Forum of sm0vpo http://sm0vpo.wahlberg.cc/ This is an XML content feed of; Forum of sm0vpo : Last 10 Posts Copyright (c) 2006-2012 Web Wiz Forums - All Rights Reserved. Mon, 21 May 2012 05:01:54 +0000 Mon, 21 May 2012 03:50:54 +0000 http://blogs.law.harvard.edu/tech/rss Web Wiz Forums 10.11 30 sm0vpo.wahlberg.cc/RSS_topic_feed.asp Forum of sm0vpo http://sm0vpo.wahlberg.cc/forum_images/sm0vpo2.png http://sm0vpo.wahlberg.cc/ Homepages : New members http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=556&PID=4503#4503 Author: Guests
Subject: New members
Posted: 12-May-21 at 03:50

El centrocampista cataln ha http://www.camiseta-espana.com/ - camiseta de españa  prometido, pese a todo, esfuerzo hasta el final de temporada. "No podemos engaarnos a nosotros mismos ni a nadie. Dependemos de otros, pero si hay una mnima posibilidad, por muy remota que sea, el equipo luchar por conseguirlo",   http://www.camiseta-espana.com/camisetas-de-real-madrid-c-3. - las camisetas del real Madrid ha comentado.

Verd se ha mostrado autocrtico por el partido de ayer. "Ya sea por la ansiedad, por las ganas de hacerlo bien... no estuvimos al nivel que queramos", ha apuntado. Adems, ha extendido esta reflexin a toda la temporada: "Por momentos, en algunos encuentros, nos ha faltado intensidad, concentracin   http://www.camiseta-espana.com/camisetas-de-real-madrid-c-3. - camiseta real madrid 2012 o estar ms metidos".
]]> Mon, 21 May 2012 03:50:54 +0000 http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=556&PID=4503#4503 Questions : question on input impedance http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=639&PID=4501#4501 Author: DragonForce
Subject: question on input impedance
Posted: 12-May-20 at 20:41

Seventh Ice, you really need to do some home study - I'm sure that with a little research all these questions of yours can be easily answered.

Your original questions have now been answered and I think the time has arrived for this thread to be closed.
]]> Sun, 20 May 2012 20:41:06 +0000 http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=639&PID=4501#4501 Questions : question on input impedance http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=639&PID=4500#4500 Author: Ivan
Subject: question on input impedance
Posted: 12-May-20 at 20:26

Hi,
1/ what about doing some auto-study ?
2/ Has your RF amp a symmetrical output ? If not, as I expect, you should not connect a symmetrical antenna directly. Use a balun !
3/ You cannot make difference between forward and reflected power without a directional coupler.
4/ What sort of counterpoise does the whip antenna have ? Seems to be insufficient to me. The antenna radiation may be poor.
5/ If I remember correctly, bypassing the RF choke may cause instability of the amplifier. If the choke is too big, it significantly reduces the output power. I need to remember the schematic, but it is inaccessible now.
6/ A SWR meter can be made by yourself relatively easily and cheap. The most expensive part is a microammeter taken from an old tape recorder or from a battery tester.
7/ Capacitance may stop the amplification or cause oscillations. A parralel confuguration can be used. It will increase the current and power amplification factor primarily.

BR from Ivan
]]> Sun, 20 May 2012 20:26:44 +0000 http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=639&PID=4500#4500 Cool Ideas : MEMORY LANE! http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=656&PID=4499#4499 Author: DragonForce
Subject: MEMORY LANE!
Posted: 12-May-20 at 20:01

I've said this before, but hey!

My first real introduction to electronics was on my 10th birthday, although I was playing with my uncle's soldering iron about 6 months previous to this. 

Dad gave me a yellow book called "Radio", by David Gibson, and we built the crystal set that was published in it.  Of course, it didn't work, we didn't have anything like a decent enough local transmitter.  Dad strung up some 30' of wire in an attempt to get it working, but alas, nothing was received on that little set.

Still, he bought me the book and all the bits for the crystal set plus a brand new yellow Antex model C 15W iron.  I still have a model C, although of course it's the more modern version whereby the handle is a yellow resin, the original was more like a cast yellow bakelite material.  The bits were tinned copper and even Ersin Savbit solder used to bite into the copper forcing me to file the tip until it had worn so much I had to buy another!  I remember once I had to make my own bit! I got a long narrow strip of copper sheet from somewhere - probably from a scrap TV or something.  I folded it round to make a tube and then sharpened the end like a fountain pen nib.  I was quite happy with that for a while.  I remember how it used to catch in the spring of my iron stand and sometimes get pulled off as I took the iron out to use it.  Course, it was a case of switch off the iron quickly, fish the bit out with my pliers and refit it, and then hope the element hadn't overheated.

