A good old active filter...

Nowdays everything is digital. I hear old mates talking on 40 meters complaining of the voice of their brand new HF radios. Digital … as they say... never sounds as good as those old rigs with tubes inside.

I have been using an FT-450AT for a while. Why FT-450? When I moved to Hungary it was the cheapest piece from a trusted seller. It has everything I need, specially narrow CW filters. Almost a decade ago I had an IC-7200 I really loved. FT-450 is very similar in it's category. Of course just similar, but not as good. Okay, I am not complaining, it does it's job, and for a casual ham like me it is more than enough. It is not a contest “king of the field rig”, but if one is able to understand it's features this radio can be a good friend.

This post is not about FT-450, there is something else. 

Few weeks ago I had a deal with a local ham. Finally I received an old DAIWA AF606K filter. Originally I wanted an external speaker, but I was curious, and it has a big speaker inside, so why not to give it a try?

It is built like a tank. Reminds me pretty much the good old 80's. Basically it is an active filter for SSB and CW mode. There is a PLL function is, but I would not use that in real life.

It has four knobs on the front. Notch, PLL lock frequency, band pass for CW and mode. Input is low impedance, so speaker can be connected straight. When turned off, it behaves like a speaker, turning it on the filter starts working.

I have almost broken it at the first time. Pwr supply connector is reversed... inside is negative and outside is positive. Ghrrr... I changed it so quickly therefore it fits to my domestic standard. After trying it I noticed a strong feedback noise in SSB. I checked the whole station, and found everything fine. The weakest chain was the filter. Also the speaker had terrible voice, while using my headphone it was perfect.

After several minutes I found the problem. Few ferrite filters inside, and proper ground connection between the front panel and the PCB made it OK.

Result is amazing. I really like listening CW QSO parties, and also taking part... The filter saved me dozens of pain killers. I turn on narrow CW filter on the 450, and turn on the filter, play with the notch, and no noise, no static, just the pure signal. No matters how weak the signal is, it makes it easy to copy, easy do dig out from the noise and above all CW reception has become relaxing.

If you find one on a hamfest, or even ebay, do not hesitate to buy!

I will make a short video clip later to show what it does... and picture as well of course.

Another transformer...

Size matters. Funny as it is, in QRP world the smaller the better;) 
I've given my QRP transformer to one of my friend, therefore the time has come to build a new one. 
I don't want to carry patch cables, coax connectors and so on, an UHF male connector is the perfect idea to connect straight to the tuner or the radio. 

I've dropped it to the floor right after finishing it as the proof of the pudding... As I wanted it is military standard "IP howmuchever standard":). No damage, mechanically quality-tested.

Nothing more to write about it, all you need is in the pics. 


The transformer is the traditional trifilar one, 8 turns on a ferrite (god knows what type, it is from the local DIY shop, but I have tested with analyser and found it perfect from 3 to 30MHz), inside of the box is full hot glue. 
Hot glue is my favourite... it makes everything waterproof, shockproof ant so on. 
The only disadvantage is the "no way back" effect:) Once you have filled the box with this plastic stuff you will never take it apart again... 
No chance for mistakes. In the HF range it has no effect on the system.

Ground has a banana socket on the side, while 1:4 and 1:9  output has their dedicated connectors (two red gadgets on the right side)
Few words about the UHF male connector... 
There is a piece of PCB with a whole inside. The connector is soldered to the PCB. It is the easiest way...

Miniature tuner for end fed half wave antenna

I said good bye to my military backpack. I used it too hard, weight was to much for it, and quality was not good enough. In most cases I take many things with me up to the mountains. Small survival pack can grow so big quickly when a tuner, few more battery pack, or few extra meters of wire (and so on...) should be carried. 

I decided to put a lightweight and small setup together. The old Ft-817 can not be lighter, also LI-PO batteries are the lightest options, but my tuner is not the smallest no matter how good it is working. My favourite setup is a fishing pole and tuner combo antenna. I wanted to create something smaller than that. 

