12 decembrie 2014

Home made IF Filter

Today I started wondering what should I do with some quartz cristal that I have around...
A IF filter was my first thought and I started to fool around with them.
First, I cut a small piece of PCB and prepared for "dead-bug" soldering style.
I prepared also two small piece of RG58U to connect the filter to a Marconi IFR analyzer.
In my box I had two type of cristals.
One type is a 4 MHz and the second one is a 38.9 MHz, both of them HC-49U format.
First I started with the 4 MHz ones but I didn't noticed a nice shape on the analyzer so I quicly moved around to 38.9 ones.
These are overtone cristals so I watched to fundamental frequency which had to be around 12.6 MHz.
And it was!

I don't want to bother you with math stuff. Instead, I will put the self-explanatory pictures.

The two SMD resistors are 470 Ohms and the small SMD capacitors are 1nF.

Here it is the filter on the tests. After tests, it can be put on a smaller and nicer board. I didn't had capacitors, I will play with them monday, HI.
 There are 9 cristals. At less than 1 USD, I believe is a good alternative!
Indeed, one had to choose from a big bunch, but I had an already opened bag of cristals with around 25 pcs. I observed on the analyzer that there was two type of shape for that bunch.

The insertion loss is around -4db wich is not bad at all!
 The center frequency was set at 12.96400 MHz. This might be somehow unusual for elder hams but with modern DSS it's easy to set the IF to this value.

 -22db attenuation at +1.5 kHz

 -27 db attenuation at - 1.5 kHz

 It has a passband of around 1.8 kHz at -15 db. Maybe I will send it to some experimenter who want to play with because I am very curious about how it sound in the real HF traffic!

Other pictures:

06 octombrie 2014


Or, "Why I Refuse to Let Technology Control Me"...

25 septembrie 2014

LiIon charger with LM317 and Cutoff circuit - Part I

Very often I need to charge one or two series LiIon cell for my experiments.
I do have a sophisticated battery charger and analyzer but I don't want to use it every time.
I need something simple yet safe.
There fore I came to a nice shematics here.

It is a very simple schematics using just one LM317 and two NPN transistors.
I made some modifications.
The most important is R7 which is 6 Ohm for a 210 mA current.

Despite the urban myths, the Li based batteries are very safe at charging if you respect two rules:
1. No more than 4.2 V per cell
2. No more than 1.5 C (thats 1.5 x Nominal capacity in A) charging current.

The main advantage is that at the end of charging, when the battery has the desired voltage - in our case, 4.2 V/Cell, the charging current drops to zero. The bonus is that the LED lights during the charging phase.

Yes, I know, there is CAD but I like the old fashion way to make a PCB. By hand with a fine marker...

Here are some pictures....

I plan to put this with a 12V/2A SMPS into a small box.

09 septembrie 2014

Kantronics KAM Plus

I found on my junk box a Kantronics Kam Plus modem. It stayed there about 2 years untill I found (yes, in my other junkbox) a 25 to 9 pin COM adapter...
I connected to a terminal and nothing happened, just garbage on my screen so I search on internet  and came to this reset procedure:

1)  Open the case
2)  With modem power off, install Reset Jumper, K6 (near the largest IC), on the two posts.  ( no need to touch the battery).
3)  Using terminal program (WinPack or others) with baud rate set to 1200, power on the modem.
Modem should respond with :

....RAM OK

4) Power off the modem; return jumper K6 to one pin only.

5)  Power up the modem;  Watch for: 
PRESS (*) TO SET BAUD RATE*   (You must do this within 2 seconds).


You should now be in NEW USER mode. 

6)   Check your call sign by typing    MYCALL

8)  To change from NEWUSER mode to TERMINAL mode type    INTERFACE  TERMINAL

cmd:in terminal
in terminal

9)  To change from 1200 baud (because Airmail doesn't go that slow)  type in ABAUD  0 
cmd:abaud 0
abaud 0
ABAUD was 1200

Now, everything is ok , awaiting a proper radio and setup to test. Unfortunately, only CW and RTTY seems to be appropiate in these days since PACTOR, AMTOR and other modes like that ceased in favor of PSK.
Maybe this nice modem will find it's place as a APRS digipeater, who knows!

29 august 2014

My Dream "GO-BOX" for emergency communications. Or just for fun!

