Topics

#40m #TVI #DTV #U3S #WSPR Freeview Interference #u3s #wspr #40m #tvi #dtv

Nik
 

Does anyone here have any problems with their U3S interfering with the digital television signal?

I seem to have a problem, on 40M only, where while the U3S transmits the WSPR sequence on 40M, my Freeview box (a current BT Youview+ box, around 4 months old),  the screen goes black with a message about no, or very poor signal.  The wierd thing is this only happens on 40M.  I've tested the U3S on 80, 40, 30, 20, 17, 15, 12 and 10M and apart from the descibed problem with 40M, the Freeview box behaves just fine.

I doubt it's poor shielding, because I'm talking about 2W or less, and the Freeview box is in the living room at the front of the house, the U3S is in the shed at the far end of the garden, and the end fed half wave is strung from the soffit at the back of the house to the shed in a sloper configuration, fed at the shed end.  I'm guessing whatever is causing the problem is coming down the TV antenna feed into the Freeview box.

Stephen Farthing G0XAR JO92ON97
 

Nik, 

You could try winding the free view antenna coax around a ferrite rod or through a ferrite toroid a few turns. This should “choke” any interference from your beacon. 

Regards, 

Steve 

KEN G4APB
 

I recently bought a bt youview box and kept getting that problem and returned it for a refund as i thought it was faulty, I realised now that I was running my U3S on 4m (70mhz)  = 7mhz x 10?? at the time. I wonder now if the youview box has a particular problem with this freq.

73 Ken g4apb 

Nik
 

Choking the feeder is a good starting point.  I'll also open the box and have a look at how/if its shielded too.

Nik M1DOX

Nigel G4ZAL
 

I had the exact same problem with a YouView (Humax) box and a homebrew WSPR Tx at 400mW.
The Youview also had issues with my QRP station.
I fitted a homebrew filter in the TV coax downlead and it has completely stopped all problems on my TV.

The pics should explain it, but it's a small bit of single sided copper clad board with 2 saw cuts.
The inductors are 0.9mm wire, 5 turns and internal dia is 6mm.
Caps are 4p7
Resistor is 1 megohm

The design was originally in a pamphlet available from the Post Office in the early 80's regarding TV problems  - and No, I don't have a copy now !!

HTH

Nigel - G4ZAL


geoff M0ORE
 

Nigel, is this the filter ( appendix 3) that you have in mind. If only I had £1 for every one of these booklets that I handed out when on PO radio & tv interference service duties!!

Geoff ( G8BBN when booklet published)


Nigel G4ZAL
 

Hi Geoff,

Yep, that'd be the one ! - duly saved the pdf for future reference ;-)
Interesting that it suggests 4 turns for the inductor and 1M5 for the resistor - my memory must be fading (damnit).
Anyway, it works as is.
I slip 2 rubber grommets over each coax lead before soldering and they push into a bit of 19mm plastic tube for a neat looking in-line filter.

Thanks.

Nigel (probably G6WAF when I needed the booklet !).

Nik
 

I knocked one up today in the workshop.  Nearest value caps I had were 6.8pF, showing just over 6pf on the meter.  Wound the chokes from .8mm silvered wire, 6mm ID as you suggested.  Soldered it all up, connected it to the aerial input and.....it works a treat.  i tested it up to 37dBm of WSPR (U3S & 5W amp)  and no TV problems.

Thanks for the advice.  The PDF has gone into the archives for future reference.

Nik.
M1DOX

Alan de G1FXB
 

In days of olde....
(pre Astra? / SKY) analogue satellite receivers
, a common sets own Intermediate Frequency was 70Mhz
maybe freeview boxes use similar?


Alan


On 16/08/2019 06:40, KEN G4APB via Groups.Io wrote:
I recently bought a bt youview box and kept getting that problem and returned it for a refund as i thought it was faulty, I realised now that I was running my U3S on 4m (70mhz) ?= 7mhz x 10?? at the time. I wonder now if the youview box has a particular problem with this freq.

73 Ken g4apb?

-- 
Light travels faster than sound this is why 
some people appear bright until you hear them

KEN G4APB
 

I built one of the filters and did some measurements:- the roll off freq is around 220MHz with a loss at 70Mhz of around 20dB. Using the Signal Quality indicators on my brand new Humax Youview decoder it shows a degradation from 100% Signal Strength (no filter in circuit) down to 94% Signal Strength when inserted, so ok on insertion loss but;
the Signal Quality indicator drops from 100% to less than 10% when I run my 1 watt 70MHz U3S WSPR Tx with the filter fitted, with loss of picture and sound to the TV. I did not suffer this problem before so I don't suspect the TV itself. I even built a second filter and ran in series but before the tv distribution amp in the attic. No improvement seen.

It seems an IF of 70MHz is going to be a tough one to cure unless it is seeing harmonics but I have a 70MHz LPF on the Tx already. Additional ferrite blocks dont help either.

Ken G4APB

geoff M0ORE
 

Ken, any filter must be prior to any active devices. The damage has already been done if you place a filter after the amp. Distribution amps are notoriously broad band designed to cover everything from FM broadcast (88 -108 MHz) to UHF TV. Usually in a plastic case as well.

