course put the input lead that goes to the CG 300 onto the dummy load, and all was perfect. No RF in the shack..

A local amateur has a nice manual ATU I will give that a go.. Another thing might be to reduce the aerial wire down to around eight or so Metres and see what happens.. Not that I really want to do this. But the interest of science might just demand it.

The final step that I might take,. Would be to remove the ATU from the shack, and place it at the base of the mast.. It is inside at the moment, and the mast is less than two feet beyond the wall..

Further measures are being taken.. If the weather improves.. I have a T2FD waiting in the wings.. Yes I know that people see them as nothing better than dummy loads with a bit of wire attached.. I like bucking the trend

I won't let this defeat me..

Thanks for listening .. Any ideas most welcome..

Trish

[trish]

Since my last post here. I have done some further work with a friend of mine.. I will try and keep the waffle out of it, so that you can see what we have done.. I will add at this point that further work is ongoing..

(1) Replace CG 3000 with a standard ATU... No change. Matching was easy to get. RF bite and RF interference in the shack was still present.. Conclusion: CG 3000 is okay... Earth might still be a 'floppy' Earth..

(2) Use the four counterpoises only feeding into the ATU earth terminal via an MFJ-931 artificial ground tuner.. Result: Yes we could tune the counterpoises for maximum earth current.. The more current, the greater the RF bite and interference.. Odd that!

(3) Add the earth connection to the above.. No differences..

(4) Add four large ferrite clamps to the coax from the ATU to the TX. The clamps were large enough to put three turns on each.. Result: RF bite virtually eliminated on all HF bands and reduced RF problems.

(5) Take out the CG 3000 and mount that at the bottom of the mast. Add yet another earth spike (four foot long with five inches above ground) Wire that into the four other earth spikes and buried radials in a star form.. Six inches of triple rated earth cable taken from that point to the tuner earth terminal.. One other earth wire taken from that point (about a four foot cable) into the shack to earth the rig at some stage)

Result of the above work (undertaken in cold and wet conditions) was a slight reduction in the RF bite in the shack, and still some interference to other equipment..

So there you have it. I probably have an earth system that others just dream about. I have no doubt that the earth is now a 'stiff' RF earth.. And yet I am still having major troubles.. All my work was double checked and the tuner (CG 3000) was checked out electrically and visually by the supplier..

The very last check I did. Was to connect the separate earth wire directly to the rig earth terminal via the earth tuner.. Tuned that for maximum smoke and the bite and interference increased.. Funny that.. All the theory is saying to me that I shouldn't have had any earth current at all on that lead .. Hmmm

Okay... I know that the few ferrite cores that I used helped a lot.. I am now awaiting the arrival of some ferrite tubes.. I will make up a choke balun using a number of these.. I may use them with RG 58 cable.. I can get a couple of runs through them with RG 58 .. I am toying with the idea of using some RG 178/BU which is PTFE high temperature coax with the tubes.. I can get many more runs through each tube using that cable..

Of course the above choke balun will be placed directly after the tuner, rather than some way along the coax feed..

So there you go.. All fun in my household. This little problem is holding up the other work to get my place looking like a place to live.. But in some ways it is fun trying to resolve problems like this.. The T2FD isn't going up yet.. I may wait until spring to do that.. Or if I succeed with this little problem.. I may just sell it.. If I don't succed.. The CG 3000 will end up on EBAY..

Trish

[trish]

I did say that I would wait for spring before I would do anymore work in the little problems I have regarding earthing and RF in the shack.. The reasonable weather has allowed me to do some work on my system.. So here goes...

Before I talk about the HF setup. I would like to say a little bit about the Tri Band Colinear (GP15) for 6/2 & 70 cms ... I did have it mounted on a pole at around 17 feet by the side of the house.. So some of the signals had to go through the upper level of the house.. That has now changed, and some thanks for it should go to Geoff. Who I met at the Kempton Rally and he gave me some UR 67 cable, so I was able to use that for the new location of the aerial...

In the old location. I had some troubles getting enough power out from the Kenwood TS2000 on 70 cms. It would foldback to about 15 watts from the 50 watts it should produce. The measured swr was within reasonable limits at about 1.5:1 .. Odd that..