One of my friends Gabor HA7MAC told me about the idea of using a transformer with a cap at the coax side with half wave radiating element. Gabor is a top bloke and also fanatic QRPer. If he says something I will listen, because there is always something to learn... The original idea is from PD7MAA. The source of the circuit can be found here: http://pa-11019.blogspot.hu/2012/04/149-transformer-for-endfed-antennas-35.html 

I had some FT-243-like toroids and started the test on a rainy afternoon. 

Finally I decided to use a smaller core, but it is still well enough for QRP usage.

This is a recycle project, only used parts are in the box. The cap is changed to a vinyl variable one, and a small tuning aid with a led is also built in. You can find the description of it below. It is switchable of course not to eat too much from the QRP power.

 Size matters... as you can see it is really small. Smaller than a cigarette box.

Banana plugs are used as connectors for CP and the radiating element. 

The switch on the right side is to disconnect the tuning indicator from the line. 

I prefer using counterpoise even with a single wire antenna. It makes the system stable and easy to tune. There is a set of radial wires for my vertical setup with banana plugs at the wires' ends, therefore I didn't have to make CP wire kit for this project.

Using is easy. Just connect the half wave wire to the ant banana socket and twist the cap for best SWR on the radio, or the brightest light on led.  

As you can see, inside is not over-sophisticated. The white stuff on the core is plumber tape. Hot glue can help to keep things on their place. Germanium diodes are made in Hungary in the mid of 70's, variable cap is a cheap Chinese one from a small broadcast receiver.

The transformer is a bit tricky. PD7MAA describes every details of it. In nutshell, there are two times seven turn, plus two more with twisted wires at the feed. The end goes to GND, while the twisted to the input. 

One has to be careful not to touch the output of the transformer while transmitting! It can burn your finger even at QRP level. 

On air tests? I need some time to test, compare and I will share my experiences later. My plan is to compare half wave end fed, norcal-like doublet with speaker cable, norcal-like doublet with professional symmetric feedline, doublet with 1 to 4 transformer 5m vertical with my L-match tuner, with tuner+unun and one of my mate's ZM-2 tuner. The goal is to find the smallest and the most effective antenna for QRP prtable use.

I will use swr meter, analyser, and field strength meter with live on air tests of course. 

Are you curious? Come back later! :)

Update:

I have tested many antennas comparing tuners, transformers etc... 
This one works. It just does the job. What you need to take care is the proper length of the counterpoise, the antenna height and the sloping angle. Honestly a quarter wave length vertical, or random wire antenna of course with radials performs just as well as the half wave one, with difference hardly noticeable. An "L" match tuner is a bit bulkier of course, but practically it is easier to work with it when operating qrp portable.
The half wave antenna with this tiny tuning unit is very useful, when one has a favourite place with fairly the same conditions all the time, same height, angle and so on. In this case big tuners can't beat the mini half wave coupler. 
In case of a weekend house or camp house I would prefer building a big matching box with large coils made of silver coated wire to reduce losses.
Anyway, It was good experience and great fun playing with it. I am sure I will take it with me to places where high watchtowers or trees are surely waiting for me...

Tuning aid for QRP field gear

FT-817 is an ultimate QRP field radio. There are plenty of new field rigs, but the old 817 is still one of the best choice. Of course it has few minor bugs as all the other fellas have. Its internal SWR meter is one of them. It is more like an SWR indicator instead of SWR meter. The bulit in bridge is not so accurate, therefore it is not possible to tell the difference between SWR 1.1 and 1.8 simply watching bars on the screen. In both cases it says no bars at all...
The tuner I built last time has an internal tuning indicator. It is so easy. Two ge diodes, a cap, and a small meter. There is also a led for dark environment. Sensitivity can be set by twisting a 10k pot. This tuner works really good. I've tested it with a 5m long vertical and few CPs against a doublet with ZM-2 tuner. 
Mine was significantly better. The station was able to hear me loud and clear enough for reliable communication, while doublet and ZM-2 was weak, and signals were hard to copy. There were stations unable to copy the other setup, while giving fine reports to mine. 
While trying the doublet mounted next to my rig I noticed the needle was dancing on my tuner's meter. I tried the led indicator and I was able to see the light and observe the changes of the signals on that as well. I decided to build a stand alone field strength indicator for QRP field days. 
Here it is:

