K.P.S. Kang's Pixer Superhet

K.P.S. Kang (VU2KR and VU2OWF) has been contributing ideas and circuits for many years from his QTH in Punjab India.  He is the source of what became known as the VU Transmitter circuit:
http://www.zerobeat.net/g3ycc/week1.htm

Today I spotted a recent blog post by OM K.P.S. on a simple superhet receiver he is working on.  He has a knack for describing the design considerations (needed gain, IF selection, etc.)
Check it out:

http://smallwonderqrp.blogspot.com/2016/04/pixer-empirical-hf-superhet-receiver-i.html

and

https://plus.google.com/111066147552844651495/posts

WSPR Party Balloons Make it Across the Pond

		Hans Summers April 15 at 11:25am
VE3KCL/QRP Labs S-9 balloon finally reached Europe! What a crazy way to cross the Atlantic. Crossed Portugal, now into Spain. France is next! 16mW 30m WSPR signal was reported in ZL and VK (19,000km DX). Who says you need 5W on HF WSPR? 73 Hans G0UPL http://qrp-labs.com

My Kind of Math! The Wooden Fourier Transform Machine

fourier analiser from Gymnasiumnovum on Vimeo.

Mixer math with plywood and gears.

http://www.instructables.com/id/Plywood-Math-Machine/

http://hackaday.com/2016/04/11/fourier-machine-mimics-michelson-original-in-plywood/#more-199177

http://hackaday.com/2014/11/18/harmonic-analyzer-mechanical-fourier-computer/

VE3KCL Balloon makes "several loops around Greenland"

Oh, I really want to do this.  We had a bunch of balloons for my daughter's birthday and I found myself trying to guestimate how much they could lift.  There is a balloon store that sells the metalized party balloons used here.  They have a helium tank.   I hate to be a party pooper (!) but wouldn't the antenna represent a bit of a hazard?  If it came down in power lines, that wouldn't be good right?
In any case, three cheers for Dave VE3KCL and for Hans, G0UPL, the wizard who makes the QRSS/WSPR transmitter that is currently flying over Iceland.  

Hi all

Some of you must have seen this already - but the rest of you may find it interesting. Dave VE3KCL launched his S-9 balloon 4 days ago (2 standard party-balloons, hydrogen-filled) with modified QRP Labs Ultimate3S QRSS/WSPR transmitter onboard.

We are using WSPR messages for tracking - one normal WSPR message and one with a special data protocol to provide altitude, speed, Maidenhead 5/6th characters, battery voltage, temperature and GPS/satellite status. The transmitter has about 16mW power output, on 30m band. It is sending CW and JT9 as well. Altitude is a little over 10,000m. So far it has traveled in several loops around Greenland and the North Atlantic. Currently it is near the Faroe islands. See live tracking at QRP Labs website http://qrp-labs.com/ultimate3/ve3kcl-balloons/ve3kcl-s9.html

G-landers, don't get too excited that it appears to be heading your way - the wind prediction shows it likely to head back West almost as far as Newfoundland, before turning back East towards Spain!

73 Hans G0UPL

http://qrp-labs.com

http://hanssummers.com

Some Thoughts on Noise and Receiver RF amplifiers from Scotland (and listening to sun noise on 2 meters!)

Bill,

Just listened to the latest SolderSmoke podcast where you asked why is it that an RF amplifier may be required on the higher bands but not on 40m and 80m for example.

At high frequencies the atmospheric and ionospheric noise levels are lower, so if noise figure of the receiver is reduced it will improve the signal to noise ratio you get from the receiver.  Adding gain -after- the mixer will not improve the noise figure of the receiver as it will be limited by the noise figure of the mixer. You need an RF amplifier which will itself have a lower noise figure than a mixer (certainly a passive mixer), to lower the total noise figure of the receiver to take advantage of the lower effective antenna noise temperature at higher frequencies.

This becomes very important at VHF and above, where antenna noise levels are much lower than at HF.

So, it isn't so much the overall gain of the receiver that is important with weak signal work, but the overall receiver noise figure which is determined to the largest degree by the first stage of the receiver.

There are spreadsheets available that will easily calculate the noise figure of cascaded receiver stages knowing the individual stage gains and noise figures.

One also has to be careful with the gain distribution throughout a receiver, if you have too much gain early on in an effort to improve the noise figure overall, you may overload the subsequent stages producing IMD with multiple strong signals. So there is a compromise to be met between noise figure and strong signal performance.

Going back to VHF and above if you have an antenna fed by coax with some appreciable loss then improving the receiver RF stage noise figure is not the best way to go because you are amplifying the signal after the loss the of the coax. What you need to do in those circumstances is to use a low noise masthead RF preamplifier which will give you gain and establish the noise figure of the receiver before the loss of the coax. Again there are spreadsheets to help with these calculations.

At VHF where an antenna is pointed at the horizon, the antenna sees the noise from the ground on the noise from the sky. As we elevate an antenna for EME or satellite working, then the effect of the ground noise should reduce (there will always be some due to side lobes) and then the receiver can benefit from even lower noise figure as the effective antenna noise temperature is now mostly determined by sky noise which at UHF is much lower than ground noise.