My Humax shows about 95% sig level with a PO HPF in circuit which cures my 2m BCI. 70cm is too close to the bottom end of the TV band (chan 21).

Geoff


On 24/08/2019 09:53, KEN G4APB via Groups.Io wrote:
I built one of the filters and did some measurements:- the roll off freq is around 220MHz with a loss at 70Mhz of around 20dB. Using the Signal Quality indicators on my brand new Humax Youview decoder it shows a degradation from 100% Signal Strength (no filter in circuit) down to 94% Signal Strength when inserted, so ok on insertion loss but;
the Signal Quality indicator drops from 100% to less than 10% when I run my 1 watt 70MHz U3S WSPR Tx with the filter fitted, with loss of picture and sound to the TV. I did not suffer this problem before so I don't suspect the TV itself. I even built a second filter and ran in series but before the tv distribution amp in the attic. No improvement seen.

It seems an IF of 70MHz is going to be a tough one to cure unless it is seeing harmonics but I have a 70MHz LPF on the Tx already. Additional ferrite blocks dont help either.

Ken G4APB

KEN G4APB
 

I have put the filter before the amp (thought I said that). All the other tvs fed from the amp don’t suffer interference, just this Humax box.
2m and 70cms have always been no-no’s in this house anyway, flatten everything.
Ken g4apb 

 

Years ago I had a similar issue.
A basic HPF worked reasonably well,
But the Faraday screen type braid breaker cured the lot.

https://www.qsl.net/g4lna/pages/braidbkr.html

73 de Andy

geoff M0ORE
 

Sorry Ken, I thought that you started with the the filter at the Humax and then tried before the amp later.

I don't know if digital TV's or set top boxes have IF's these days. 70MHz is a common baseband frequency for microwave gear so I suppose it is possible. A tuned 70MHz diplexor type filter might help or as Andy says, a braid breaker. An email to Humax technical dept may say if 70MHz is used in their sets.

I mis-read your post.

Geoff

On 24/08/2019 14:55, KEN G4APB via Groups.Io wrote:
I have put the filter before the amp (thought I said that). All the other tvs fed from the amp don’t suffer interference, just this Humax box.
2m and 70cms have always been no-no’s in this house anyway, flatten everything.
Ken g4apb 

geoff M0ORE
 

Curing TV interference can be a nightmare. A solution for one case may be useless at another situation which appears to be same. If it is in your own house, it makes it easier as you can try many cures. When it is a neighbour who just wants to get your aerials removed, a case of alleged TVI is one path that they follow and refuse to allow any filters to be fitted.


On 24/08/2019 15:09, Andy Brilleaux via Groups.Io wrote:
Years ago I had a similar issue.
A basic HPF worked reasonably well,
But the Faraday screen type braid breaker cured the lot.

https://www.qsl.net/g4lna/pages/braidbkr.html

73 de Andy

M0RON
 

Is it just free view boxes that are affected?
i have a smart tv with freeview and wireless internet built in, fed from a triple boom high gain tv aerial with my end fed random wire less than a metre below it and along the path that the tv antenna points. No problems whatsoever. A friend though has tvi on 40m, he has a tv amp distribution box. 
Andy
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.

KEN G4APB
 

Hi all, 
both of the filters I am using the braid breaker type of high pass filter. I have one right on the input to the freeview box and another in the attic to the input of the tv distribution amp. Every lead out to other tvs has ferrite blocks. The mains in also has ferrite choke and the gain is wound back so not to overload the tvs. I run the Vhf fm radio feed via a separate amp so no interaction there. The tv antenna is an (expensive) high gain (no preamp) on a mast outside the house away from transmitting antennas and i had the cable renewed too at the time of fitting. The mains supply to the freeview box if of the rfi filter type as is the feed to all tx gear. 

Ask Humax for tech advice !!!! They could not even tell me what the dial on the front does or why it is not mentioned in the user guide!!
Duplexer notch sounds a good idea. i need a local rally.
73 ken G4apb 

Nik
 

I bought a braid breaker filter and it did nothing to stop my 40M WSPR obliterating my Humax Youview+ box.  In the recent past I build the one recommended in this very thread and it worked a treat, placed right before the Humax box.

I concluded that not all BB's are equal.  I'd recomment knocking one of these together if you have the parts and are able.

Good luck.
Nik. M1DOX

KEN G4APB
 

I built both BB filters to the PO design shown earlier. one in a plastic box unscreened, and one covered in copper tape to screen it. I measured both responses so I know they are built correctly. If I use UK 70.15250MHz WSPR freq it is marginally worse than the ‘standard’ 70.09250MHz freq, so i shall try a sharp notch filter when i can get one. 
73 Ken g4apb 

 

On Sat, Aug 24, 2019 at 11:43 PM, Nik wrote:
I concluded that not all BB's are equal.
You beat me to it Nik.
If search the web then I see lots of people using ferrite rings as "braid breakers".
To me, a braid breaker is the one with the coupled coaxial loops.
For some reason, I don't see this referred to so I can't point to anywhere useful.
But I guess the usual radio handbooks and manuals would have a chapter on them.

73 de Andy