I still have a copy of the David Gibson book, although the one I have was purchased off Ebay a few years ago.  I've found out since that the two transistor radio published in the book cannot work, and even though the photograph of the built circuit and the circuit diagram agree with other, the radio as was, simply could not have worked.  As for the published superhet design - it used a tripple gang tuning capacitor, very much out of my price range as a 10 - 14 year old boy grabbing old TV sets (and other PCB's) from the local bit of wasteland people used as a dump and stripping out anything that was at all useful.  The old valves made for excellent target practice with a .22 cal Webley air pistol :D

I remember that most of the capacitors I took off those old boards were the ones that nowadays you change on sight - Hunts and RS.  Those yellow boxed axials and the long blue tubular ones rated at 1000 volts.  This could explain why some of my projects built using them didn't work.  Ah well, experience counts I suppose!

There was a local radio shop on Midland Road - owned by a little Jewish lady and a white haired old man.  I remember buying .5W resistors from there, an orangey salmon pink colour they were, and 3 new pennies each.  She'd always make a point of telling me that they were 5% - I suppose the norm at the time was for 10 or maybe even 20%, and 3p was affordable to me back then.  A single BC108 transistor cost me 25p each, and two of those would take all my pocket money, so if I managed to rob one or two transistors from something I found on the dump, so much the better :D  They were lovely people and I am sure they were originally from Germany - of course, this was 1975, I never even knew their names.  I say it was a radio shop but they never actually sold radios as such - just lots and lots of electronic components, and I know they didn't stock Denco coils or variable capacitors and such like.  For those, you had to go into Bristol town centre and visit a shop called Pitts of Picton street.  Just over the road in Cherry lane was Target Electronics - both places long since gone due to places like Maplin, who opened a shop a mile or so up the road.  Pitts was good, all their stuff was high quality and you could smell the phenolic resins as soon as you walked into the place.  One of the window displays they had for quite a while was three pieces of copper clad PCB laminate - one of those sheets was a good square yard in size!  Target used to do bargain bags, and black ferric chloride crystals in double sealed bags.  Mixed with water, it got very hot!

Target had good staff - if you went in with a list of components, the guys behind the counter would know exactly what you going to build with them and would suggest more suitable alternatives if they had anything better than what you asked for (or cheaper, they weren't after a better profit margin).  I remember his name was Robin, and he was a nice guy.  The shop is still there but has been closed since the mid 1990's.  That's the place where I saw my first Nascom computer, they were fault-finding on the sales counter.

Back in 1990 I visited a firm of industrial sign makers.  They also used to make PCBs using a machine router.  They used to use sheets of laminate that were the same size as the perspex panels they made shop signs for - 8x4'.  I've never seen anything like that before.  And yet after they routed it on a machine, all drilling was done by hand.  The gaffer told me that they don't do so much of it nowadays as customers preferred PCB's to be etched rather than machine routed, and they were going to sell off their stock of copper clad boards.  Wish I could have had one!

On from that, I used to cut up old tin cans and make stuff with the tin plate.  I remember it used to drive my mum crazy with worry, since that stuff was sharp, but luckily I never once hurt myself.

Nowadays, I just order all my componets by post, or trawl ebay.  It's a shame that electronics is a declining hobby.  In these days of digital DAB radios, the kids of today have no interest in building a superhet.  Once commonplace comonents now either have to be hand made or sourced from the internet.  I was lucky to find a set of IF transformer coils for 455KHz a few days back - thing is, they ship from Australia, so I hope that they don't attract a load of import duty. 

I can understand Denco going out of business, I can understand why Denco coils attract such high prices on ebay.  BUT, it would be nice if somewhere construction details were available so you could make them at home.  All those old circuits that use Denco coils could then be put to good use again.


Edited by DragonForce - 9 hours 43 minutes ago at 20:17]]> Sun, 20 May 2012 20:01:44 +0000 http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=656&PID=4499#4499 Cool Ideas : MEMORY LANE! http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=656&PID=4498#4498 Author: G8TDU
Subject: MEMORY LANE!
Posted: 12-May-20 at 18:43

Ive still got, and it still works, the wedding present, my mum bought my dad on the black market in 1947, a Graetz Melodica valve radio...its got a fantastic sound, with 3 loudspeakers.

In 1967, at the age of 11, i fixed my first 'wireless' an old Bush, it had a faulty amp valve, this i only knew because when i tapped it, it flashed blue inside and made a noise. I went to the local newsagents and copied the address of a valve company in London (I couldnt afford the 2 and 6p for the Television magazine. A few odd jobs later, i saved up the 7 and 6 plus the 2 and 6 P+P for the orange EBC33 valve, days later i got a silver AR21 valve in the post...confused, i plugged it in, and the radio worked!! The valve came from Z&I Aero Electronics on Tottenham Court Road.
]]> Sun, 20 May 2012 18:43:06 +0000 http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=656&PID=4498#4498 Cool Ideas : MEMORY LANE! http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=656&PID=4497#4497 Author: DragonForce
Subject: MEMORY LANE!
Posted: 12-May-20 at 16:47

Hows about this for a trip down memory lane?

There is a forum for UK vintage radio equiment too!  They do all sorts there, TVs, tape recorders, comms receivers, test gear etc. I've spent a bit of time on both the US and UK based vintage radio boards lately. 

