dbm to volts (humax F2foxT)

"harrogate3" wrote in message
...

Thanks Bill, saved me wearing out any more of my finger ends!

Yes I know, it gets to the point where you can't pick your nose properly
doesn't it?

Bill

"mike" wrote in message
...
Thanks, Bill, it sort of confirms the GDB4 is about as good as I'll get.
Of course a low gain masthead amp can provide the receiver with a better c/n
ratio simply because it takes out of the equation the cable losses. For a
long cable this can be very significant.


The problem is I'm just the wrong side of the brow of a big hill between
me and CP; I don't think I can get any more height on the aerial on my
bungerlow, (it would rip the chimbley off) the hill is crested by loadsa
trees, and I'm subject to very bad interfernce from our continental
partners??? in certain atmospheric conditions.

And I don't expect to last to 2012 to see an improvement.
Well, Heaven will be line-of-sight to Crystal Palace I should think. Let's
hope you've been good eh?


I looked on Maplin's - they sell some but at 4 squid each they look just
like the stuff that I've already got; do you know where I could get some
good ones?

I don't because we always make our own from CT100 and aluminium plugs.

Regarding the general interference problem, I have improved c/n ratios more
than actually seems feasible many times by stacking two aerials, without
doing any sums to provide a particular null. On the other hand the results
have sometimes been disappointing. I wrote this up and it's on my website
somewhere.

Bill

"Mark Carver" wrote in message
oups.com...
On Aug 3, 10:32 am, mike wrote:

I looked on Maplin's - they sell some but at 4 squid each they look just
like the stuff that I've already got; do you know where I could get some
good ones?

The best thing is to make your own, using lengths of CT-100.

Particularly for


"Mike! Mike! Are you all right! (slaps face and applies smelling salts)
Mike, wake up!

Yes I'm sorry, I'll get him out into the fresh air once I can get him from
under the table. Sorry again. It's happened a lot this since he turned 40".

Bill

"Mark Carver" wrote in message
ups.com...
On Aug 3, 10:32 am, mike wrote:

I looked on Maplin's - they sell some but at 4 squid each they look just
like the stuff that I've already got; do you know where I could get some
good ones?

Best thing is to make your own, using lengths of CT-100, and soldered
joints on the Belling Lee co-ax plugs. Better stil, use F-type
connectors, and F-type-BL adaptors where needed. The problem with
most ready made flyleads is they're very lossy, particularly at the
top end of UHF (exactly where Sudbury's DTT channels are).

(Sorry about previous incomplete post, finger trouble !)

Only this morning I went out to an elderly Sony IDTV that had severe
patterning on analogue. Fitting a CT100 flylead cured it. That was the
flylead from the wall to the DTT input. The analogue is fed from a loop out
to the VCR and back. Those flyleads were OK.

Bill

"Bill Wright" wrote in message
...

"mike" wrote in message
...
Thanks, Bill, it sort of confirms the GDB4 is about as good as I'll get.
Of course a low gain masthead amp can provide the receiver with a better
c/n ratio simply because it takes out of the equation the cable losses.
For a long cable this can be very significant.


The problem is I'm just the wrong side of the brow of a big hill between
me and CP; I don't think I can get any more height on the aerial on my
bungerlow, (it would rip the chimbley off) the hill is crested by loadsa
trees, and I'm subject to very bad interfernce from our continental
partners??? in certain atmospheric conditions.

And I don't expect to last to 2012 to see an improvement.
Well, Heaven will be line-of-sight to Crystal Palace I should think. Let's
hope you've been good eh?


I looked on Maplin's - they sell some but at 4 squid each they look just
like the stuff that I've already got; do you know where I could get some
good ones?

I don't because we always make our own from CT100 and aluminium plugs.

Regarding the general interference problem, I have improved c/n ratios
more than actually seems feasible many times by stacking two aerials,
without doing any sums to provide a particular null. On the other hand the
results have sometimes been disappointing. I wrote this up and it's on my
website somewhere.

That's interesting because our communal system relies on a single
conventional Yagi array mounted on top of a 14-storey tower block followed
by huge amounts of amplification. Perhaps if they used a better aerial
followed by less amplification we would get a usable signal on more than one
Mux? Oddly, the signal quality as measured by my Pioneer STB fluctuates
almost by the second between 100% and ~60%. Typically it reads...
100,57,100,63,100,59,100,61, etc.

(kim)

Bill Wright wrote:

Well, Heaven will be line-of-sight to Crystal Palace I should think.

But possibly a little off-beam of the main lobe of the transmitting
antennas' vertical radiation patterns...

--
Andy

Mark Carver wrote:

Better stil, use F-type connectors, and F-type-BL adaptors where
needed.

A problem with that approach is that most F-to-BL/'IEC' adaptors exhibit
pretty appalling return loss figures, often as poor as 9 dB in Band V,
so they upset impedance matching and introduce unnecessary mismatch-loss
and SWR ripple.

The best approach, in my view, is to use a good quality crimp IEC plug,
such as this:
http://www.dastv.co.uk/ViewProduct.aspx?Product=455

The item illustrated is actually made by Cabelcon. It crimps with a
0.360" A/F hex crimper, the same as used for the better quality crimp F
plugs.

The problem with most ready made flyleads is they're very lossy,
particularly at the top end of UHF (exactly where Sudbury's DTT
channels are).

A bigger problem with most is that, despite boasting double-screened
cable and gold-plated bits, the coax braid is pigtailed at each end and
soldered to a single tag on the outer body of the connector (all hidden
under the over-moulded plastic, of course). The result is that they
leak RF like sieves, and let in impulsive interference like buggery.

Ones with properly screened ends are available, but the problem is that
you can't distinguish these from the crap just be looking at them.
There is a standard for flyleads (EN 60966 series, EN60966-2-5:2003 for
IEC leads to 1 GHz), which includes requirements for insertion loss,
impedance matching and screening factor, but it seems, alas, to be very
little used.

--
Andy

mike wrote:

Conversely, to convert dBm to microvolts follow this example:
Snip

You're making hard work of this. To convert from dBm to dBuV in a
75-ohm system just add 109 (or 108.751 if you want to be fussy). The
corresponding number for a 50-ohm system is 107 (106.990 if being fussy).

--
Andy

On 03/08/2007 17:34, Andy Wade wrote:

http://www.dastv.co.uk/ViewProduct.aspx?Product=455

Didn't they watch the Natwest(?) TV advert?

Andy Wade wrote:
Mark Carver wrote:

Better stil, use F-type connectors, and F-type-BL adaptors where
needed.

A problem with that approach is that most F-to-BL/'IEC' adaptors exhibit
pretty appalling return loss figures, often as poor as 9 dB in Band V,
so they upset impedance matching and introduce unnecessary mismatch-loss
and SWR ripple.

[snip]

Thanks Andy, I didn't know that. I've got about a dozen in use around my house
that I fished out of a skip in Holland. Perhaps that's why they were in there !

--
Mark
Please replace invalid and invalid with gmx and net to reply.