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RFI from Kenwood TS430S into landline telephone.

Disgwylfa
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RFI from Kenwood TS430S into landline telephone.

I've recently bought an old Kenwood (TS 430S) to use on 11 mtrs and I love it, but I've found that when I TX on anything in that band or similar I get RFI on (of all things) the landline phones in the house. On the triple 5 and thereabouts it gives a shocking buzz on AM, and muffled voice on SSB.

A quick blip of the PTT on a quiet frequency around 14MHz, and 7MHz shows no sign of the RFI, it only seems to be there around 10, 11, and 12 mtrs.

I have two Solarcon A99s set up here, one each side of the house, and probably about forty or fifty metres away from each other, with a SWR (on either) less than 1.3:1 on 27.555. The radio gives the same RFI effect on either of them. I have ferrites on the RG58 and I've tried putting a really good ground/earth on the radio chassis, I've tried powering the radio from a remote power source and making sure the co-ax isn't going right over a phone line or socket. I've tried a low-pass filter. No joy.

I thought the radio was crook so was about to take it back to its source when I tried one last test: on my way through to the car I set it up again and plugged it into a mag mount on the car roof. The SWR was not great so I didn't TX long, but a one second press of the PTT showed there was no RFI - no telephone buzz on AM, no voice on the phone on USB. I then disconnected the coax from one of the A99s and plugged that into the rig in the same location and the RFI was back.

I've come to the conclusion that either the radio is deeply flawed, or my co-ax simply isn't up to the length I'm running (about 16-18 metres) so I was going to get some better quality co-ax like URM67 or similar and try that.

Does anyone have any other ideas what might be causing the problem, or a cure?

Also, if I’m replacing the coax anyway, I want to cut it to an 'appropriate' length so I can get a true SWR at the radio end. I'm going to need somewhere around 20 metres so I want to work out what a good balanced length would be. As I understand it, a full wave, in air, is 10.88m (for 27.555MHz) and if I go for URM67 the Velocity Factor is 0.85. So would I be correct in my calculation that using 23.12 metres (5x half-wave, times Velocity Factor) would give a true(er) SWR at the radio end?

Last and finally - when the shop I bought the radio from did the General Coverage Mod on it, they had trouble finding diode D39 (to be cut for the Mod). They said part of the problem was that there were TWO diodes labeled D39. If they have cut BOTH of them instead of just the correct one, could that be part of the problem?

Thanks in advance

Steve

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Cheers,
Steve
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9/Jun/2009, 3:27 pm

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26fb99
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Re: RFI from Kenwood TS430S into landline telephone.

cant be the radio if it stops when using an alternative whip.my initial guess would be the antrons.they are well known to need a countrpoise/groundplane....rather than buying the expensive kit the word counterpoise means to balance so the A99 being 1/2 wave,mount them on a half wave 18 foot (minimum,longer is better, metal pole).
if your going to upgrade the coax,use the thick stuff or real expensive mini8,something with a good shield and dont worry about length,its just that shorter is less lossy.what i would do for sure is what ever length you buy,get an extra 20 foot to wind onto a footlong peice of 4inch soil pipe.placed before the pl,fitting of the the A99 this is called an RF choke:- and stops unwanted currents returning as stray RF.this is also what your SWR is as seen at the radio so may also reduce your 1.3 too.
look up the ugly balun on the net or see mine at brents mobile disco pics here.
which ever way the phone line runs will be the way its "polarised" to recieved signals i.e vertical or horizontal so if your coax runs parralel to the line try routing down,along at low level then to the whip vertical again.without tuning the a99s to 7,14 mhz it wont resonate(radiate) the txed signal properly like it will on 27.555 anyway so this will not give a clear indication mate.so apart from the cost of new coax,this is cheap and painless. http://www.hamuniverse.com/balun.html
good luck lad.