In the new location, which was just above the chimney by about six feet and within eight feet on my TV aerial, and that of my neigbours. Was the only place I could put it.. So that location meant that the aerial was in clear air and the results proved that it was worth getting it done..

Local beacons on 6 Meters improved by three S points. Two Meters was even better, at around five S points. The same improvement was found on 70 cms..

The SWR on the GP15 at 6 Meters went from 1.5:1 to 1.8:1 at the centre frequency that I adjusted it for using the MFJ 259B (this tool has saved me much grief, and has made adjusting aerials a dream) but it was within the range of the TS2000 Autotuner.. Two meters and seventy cms also showed a slight worsening of the SWR.. The good news came in that I could get the TS2000 to output 50 watts on seventy.. Don't ask me why it worked, even though the measured SWR was worse.. It just worked.

Now for the HF ... I made up a choke balun using ten ferrite tubes (4s2 mix) and thin PTFE coax using five turns on each tube and put the whole lot in 1 1/2 inch pvc tube.. This further improved the RF situation in the shack.. Sadly when I used the system on 80 Meters using just ten watts, it fried my ADSL modem.. Grrr! So I still had a serious problem.. Next step.. I opened the CG 3000 autotuner and put in two 1 mH chokes and 2200 pF disc capacitors in the supply lines... RF is now a thing of the past... I do ask why the manufacturer hadn't done that themselves.. I would have thought that would have been something pretty basic and essential..

Now comes the Terminated Folded Dipole (T2FD) ... I know that it has been slagged off by people, especially on Eham.. That didn't stop me picking up a brand new Diamond WD330s for a song.. I have a small garden, and I could only dream about a 'real' aerial.. But this one is just 10 Meters long.. So in it went.. I arranged it as a sloper. Six up feet at one end, and twenty feet at the other, with a well placed tree at the centre point, that I used to feed the coax down from.. I also put a choke balun (as I did with the CG 3000) in the coax about five feet away from the aerial..

Now the results.. I measured the SWR using my MFJ 259

1.9 Mhz = 3:1
3.6 Mhz = 1.7:1
7 Mhz = 1.15:1
10 Mhz = 2:1
14 Mhz = 1.7:1
18 Mhz = 1.5:1
21 Mhz = 1.7:1
24 Mhz = 1.5:1
28 Mhz = 2:1
30 Mhz = 1.7:1

Not bad .. The almost 1:1 result at 7 Mhz comes as no surprise, as it naturally resonates at that frequency...

I did some comparisons to the long wire, which is just over 20 Meters long.. And yes.. I could hear that the T2FD wasn't as good on 160 & 80 as to received signals I would say that it was around two to three S points down on the long wire.. But what was astounding.. The local QRM went down to virtually nothing.. So what I was hearing, was an awful lot clearer than before.. So the effective s/n ratio was making up for the indicated lose by a long way.. The only band that I don't see any real rejection of local QRM is 20 Meters.. Something to think about ..

As I also expected.. Results for 40 meters and above was better than the long wire... I did some tests on all bands with some local stations, between the two aerials on transmit.. They couldn't detect any difference on all bands..

The sad part about the T2FD is that it doesn't work at all well on my local radio station on 198 Khz ... So I will be keeping the long wire and feed that into the TS2000 RX antenna input ... But that won't happen until I have done further tests with the T2FD and decided what one to go with.. So far the T2FD is winning.. It tunes up using the TS2000 autuner on all bands without any problem, and no RF at all is coming back down the coax..

Thanks for reading this. I would be interested in the experiences of others..

Trish

[n6ommphil]

Hi Trish,

Thank you for your posts on earthing, as I have been researching this topic because I have RF in my shack, as well... My situation is dire, however, because my wife has a pacemaker! As soon as we became aware of the RF affecting her, my station has been "silenced" and grounding is the highest priority, as you could well imagine!

I appreciate your comments and have learned a lot from reading them.

The only antenna that I have up is a rotatable tri-band dipole (actually, the driven element from a Mosley TA-33jr), but I am building a 75m and 40m trapped, wire dipole, which I hope to have up this fall.

Well, anyway, it took me so long to become a member of this forum, so I could post that I feel strange posting, and hope you don't think I am out of place doing so. Thanks again for your writings on earthing, as they have encouraged me and instructed me, as well...

Phil