On Fri, 24 Jan 2014 20:25:42 -0500, Jerry Stuckle
wrote:
On 1/24/2014 7:14 PM, Jeff Liebermann wrote:
On Fri, 24 Jan 2014 13:04:48 -0500, Jerry Stuckle
wrote:
The easiest way of seeing it is looking at the output of both tube and
transistorized transmitters on a spectrum analyzer. You will see much
more hash on the transistorized transmitter.
Amazing. You might see more hash with a synthesized transistor
xmitter, but for crystal controlled, they noise is quite a bit less
with transistors.
You obviously don't use a decent spectrum analyzer.
I've never seen or used an indecent spectrum analyzer. These are
admittedly antiques, but do a tolerable job for most things I need:
http://802.11junk.com/jeffl/pics/home/slides/test-equip-mess.html
I wouldn't mind owning a much better spectrum analyzer, but I can't
justify the expense. If I need one, I can usually borrow, or if
really desperate, rent.
Sure - WITH DUPLEXERS. I did it WITHOUT DUPLEXERS. A HUGE difference.
But obviously one YOU DON'T UNDERSTAND. Do you even know what a
duplexer is? (I really doubt it).
I've been fairly polite up until now. I've tried to correct your
mistakes, but have never stooped to personal insults and accusations.
You don't seem to know how to engage in a technical discussion without
being insulting. No more nice guy.
I've designed two 900 MHz commercial duplexers used in wireless SCADA
systems. I've tuned probably around 50 assorted duplexers for a
mixture of ham and commercial users. My only failure was when a local
ham machined a rather nice looking duplexer out of 6" stove pipe, and
then wondered why it didn't work as well as the silver plated variety.
In my spare time, I'm trying to improve on the bad joke of a duplexer
found in the Motorola MSF5000 UHF repeater.
http://802.11junk.com/jeffl/K6BJ-MSF5000/
Yes, I think I know what a duplexer is.
Yes, nowadays, there are transistors with lower noise figures. But they
are relatively expensive, and you won't find them in the less expensive
receivers.
Rubbish. pHEMT devices are available with 0.75dB NF at 1GHz for under
$3/ea. For example:
http://www.minicircuits.com/pdfs/PSA4-5043+.pdf
Note that this isn't just a single device but a MMIC amplifier capable
of belching 100 mw (+20dBm) with 1dB gain compression.
Which you don't use in the front end of a receiver. But I see you don't
understand anything that's been said in this thread, so no surprise there.
Actually, you do, but I picked an example that could be used in a
transmit chain, which I believe was the topic of discussion.
No, AGC will not "try to keep the S/N ratio constant". It tries to keep
the output of the IF constant. As the signal increases, the noise will
decrease, improving the S/N ratio. But you also don't seem to
understand how AGC works.
I stand corrected. The rest of what I said about AGC is correct.
Even back in the early 70's, commercial tube VHF radios could easily get
.15mv for 20db S+N/N ratio. Not much different than the transistorized
versions today.
I think you might mean 0.15 uv/12dB SINAD. A 0.15mv receiver would be
considere comatose.
No, I mean 20db S+N/N ratio. The equivalent SINAD would be somewhere
around .12mv (or a bit less). Not at all "comatose".
Please fix your abrevs.
http://physics.nist.gov/cuu/Units/prefixes.html
I never saw any tube receivers with 0.12µV/12dB SINAD sensitivity.
However, that was at UHF. I don't recall the numbers I was getting
for VHF and low band tube receivers. I could probably excavate some
old Motorola Research line manuals and see what Motorola specifies in
the manual.
That must be because you were working on GE Pre-Prog. I worked with
both Motorola and RCA sets (plus a few others which weren't quite as
good). We were able to get them to .15mv. on VHF.
The radios in the repeater rack are all Progress Line, not Pre-Prog.
No experience with RCA, but the Motorola 5V, 40V, 80D and 140D were
much the same as the Progress line radios. The UHF (T44) versions
started out at about 0.5µV/12dB SINAD and slowly deteriorated to about
1µV. VHF receivers were somewhat better than that, but I don't recall
the numbers.
But then according to you, such a radio would be "comatose". I wonder
just how bad your GE's were?
The comatose was in reference to your abuse of the SI prefixes.
1mv/12DB SINAD is terrible. Such a receiver would never have left our shop.
Please fix your abrevs.
http://physics.nist.gov/cuu/Units/prefixes.html
0.5mv wouldn't leave our shop, either.
Please fix your abrevs.
http://physics.nist.gov/cuu/Units/prefixes.html
And both Motorola and RCA rigs
would hold their sensitivity for much longer than that, even in a mobile
installment.
It was worse in repeater service, where we had to cram 3 repeaters in
a rack because of limited floor space. Note the big squirrel cage
blowers on the bottom of the rack.
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/Santiago-01.html
Mobiles had to be retuned about once a year to maintain optimum
performance. TX output tubes would last about 3 years. (6907 for GE
and 2C39 for Motorola).
Somewhat later, in the 1970's, I found myself designing marine radios.
Typical VHF sensitivity was about 0.25uv/12dB SINAD using a dual gate
MOSFET front end such as a 40673 or 3N212. We ocassionally used
JFET's such as a U310 but the sensitivity was about the same.
Yea, one of the shops I worked at sold similar quality rigs, mainly for
those who wouldn't pay for a good RCA. The Motorola shop didn't sell
anything else, of course.
Interesting. I mention the front end devices and you immediately
deduce everything about the product, the quality, and maybe even are
able to guess the manufacturer? Wanna take a guess? You can even
Google for the right answer without much difficulty. We were making
marine radios in the USA for about 15 years. It wasn't the lack of
quality that eventually killed the company. It was competition
initially from Japan and later from China. Of course, you must prefer
the current level of quality from China.
Maybe in your designs, but not in the ones most of our clients demanded
and paid for.
You designed radios? Good to know. Our radios were used by the USCG,
tug boats, inland waterways barges, bridges, and cruise ships. Those
types of customers don't tolerate failures very gracefully. We also
offered a lifetime warranty to underscore the point. Resurrecting 10
year old radios was not fun, but that's what it took to stay in
business.
Incidentally, my best day was when I visited the USCG repair depot on
Yerba Buena Island, and saw a rather large pile of Motorola Modar
radios. When I asked, I was told those were the one's they couldn't
fix. We just smiled and continued the tour.
Incidentally, have you found the maker and model of the F connector
that your un-named distributor will only sell to "professional"
customers? It was in your office the last time you offered to find
it.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558