Labgear CM5220 satellite line amps
 

I bought a bunch of these from CPC yesterday. They were a bargain at about
£2.50 each, instead of the usual £8 or more.

The email from me asking for a returns number reads as follows:

The primary purpose of these amplifiers is to compensate for signal losses
in long cables. Since these losses increase with frequency it is necessary
for the amplifiers to have more gain at the top than at the bottom of the
satellite band. Accordingly they are shown on the technical data sheet as
having gain of 13dB at the bottom of the satellite band, rising to 20dB at
the top end. We have used these amplifiers in the past (although the
physical appearance was different) and they complied with this
specification. The amplifiers supplied on this occasion have (according to
my tests) gain of 21dB at the bottom of the band, dropping to 16dB at the
top. This reverse slope makes them impossible to use because the result
would be highly unequal signal levels.



Bit of a peculiarity, don't you think?



Out of curiousity I went a little bit further than the usual tests. The gain
of these amps peaks at 24dB at about 840MHz. The gain at the bottom of the
UHF TV band is 18dB. Unfortunately the noise rises to an unacceptable level,
on UHF channel 49. Otherwise I would have used them as UHF masthead amps!



On the satellite band these amps have a higher and more uneven noise figure
than the CM5220 amplifiers that I have left over from the last batch.



The new CM5220 appears to be a different (and inferior) procuct to the old
version.



I'll email Labgear and ask them what goes on.



Bill

Labgear CM5220 satellite line amps
 

"Bill Wright" wrote:

... Accordingly they are shown on the technical data sheet as
having gain of 13dB at the bottom of the satellite band, rising to 20dB at
the top end. We have used these amplifiers in the past (although the
physical appearance was different) and they complied with this
specification. The amplifiers supplied on this occasion have (according to
my tests) gain of 21dB at the bottom of the band, dropping to 16dB at the
top. This reverse slope makes them impossible to use because the result
would be highly unequal signal levels.

Bit of a peculiarity, don't you think?

Yes.

I presume that you've made this type of measurement many times before
and know all the gotchas. Network analysers can be *******s. I've often
had trouble enough sorting out a flat frequency response from a
straight-through connection before feeling confident enough to insert
the network under test.

--
Dave Farrance

Labgear CM5220 satellite line amps
 

"Dave Farrance" wrote in message
...
"Bill Wright" wrote:

... Accordingly they are shown on the technical data sheet as
having gain of 13dB at the bottom of the satellite band, rising to 20dB at
the top end. We have used these amplifiers in the past (although the
physical appearance was different) and they complied with this
specification. The amplifiers supplied on this occasion have (according to
my tests) gain of 21dB at the bottom of the band, dropping to 16dB at the
top. This reverse slope makes them impossible to use because the result
would be highly unequal signal levels.

Bit of a peculiarity, don't you think?

Yes.

I presume that you've made this type of measurement many times before
and know all the gotchas. Network analysers can be *******s. I've often
had trouble enough sorting out a flat frequency response from a
straight-through connection before feeling confident enough to insert
the network under test.

Well, I try to keep it as simple as possible. I compare the gain as measured
on two muxes near the bottom of the band with that measured on two near the
top. I usually do this sort of thing several times with different samples of
the unit under test, and with different signal inputs. Comparison between
items is of course easier than trying to obtain absolute measurements.

The other method I use is to have a noise generator as source. In this case
it looked pretty conclusive on the speccy screen when I did it a few times.

None of this is anything like lab standard testing of course but I think if
you're careful and sensible you can reach valid conclusions, at least for
the simple things I need to test.

Bill

Labgear CM5220 satellite line amps
 

"Bill Wright" wrote:

Well, I try to keep it as simple as possible. I compare the gain as measured
on two muxes near the bottom of the band with that measured on two near the
top. I usually do this sort of thing several times with different samples of
the unit under test, and with different signal inputs. Comparison between
items is of course easier than trying to obtain absolute measurements.

Yes, that'll do the job.

The other method I use is to have a noise generator as source. In this case
it looked pretty conclusive on the speccy screen when I did it a few times.

Fair enough.

None of this is anything like lab standard testing of course but I think if
you're careful and sensible you can reach valid conclusions, at least for
the simple things I need to test.

I didn't really engage my brain before typing. I don't imagine that
you'd have one of these in the back of the van:

http://www.home.agilent.com/agilent/...7.536894459.00

--
Dave Farrance

Labgear CM5220 satellite line amps
 

I bought a bunch of these from CPC yesterday. They were a bargain at about
£2.50 each, instead of the usual £8 or more.

As my late Mother-in law would say,

cheap's dear.

Graham.
%Profound_observation%

Labgear CM5220 satellite line amps
 

On Wed, 22 Nov 2006 20:06:04 -0000, "Graham" wrote:


I bought a bunch of these from CPC yesterday. They were a bargain at about
£2.50 each, instead of the usual £8 or more.

As my late Mother-in law would say,

cheap's dear.

Alternatively: "Buy it cheap, buy it twice".

Rod.

Labgear CM5220 satellite line amps
 

"Graham" wrote in message
...

I bought a bunch of these from CPC yesterday. They were a bargain at about
£2.50 each, instead of the usual £8 or more.

As my late Mother-in law would say,

cheap's dear.

Yes, but with a branded item that has a type number you'd think you'd be OK,
wouldn't you? Presumably if I'd bought some of the same amps from elsewhere
at £10 each they would have been, well, the same.

Bill

Labgear CM5220 satellite line amps
 

"Roderick Stewart" wrote in message
...
On Wed, 22 Nov 2006 20:06:04 -0000, "Graham" wrote:


I bought a bunch of these from CPC yesterday. They were a bargain at
about
£2.50 each, instead of the usual £8 or more.

As my late Mother-in law would say,

cheap's dear.

Alternatively: "Buy it cheap, buy it twice".
Or in this case, send it back with a flea in its ear, and complain to
Labgear. I've got some Triax ones and some Vision ones that seem to be OK.

Bill

Labgear CM5220 satellite line amps
 

"Roderick Stewart" wrote in message
...
On Wed, 22 Nov 2006 20:06:04 -0000, "Graham" wrote:


I bought a bunch of these from CPC yesterday. They were a bargain at
about
£2.50 each, instead of the usual £8 or more.

As my late Mother-in law would say,

cheap's dear.

Alternatively: "Buy it cheap, buy it twice".

I prefer your phrase but usually omit the subject 'it'.

'Buy cheap, buy twice'.

Roger R