These last two days I have been able to see and hear the sun noise on my 2m receiver as the sun  set on my single 10 element yagi pointed at the horizon. Using WSJT's noise level scale I could see it  measure 12dB noise level and then once the sun set it dropped back to about 3dB noise indicated, most of that being local QRN from an antenna  sidelobe from my neighbour's house and his electronic devices which put out quite a bit of wideband noise on the band. (about 8dB above the lowest background level  I can normally detect).

To summarise, at LF where noise is high you don't gain anything by having a low noise figure receiver, and you actually lose out if you have too much gain early on as it will degrade strong signal handling.

At HF as manmade, atmospheric and galactic noise levels are lower, you can benefit from lower receiver noise figure and the way to lower your noise figure is to use lower noise amplifiers in the early stages of the receiver. Adding gain in later stages does not reduce the noise figure overall as the noise figure is largely determined by the first stage or stages.

At VHF using even lower noise figure devices in the RF stage will improve signal to noise.

Here is a practical test you can carry out. Switch between a dummy load and your antenna. If the background noise level increases when you switch to the antenna, then your receiver is sensitive enough, lower noise figure in the receiver isn't going to help.  If it doesn't increase then you have scope for improving the sensitivity of the receiver by reducing the noise figure of the receiver as you are no longer limited by antenna noise. 

Incidentally it is good to have a preamplifier that can be switched in an out of circuit so that you can reduce the noise figure when conditions allow ( low noise atmospheric noise levels for example), but switch it out if noise levels are high and signals are strong so that receiver overload and IMD don't occur. You can do something similar with an input attenuator to reduce strong signals where necessary.

I don't have a link here to the graph of manmade, atmospheric and cosmic noise levels versus frequency, but once you see one it becomes obvious why low noise figure receivers are not required at LF and MF generally.

73 from David GM4JJJ

Bill,

I found the article with graph of noise v frequency at last, in Ham Radio Magazine 1975!

A good read and as valid today as then.

http://www.r-390a.net/Receiver-Specifications-Explaned.pdf

I don't have a link here to the graph of manmade, atmospheric and cosmic noise levels versus frequency, but once you see one it becomes obvious why low noise figure receivers are not required at LF and MF generally.

73 from David GM4JJJ

Soldersmoke Podcast #186 Is Available -- April 1 Rap Up, Pi Talk from Pete, Collins and Raspberries, Bill's Analog RX, Visits and Hamfests, MAILBAG

SolderSmoke podcast #186 is available:

http://soldersmoke.com/soldersmoke186.mp3

-- April 1 WireWrapRap Rap-up.  Feedback from participants.

-- Bench Reports:

   - Pete talks about his Raspberry Pi SDR DSP rig.  

   - Bill talks about on his Mate for the Mighty Midget Receiver and his R2 Frankenstein.

-- A story from Pete's youth: Cruising the "Miracle Mile" with a Heathkit "Ten-er."

-- Why do we need more RF amplification (in receivers) on 20 than on 40?

-- Have you ever tuned the BFO freq in a superhet by the "sound of the noise?"  

-- A visit to Washington by Jonathan W0OX and family.

-- Bill goes to Winterfest Hamfest with Armand WA1UQO

-- Pete on the importance of balance (in life).

-- Great interviews on QSO Today: Peter Parker, Grayson Evans, and Ashhar Farhan.

-- MAILBAG:

- Paul Darlington M0XPD has a new book about life, travel, and the Dayton Hamvention.

- Michael AA1TJ QRV with a tuning fork at its 2,000th harmonic.

- Jonathan M0JGH living dangerously with homebrew QRP in Italy.

- Ben KC9DLM JoO with MMM

- Stefan DL1DF needs 3.579 MHz rock "with mojo." We have it for you OM.

The music for SolderSmoke 186 was written and performed (the bass lines) by Pete's son Tim.  Thanks Tim!

Pete also suggested that we have some rap lyrics for this music, so renaissance man that he is,  he composed some words. We are still looking for a performer.  

Yo we solder no more – its wire wrap and cables

The cables connect to the small  black box

hold on to your pants and pull up your socks

A cable goes here and a cable goes there

Turn on the switch and its Shazam all software

 

From Vietnam to Washington DC -- Jonathan-san KC7FYS W0XO 7J1AWL XV2OC Stops By With His AT3b

I first saw that QRP Altoid-tin ATS-3b rig  around 8 years ago in pictures that Jonathan-san sent from a beach in Vietnam.  He and his family were there on vacation from Japan.  (Included was a memorable picture of his young son in an NVA helmet.) During this time period Jonathan also tried (unsuccessfully, I'm afraid) to teach me how to properly pronounce the name of that famous electronics market in Japan.  

Jonathan and his family were in Washington yesterday and we got together for lunch.   It was great to finally meet them.  And to see that well-travelled ATS-3b.

Jonathan is a big fan of the ATS-3b, and for good reason.  A very neat rig.

Plug in filters for the ATS-3b.