19 September 2014

The 40m BPF to improve the reception in MM/HP contesting


when You are contesting in MM/HP category then You know very well that filtering is most important on each band...

In our case the 40m band was the biggest problem mainly because of breakthru from 160m band.

Even although the band decoder/PA lines used the proper TX BPFs for each band the reception on the 40m band CW was nightmare when 160m band operator operated the RUN station.

I started to modifying the lowband setup step by step... At first I installed the front-end savers into all external RX inputs of transceivers and decided to build good more-order BPF for 40m band receiving path.

I prefer the rugged and well shielded box for this filter to avoid blow-by the signal so decided for Hammond alloy box. It is really expensive but "You have what You paid for..."

As I had not enough time (as always I started to solve this issue just 1-2 weeks before the CQ WW) so I did not spent time with PC analysis, PCB layout etc. Simply I found and used the good design from W3LPL (mni TKS guys) and though "Network analyzer will say more..."

If You are going to build Your own filters also then do not use unknown or low-end components for the filter. High quality NP0/Silver Mica capacitors and Amidon cores (Hi-Q) as same as high quality connectors (PTFE) is the goal.

After assembling the filter on the breadboard I realized that the PCB is installed too high in the box and the cover is just 1mm above the components itself. In order to avoid the unwanted influencing of the filter and it's final performance by the closed cover I decided to reinstalling it and drowning the PCB as low as possible in the alloy box. It was not easy as the connectors did not fitted to PCB as at the beggining...

Well finally I solved all issues and even I found the way how to properly grounding the components together with alloy box and connectors with minimum junction points.

The first shot on the Network Analyzer (thanks to Mr. Hewllet and Mr. Packard) was not so satisfying...

I was not happy with the ripple as same as the insertion loss was a bit higher then I expected.( Network Analyzer has been actually calibrated and used measuring coaxial cables has been compensated properly)

Although I kept all values exactly as stated in W3LPL cookbook (even the coils has been tuned on the RLC-meter for their proper values)the slight modification has been needed.

After short alignment the BPF seemed better. I had to remove some wire (1wdg) and modify the coupling capacitors between the LC stages to get better response without ripples.

Also the insertion loss went down for 0.5dB (although it is still not satisfying for me and it will need some time in lab) and I decided to keep it like that for the coming contest.

Final result after tweaking and then closing the box is not so bad. The main goal the stopband on 160m band looks like over -100dB and the insertion loss on 40m is slightly over -1.5dB.

73 - Petr, OK1RP

11 September 2014

Noise cancelling headphones - part II.


in preview part I did not mentioned anything about the "second" way of the noise cancellation which I named in my article "the passive noise cancelling" method.

As I realized that it is a bit confusing so I am going to try explain what I mean by these ways of noise cancellation...

Active noise cancellation

As I already mentioned more detailed in the first part - the noise cancellation (more or less known as ANC) takes an active approach to blocking-out an external noise. There are one or more microphones built into the headsets to detect external noise. Using the electronic signal processing an "anti-noise signal" is then generated to cancel-out the external noise.

        Bose QC-15        
In fact it is leaving only the desired outside disturbing noise that is reaching Your ears in the room. With a pair of good ANC headset You should hear your intended radio signals without any background noise.

Passive noise cancellation

The passive noise cancellation does not make use of any electronics to blocking-out surrounding noise. In fact it is using the different of construction materials and an ergonomic design to blocking-out as much background noise as possible coming to the ear canal. With respect to this fact it is better to talk about "noise isolation" instead of cancellation job...
For big headsets (mostly known as over-ear) it is commonly done by soft and thick memory foam earcups padding that fits snuggly over your ears. The fact that it fit "airtight" inside your ears keeps the noise out.
For in-ear earphones which are probably not used for ham radio applications so often the eartips are ergonomically customized to fit securely in the ear canal which effectively forms a sealing chamber within the ear canal and blocks out external noise significantly.
So in summary...
Noise isolation or passive noise cancellation or noise reduction

is provided when headphones totally cover the outside of the ear or ear buds can be used that fit snugly into the ear canal thereby preventing external background noise, buzzing or sound reaching the listener in the first place. Passive noise reduction (better we should call it noise isolation whenever) is mostly used to cancel-out unwanted high frequency sound which is difficult to effectively removing using an Active Noise Cancelling (ANC) system. This is the reason why better headsets are using both - good noise isolation as same as the ANC gadget inside...

 Goldring NS-1000

For example in my small radio room I measured over 78dB of background noise when all power amplifiers, power sources, computers and other fan's equiped stuffs running and it really make sense for weak signals pulling out. Just to compare > when all is down the ambient noise is measured around 30dB in the room. So this is my personal reason of looking for good quality and effective ANC headset.

Another headphones test by Mark, PA5MW can be found here.
Hope it helps a bit.
73 - Petr, OK1RP

03 September 2014

The best AGC setting for weakest lowbands sigs pickup on Elecraft K3


as I am lowbands enthusiast and the Elecraft K3 transceiver owner also... I am interresting in any kind tools, h/w as same as K3 setting how to pick up the very weak CW signals on the lowbands (160/80/60/40m).

I started to play with wide variety of AGC system setting in my K3 and I am currious which kind of setting is used on K3 by other users...

The links and sources which I already visited (documents for study/research):


In fact I used for long time the AGC off in cases of pulling weakest sigs out of the noise but specially in pile-up it was really danger when the strong sigs attack my ears.

For that reason I would like to use all of opportunities of AGC system in K3 with proper setting. So I will be happy for any kind of settings hints and experiences for CW weak sigs handling.

I am trying to play with the AGC system setting in order to optimize to my needs (weakest CW sigs on lowbands). I am sure that it will be different from other users also because of my local background noise/noise floor environment, disturbation and other noise sources...

My original setting was for years as follows:

AFV TIM: 1000 / AGC DCY: NOR / AGC HLD: 0.00 / AGC PLS: NOR / AGC SLP: 14 / AGC THR: 3 / AGC F/S: 120/20

... but it sounded so noisy and I commonly turned AGC off in order to get quieter RX for weak sigs. Of course that I was attacked by strong sigs in pile-ups or contests and I was punished when AGC was off.

After some discussion on Elecraft reflector I got few recommendations from which I finally decided to try this config:

AFV TIM: 1000 / AGC DCY: SOFT / AGC HLD: 0.20 / AGC PLS: NOR / AGC SLP: 000 / AGC THR: 8 / AGC F/S: 200/20

... which was recommended by several users for weak CW signals reception. (many thanks to Merv, K9FD/KH6)

I found very quickly that the receiver appeared a bit noisy so I added N1EU pink noise roll-off on RX EQ.

I used the left side red column settings:

http://n1eu.com/K3/K3_notes.htm (many thanks to Adrian, VK4TUX)

It helped I guess but I realized that the behavior of AGC in my K3 with this setting is in general not what I am looking for and I do not like it so much. The improvement is that when there is no signal on frequency then this setting of AGC sounds more quiet than AGC off for now! 
Unfortunately I do not like the "slow pumping" of AGC which is pulling down the receiver gain some time...

So I am looking for another settings or ideas and I am going to make more research.

73 - Petr, OK1RP