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laters peeps 73s

Brent 26 Fox Bravo 99

9/Jun/2009, 6:18 pm

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26fb99
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Re: RFI from Kenwood TS430S into landline telephone.

just thought.once youve sorted your rfi probs and considering that youve already got 2 A99s up.to improve your dx capability by loads....co phase the two.imagine if you had 4 set out in a sqare/diamond, on each corner of the house/garden you could feed any one of the 4 or in your case 2, at a time to make a vertically polorised directional array.same as how a horizontal dipole becomes a yagi beam by placing elements as reflector/directors at the correct spacings. Nice....might play around with this on the mobile.

9/Jun/2009, 7:06 pm

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Re: RFI from Kenwood TS430S into landline telephone.

I'm in mourning here. Why do people continue to butcher their 430s when there is a really easy way to broadband them that doesn't involve cutting or damaging anything? It's completely reversible, too. Sounds like the guy didn't have a clue what he was doing. Oh well...

There is nothing wrong with the rig (other than the cut diodes... sniff sniff), it's just that the field strength is too great for the telephones.

Are you a licenced radio amateur? If so, presumably the radio causes problems on 10 metres too, in which case get the phone company out to sort out their crappy equipment - that's the truth of the matter.

You may, however, be able to wind the telephone leads around some torroids at various points to reduce the problem, or just reduce the transmit power. You can do that by selcting the speech processor and varying the mic gain. This circuit acts like a peak limiter and therefore functions well at limiting the power output. Try it whilst monitoring the PA stage current on the meter. (IC position)

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Andy - 26 FB107

9/Jun/2009, 8:43 pm

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Disgwylfa
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Re: RFI from Kenwood TS430S into landline telephone.

Thanks Gents.

Sounds like I might be on the right track, having just ordered a reel of URM67: thick stuff with a decent braided screen (unlike the 'Grannie's Hair' screen on the RG58 I currently have). The Antron I'm using for the Kenwood is on a ten/twelve foot steel mast. I don't have anything higher to hang it on - would it help to bolt a few metres of horizontal copper wire to each side of the mast below the base of the Antron?

Thanks for the tip about the Ugly Balun / Choke too, I hadn't thought of that but it's a possibility.

The idea of a pair of co-phased A99s has crossed my mind too emoticon

At the moment I use one for 11m DX and the other for Muppets, CB and Scanning.... But a co-phased pair is tempting.

- - - - - - - -

As for the better Mod Andy - I'm guessing you're referring to the "white-wire" mod? Apparently it doesn't work with some serial numbers. I gave the guy in the shop a printout of the white-wire mod as it sounded a lot more sensible than the cut diodes solution, but it seem this particular 430 is one of the ones that the mod isn't suitable for. emoticon

I'm curious about the reduction in TX power idea. Thanks for that. I was been told that TX power is fixed in the 430 unless you do another Mod to convert the Squelch to a RF Power control for SSB! I didn't like the sound of that anyway - so I'll be experimenting with the Speech Proc and Mic Gain on a meter into a Dummy Load tomorrow.

I very quickly 'blipped' the PTT on AM on a quiet frequency around 10mtrs and, yes, the same problem on 10, 11, 12 . . but not on 20m or higher.

- - - - - - - -

I've avoided going down the route of using torroids on the affected phone cables, as I want to try address the cause, not the symptom first if I can. My biggest worry is that if it's causing RFI on my phones, is it doing the same for the neighbours? - I like using the 11m band and don't want Ofcom removing my kit after a complaint.

- - - - - - - -

Thanks again

Steve

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Cheers,
Steve
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9/Jun/2009, 10:07 pm

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Re: RFI from Kenwood TS430S into landline telephone.

You say you want to eliminate the cause of the problem, but I think the problem really is the phones. They aren't designed to pick up RF and should be immune to it, but then I suppose we don't live in an ideal world and Ofcom wouldn't be very sympathetic to out-of-band transmissions and possible complaints from neighbours, so your approach seems the best route.

Regarding the 'white wire' mod, I haven't heard of that by that name, so I'll look into it. The mod I was referring to involves carefully removing a couple of wires from connector 10 on the lower board, using a very snall screwdriver or a pin to depress the retaining tabs within the connector body, allowing the pins to be withdrawn. These can be popped back in again if needed. The green wire of the 3 wires is left connected, and I believe this is to inhibit TX on the AM broadcast bands - a good idea to leave this as a safety feature as the filtering is inadequate here and the unit may also be damaged by transmitting in a range it's not matched to.