Well, I sibscribed recently to a FB group dedicated to emergency communications. Its a very nice group.
I do not believe in the FB because it's like the sand. You write something or find something but soon it's hard to find it again.
I like very much to have the possibility to go somewhere and try to make some QSO's. I am not a contester and I appreciate a nice chat with a fellow ham from here or anywhere. Therefore, I realise i really need a "GO-BOX" or a "GO-KIT" able to work all mode, all frequencies from HF to UHF.
Also the kit will be good for RVSU which is a network of hams involved in emergency communications for various NGO's here.
I will tell you my secret: My GO-BOX is on wheels!
It's a Nissan X-Trail "doped" with a lot of ham-stuff.

The main radio is a ICOM IC-7000 mounted in the trunk and the front panel remote. I finally made the permanent setup; the radio is under the trunk hood, bolted with the optional DC filter (OPC-639) and on the HF side I put a choke Balun  to reduce the common mode currents from the Codan antenna (or any  othe HF antenna) because the IC-7000 remote head is very sensitive to that issue.

The remote head is under the radio; i put it in place with the help of some industrial 3M velcro. In the left side is a small loudspeaker connected to the remote head. I use that velcro also for phones, portable radios etc...

The main attractions is the Codan 9350 auto-tuning antenna. Bulky but with outstanding performance, it's definetly a magnet for everyone's eyes, in march or in parking lot!

I wrote in other post about the custom mount for this antenna and about the connection with ICOM IC-7000 radio.

What I did lately was to put all the important wires in a protection harness.

 The main 12V DC is in harness, the RG58 and the command cable for the ATU antenna is in the harness also. Was a little tricky but the final result is amazing!

For VHF and UHF I use quarter wave antennas. I found that if I put a quarter wave on VHF, the same antenna is resonant also in UHF! A MMANA-GAL simulation showed that the UHF angles are somehow elevated but still a +2db at 0-15 deg. over the horizont so the antenna can be used well.

I preffer NMO (New Motorola Mount) for my mobile antennas. This is a special designed mount to accomodate proffessional antennas ant to whitstand to all the special conditions on a  mobile setup in full run. Do not ignore that! And also, keep in mind that a fixed mount is BETTER than any magnetic mount.

Here it is a NMO mount, VHF quarter wave antenna.

Now, for really serious things like emergency comms., I have a little toolbox with a 35 Ah SLA battery.
I was looking for a good battery eliminator but the price was too high and had to buy it from overseas! Hey, I think a little here and I know how to use a solder iron. Or solder station. Or something like that, you figure out...

So I made a very very simple "battery eliminator" or "separator", whatever, from a Schottky power diode. It was a bulky one, I don't know at what current is rated but did'nt burned at 14-16 Amps so must be better than that. In the little Hammond box I put a little 5 LED voltmeter to quick view the main battery status.
The later addition was a little digital voltmeter on a "Y" cable to view the voltage. Both of them are usefull.
The battery have two fuses, one for plus and one for minus.
Some hams think that if they put a single fuse, on the plus side, is enough!
Well, what if you make a shortcircuit between minus cable and the "plus" pole?

That toolbox cand accomodate the ICOM IC-7000 or anything else. In this setup made for Ciucas Trail Running (a 100 km mountain marathon) I have two Motorola mobile radios.

The lower is a GM360 VHF radio to talk to Salvamont (Mountain Rescue) teams and the upper is a DM3600 to use it with the Radioamateurs in the RVSU network (Radioamateurs for Emergency
In order to be able to use a single antenna, a diplexer is used. Is a Diamond 2000 with modified RF cables. The original ones was too bulky and used PL and N connectors.
A lot of hams use amateur equipments for frequencies above the 146 or 148 MHz. They tend to ignore that out of the regular amateur bands, the radios are very ineffective!
I measured a lot of radios and they seems to loose power after 150 MHz and become very insensitive over 155 MHz. That's how they are made...  So, in a emergency network I found a little stupid to use deaf and mute radios! Therefore, I will go with proffessional radios for that particular case and the choice is Motorola!

A completion to my HF setup is a AH4 ATU with a collection of wires. I use two lenghts, 8,5 m and 4 m as they are not half-wave, as reccomended by ICOM to use them with AH-4.
The trick here is that I made two lenght of control cable and RF cable (tied together) so I can use 5m or 10m from radio to AH4.
The AH4 can be used for tuning a horizontal antenna (dipole) or a vertical one (erected on a fishpole stick) using 2 equal wires or 4 counterpoises with a vertical radiator. That's why there are 5 cables at the same lenght...

Well, this is my GO-BOX!

4 wheels and radios!

For final, here it is with a strange VHF antenna on the rooftop!

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