Thursday, 30 October 2014


This device from Google brings internet video to your TV; it gives some brains to a dumb TV with an HDMI port. 
For  35 euro  I purchased this gadget ("Mediamarkt") and I am quite happy with it. I can send wireless internet to my Samsung TV now. Most of the times I use it to watch YouTube or websites via the Google’s Chrome browser (using the tab casting feature). 
You must have access to a wifi network. It is not possible to connect the Chromecast dongle to a LAN-connector.

It is funny that you can cast video via your smartphone as well when you have the Chromecast app installed. The development of lots of apps that can work with Chromecast is on going.
I think it is a smart, inexpensive and usefull gadget.

Chromecast dongle

                         YouTube in action on my TV showing a homemade BITX20A

Friday, 24 October 2014

13 cm radiolink budget analysis

I discovered that the video signals from my 2 Watt 13 cm transmitter reach the PI6ZTM repeater, normally producing an acceptable picture.

A link budget analysis can be made for this signal path:

Transmitter side (36.9 dB)

Transmit power: + 33 dBm
Note: Pdbm = 10.log (1000.2W)= 33.01

Cable losses: -4.1 dB
Note: consists of
- RG/6U; 34 dB/100m => 3.4 dB (for 10 m)
- Mismatch due to use of 75 ohm coaxcable: swr = 75 ohm/50 ohm = 1.5 => additional losses: 0.2 dB
- Connectorlosses 0.5 dB

Antenna Gain: 8 dBi
Note: biquad homemade

Receiver at PI6ZTM repeater site (87 dB)

Antenna Gain: 10 dBi
Note: estimation waveguide slotted antenna

Cable/connector losses: - 3 dB
Note: rough estimation

Sensitivity threshold receiver: -80 dBm 
Note: rough estimation

Propagation (-116.1 dB)

Propagation loss: -116.1 dB
Note: Friis formula: Lp=92.45 + 20.log(F) + 20.log(D)
F in GHz and D in km makes:
Lp=92.45 + 20.log2.4 + 20.log6.3 = -116.1

Now we can calculate the link margin:

(Transmitter) + (Receiver) - (Propagation) = 36.9 + 87 - 116.1 = 7.8 dB

This value is within the range of 6...10 dB which is required to obtain a good radio link ('rule of thumb').

Note: The receiver sensitivity, cable/connector losses and antenna gain at the repeater site are estimates. The receiver (in fact converter) is mounted a few meters from the antenna hence cable losses are not that high.

Sunday, 19 October 2014

13 cm experiment

It turned out that you do not need to make a complicated circuitboard with stripline technology or other hi-fancy stuff to generate a 13 cm RF signal.

Yesterday I was able to transmit a video signal in the 13 cm band (on 2335 and 2365 MHz) to the video repeater PI6ZTM with a modest setup.

I made a small videotransmitter which provides about 10 mW (I guess) using a Z-Comm VCO  V804ME14.

Z-comm PLL VCO V804ME14

Th V804ME14 is followed by an MSA-0886 for some gain. Of course 10 mW is not sufficient to bridge a couple of kilometers. A PA was required. These days it is not really smart anymore to homebrew an RF amplifier at this high frequency yourself. A variety of WiFi boosters supplying 2..5 Watts are available. I bought a 2 Watt "Wifi 802.11b/g Wireless Broadband Amplifier Router 2.4Ghz Power Signal Booster" for $25 on ebay. 

                                          2 Watt WiFi broadband amplifier for 2.4 GHz

I received some comments from experienced ATV ham amateurs (PE1ODJ and PE1DWA); they informed me that the picture shown on the repeater channel was not too bad. After I directed my small biquad antenna better to PI6ZTM sometimes the picture was almost free of noise and glitches (but not always :-)  ).

                                      Simple videotransmitter setup for 13 cm 
(..if you cannot fix it with ducttape you are not using enough ducttape... :-) )

                             Dimensions biquad antenna for 13 cm

Friday, 10 October 2014

Programming cable for UV-5R

For programming the UV-5R in channel mode you better use a PC. The Baofeng UV-5R handheld transceiver uses an RS232 interface to communicate with a PC. The circuit of the programming cable presented here contains a 3V3 level converter. A 2.5 mm loudspeaker plug and a 3.5 mm microphone plug connect the radio with the PC. In the software select the proper COM port.

The software to program the variables (frequency, shift, channel name...) can be found here:

Saturday, 4 October 2014

External antenna for UV-5R

It is easy to extend the transmit/receive range of a handheld transceiver. Simply connect a better, external antenna.
I made a simple SMB-BNC joint to connect an external antenna to my UV-5R.

With a 2m  HB9CV antenna it is quite easy to reach the repeater stations.
The repeater PI3UTR in IJsselstein came into range for me now on 145.575 MHz (shift 0.6 MHz, 77 Hz TX subtone) and it is rather easy to make FM QSOs.

The TX antenna of the repeater is located at an altitude of 220m and the receive antenna even higher (300 m). This repeater covers at least half of The Netherlands.

HB9CV for 145 MHz

                                      Gerbrandytoren Lopik, with PI3UTR repeater

Note: On the PI2NOS repeater (430.125 MHz) I was informed by Rob, PA3CNT that I should select 'WIDEBAND' in menu item 5 (W/N) of the porto to enlarge the modulationdepth of the transmitted signal. So I did, and modulation quality has certainly improved.