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Andy - 26 FB107

11/Jun/2009, 7:34 pm

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Re: RFI from Kenwood TS430S into landline telephone.

Thanks for the tips again Gents. and, to put some closure of this thread, ..…

emoticon

I seem to have overcome the RFI issue at last emoticon

The RG58 type co-ax was replaced by really thick, good quality URM67 with a couple of ferrites over the cable and, just for good measure; I created an air-choke/”ugly balun” en-route to the antenna too. Thanks for the links to that one – I used a nine-inch plastic plant-pot (the cable is so think it wouldn’t really wind around anything smaller) and cable ties.

The new co-ax has a core about four times the thickness of the old RG58, and the shielding is braided copper, not the few wisps of Granny’s-hair that was on the original. As I’ve been on a clean-up campaign for the radio, I also put a clip-on ferrite on each of the “pos” and “neg“ leads from the PSU, just in case.

The above knocked the RFI down from a fully intrusive level of noise to a very faint murmur that can really only be heard if you’re listening specifically for it. Originally, the RFI was so loud my wife interrupted a call to come to the shack and tell me about it, now she says she can barely hear any interference even with the radio at full power SSB or AM. As the root cause (excluding dodgy telephone extension leads throughout this house) now appears to be in hand, I’ve put clip-on ferrites on the leads of the most affected phones and, to all practical purposes, the RFI has disappeared.

I’m still curious as to why this started when I ceased using a Ranger 2970 and took to the Kenwood. The only rational explanation is that it was simply a co-incidence that my wife never happened to be on the phone when I was TXing above, say, 50W on the Ranger.

As an addendum I was discussing antenna mounts on the UK FM CB and mentioned that I wanted to raise my base Antron higher when a local breaker kindly offered a 20ft Alu pole F.O.C. The pole has been collected and, hopefully this weekend, the Antron A99 will be lifted to be a full-half wave above ground.

Then maybe it’ll be time to toy with the idea of co-phasing those two Antrons emoticon

although, with my luck and timing, I’ll probably decide to go for a beam antenna at about that point.

---
Cheers,
Steve
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17/Jun/2009, 8:52 pm

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Re: RFI from Kenwood TS430S into landline telephone.

ANDY - The "White Wire Mod" I referred to was, I believe, the same "Connector 10" solution that you mentioned.

A precis of the Mod, as I found it online, follows for general information:

TS430s Transmitter Coverage Modifications:

There are various articles published on the internet which give general coverage transmission modifications for the TS-430S; and in keeping with the provenance of the information, most describe botches of varying horribleness. In particular, there is no need to crush or cut any diodes or resistors.

The main legal restriction signals from the control unit are grouped on connector 10 on the RF board. The connector carries three logic signals: TXI, WRC, and PD, their descriptions being as follows:
TXI - TX Inhibit - out of amateur band.
WRC - TX Inhibit - out of WARC band
PD - Power down (ie, reduction) on 28MHz (for USA

The behaviour of these lines may vary depending on the serial number and country of purchase.

Additional transmitter inhibit signals are derived from the receiver roofing-filter selection logic, on the RF board itself; these being used to prevent transmission in the range 0.15 to 1.6MHz, and to apply additional restrictions in regions where not all WARC bands are allocated.

For M-type transceivers, regional WARC band restrictions can be removed by unplugging the white link-wire on the RF board (see the user manual, p22). Other versions do not have the WARC band restriction components fitted, and so transmit on all amateur bands without modification.

When configured for full amateur use, the transmitter frequency coverage is as follows: 1.6 - 2, 3 - 4, 6.9 - 7.5, 10 - 10.5, 13.9 - 15, 18 - 19, 20.9 - 22, 24 - 25, 27.9 - 30 MHz.

If you require additional coverage, removing the plug from connector 10 enables transmission at full power over the complete HF range from 1.6 to 30MHz.

The source for that Mod was http://www.g3ynh.info/commercial/TS430.html