The circuit is easy. It looks exactly the same as the one you can find here https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiRPO1C5HFqyEIOg818nPQvyP6Wsjo2fKdbagdgny89TvIJCAZHERdmFGFoI-_flwrRaVIkcYgMJuS_JsAdb0YuYkkrFyvFnqz29Yy3e_sEIz8evcPfxIrg0XbKKOzpxh3cniK1rRo639o/s1600/tuning+aid.GIF

 Thanks to PD7MAA!

There are two banana plugs for the antenna and GND cables. BNC for my small telescopic whip is mounted on the front. This way it stands on the desk if needed. The small patch cable with the croc at the end goes right to the gnd terminal of the FT-817. Sensitivity can be set just by twisting the pot on the middle. Few watts are enough to light the led up from few feet away from the antenna. 
After tuning the antenna to 'no bars' on the radio, just set the pot to low light on the led. Tune it until the led will give the brightest light.

Price is so low... every parts are recycled, except the plastic box. (aprox 30 cent:))

Update: 
My friends asked me to lend it to them for a test, therefore I made some stickers to the face of the box. Does not look professional, but helps to find out what is for what purpose on this over-complicated front end:)
Also I made a pic of the inside. As you can see it is not a sort of rocket science:)

QRP antenna tuner

I have sold my Z-817 tuner. I have been missing it since, but that time it seemed to be a good idea... Okay, let's forget the mistake and do something instead!

I needed a tuner. For all kind of wires, whips, dipoles, only for QRP portable use.
Mainly I use my FT-817. It has built in SWR indicator. Yes, it is only an indicator. When it says SWR is 1:1, indeed it will be somewhere between 1:1 and 1:8, or higher, therefore power indicator is needed.

I tried several cheap plastic switches for inductance, but they turned to be low quality with several Ohm resistance. The only way for an "L" network is a switched system. Basically it is the same as the LDG autotuner. Of course it is not auto. I use switches instead of relays. 

Coils start from 0.25uH up to 16uH, hence all together I have 32uH if needed. It seems to be enough in most cases. 
Cap is a plastic one from a pocket AM receiver. Unfortunately it does not start from 0!!! The small meter is from an old handheld CB. It was not working due to some mechanical sock, but after spending few minutes fixing it with a small screwdriver it came alive again.
Power indication is easy, just two old germanium diode via a 10pF capacitor, and a 10k trimmer pot. Input and output connectors are UHF ones, plus there is a gnd banana plug for counterpoise. 

It works fine, a bit better than the good LDG... Okay, it is bot as easy to tune, but after the third try one can start thinking in binary mode:)

Here are the pictures. There is no schematic. Internet is full of these "L" network schematics, so just call google image search with the keyword "switched L network" and the help is on the way:)

(price is aprox. 13dollars... or below)

Kinder unun

There are few things you can not buy in USA. One of these is Kinder-egg. I don't really think it causes more fatal accident than reckless gun handling... anyway, in Australia or Europe it is easy to buy the dangerous Kinder-egg. 

One day one of my best friend started to think about building a portable end-fed QRP antenna for portable setup.

He found this link: http://pa-11019.blogspot.hu/2012/04/149-transformer-for-endfed-antennas-35.html

Easy to build, works fine and so cheap. Okay, but where to find a perfect enclosure? Here we go! Kinder!

If you live outside USA, don't hesitate to give it a try!