The US based one:  The only thing I find off-putting is the fact that the guys know little or nothing of British built radios (Hacker, Pye, Roberts etc) - but then, it's a US vintage radio board, so that can hardly be a criticism.  There are many guys on there that will bend over backwards to help you if you approach them the right way.

The British board is slightly different - it's more "business like" in its approach.  Whilst I defend the moderators and board owner's) decision not to allow "text talk" or lazy English, I feel it detracts a little from the friendliness of the board overall.  The guys on there know what a Hacker Sovereign II is though - which is a good thing :)

The only thing lacking in the UK forum is a "clubhouse" forum where members can freely discuss things other than radios.  The US based one has such a forum, and it's extremely popular.

Bottom line is, I've joined both these boards, and I find them both fascinating!  It's easy to just lose a few hours reading how some guy got a wooden box full of broken glass and dust and restored it back to the radio it once was - some of these guys on both boards, are restoring radios back to better than new, and its an amazing thing read about. 

I'd suggest that anybody interested in old radios (not just valve sets) should at go and have a look - there's an awful lot there to see and huge amounts of "stuff to learn"

The US based one:   http://www.antiqueradios.com/forums/

The UK based one:   http://www.vintage-radio.net/forum/
]]> Sun, 20 May 2012 16:47:41 +0000 http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=656&PID=4497#4497 Questions : question on input impedance http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=639&PID=4496#4496 Author: Guests
Subject: question on input impedance
Posted: 12-May-20 at 15:08

i dont understand about dipole antenna, when i connect dipole antenna into output of RF amp... the voltage at 0 cm from dipole antena only 100 mV. i don't have SWR meter becouse its very expensive for people at here... so i borrow oscilloscope at lab... and i can't see if that was forward voltage or reflection voltage....

but if i connect into telescopic antenna / whip antenna (50 ohm)... the voltage 0 cm from whip antenna lot bigger.... 600 mV...

i change Re and get the better gain...  clearer picture..... better brighness and color.... but i still need more gain for better range.... i use Re = 0 ohm / bypass.....

when i bypass RF choke ( 12 turn at ferrit ) there was no different at all with amplitude of output.... i little suspicious with my RF choke... looks like i use bad ferrit....  the inductance and reactance too small for this circuit... but when i bypass binocular (with ferrit bead) , there was lot change at output voltage....output voltage lot smaller.... looks like i use wrong ferrit for RF choke.... what do you think? i hope if i use proper RF choke... the gain will be lot better becouse it will produce higher reactance (XL)

what if i try to use 2 transistor at darlington configuration? capacitance at there will make this circuit not linear maybe? what about paralel transistor configuration, just like harry explain at that website? maybe make more gain....

Best Regards,
]]> Sun, 20 May 2012 15:08:16 +0000 http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=639&PID=4496#4496 Cool Ideas : MEMORY LANE! http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=656&PID=4495#4495 Author: G8TDU
Subject: MEMORY LANE!
Posted: 12-May-20 at 12:44

Dragon force recently sent me an email link for an old mains Intercom dated circa 1960's part of another topic that i think Jalex started. Looking at the link, and zooming into the intercom, i saw the good old LT700 audio output transformer, and its matching LT600 something input transformer, in the days of germanium transistors.

This was the link....  http://www.antiqueradios.com/forums/viewtopic.php?f=4&t=193743

Whilst sat pondering, i began thinking back to my younger years...at the age of 12, i bought a TINY radio from Henrys Radio on Edgeware road london for £2.99 this was in the days when the Russians would do anything to get Western money...remember the Moskvitch car!!!.......

http://siberianlight.net/soviet-cars/

Which magazine in the 70's bought 12 of these...11 failed the MOT when they were brand new!

This was the Astrad Orian radio...you dont even get this quality today!

http://www.flickr.com/photos/2104bouboul/6568099615/


So could we have a memory lane trip?, any goodies that anyone wants to post?
]]> Sun, 20 May 2012 12:44:24 +0000 http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=656&PID=4495#4495 Questions : question on input impedance http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=639&PID=4494#4494 Author: Ivan
Subject: question on input impedance
Posted: 12-May-19 at 12:45

Hi,
RF transistors are really fast, they can be destroyed in tens of milliseconds. Open-circuit and short-circuit are equally bad on RF. The best condition is a matched load. Yes, a 50 ohm dummy load is good.

BR from Ivan

]]> Sat, 19 May 2012 12:45:55 +0000 http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=639&PID=4494#4494 Questions : Ac line intercom http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=650&PID=4493#4493 Author: Ivan
Subject: Ac line intercom
Posted: 12-May-19 at 12:26

Hi Jalex, I had a LED or laser link in mind (in terahertz band, not megahertz !!). If you use the 36 kHz subcarrier common in remote controls for home appliances, you can use an integrated receiver with optimized sensitivity and all filtering. Building a one-way digital link will be really easy then.

BR from Ivan

]]> Sat, 19 May 2012 12:26:15 +0000 http://sm0vpo.wahlberg.cc/forum_posts.asp?TID=650&PID=4493#4493