24 March 2015

Front-end saver for LB antennas


If You are using a separate receive antennas then you need a good protection circuit to eliminate the possibility of blowing out Your receiver's front-end while using these auxiliary receive antennas specially on low bands.

The protective circuit should be designed to disconnect the receive antenna during transmit, ground the receiver input when transmitting thus keeping RF out of your radio and eliminating the chance of blowing your radio's front end.

The perfect solution designed years ago Gary, KD9SV and I am using this genuine design in the alu-box for years without any problems.
Now I need more of these circuits because of more radios is planned in the ham-shack (SO2R etc.) and also the contest team OK5T need to improve the low bands setup...

Thanks to Martin's (OK1RR) work I was able to use his slightly redesigned Front-end Saver based on KD9SV design using his PCB layout.

Very well designed PCB with one-side bus wiring is easy to assemble and it will work for the first shot if you will not make the mistake...

The suggested PRMA 1A12 relays > molded rugged construction with an internal protection diodes are used.

Steel painted box from local electronics shop is used in order to save building time and it does not look so bad.

Update 17July2017
There is not necessary to use the 2N2222A in metal TO-18 package! It is possible to use plastic TO-92 package as the most of parameters are same and there is not impact for that application. Most important is to identify the correct pin-out of your device!

There is several manufacturers producing several different versions like 2N2222A, P2N2222A, PN2222A etc. and the pin-out is NOT the same or standardized!

Check carefully your purchased version of transistors and identify the correct pin-out before you will assembly in order to avoid FES malfunction!

On picture above is an example of correct orientation of KSP2222A-E19 transistors TO-92 package on PCB...

After the final assembly I am highly recommending to test the device for its correction functionality. It is much better to spend few minutes more instead of damaging you transceiver front-end because of non-working Front-end saver...

The short theory of relays operation in this circuit is here:

State nr. 1
(QSK T/R is floating)
Re1 - closed
Re2 - open
Re3 - open

In this case ANT port is connected to RCVR input port and AMP KEY port is floating.

State nr. 2

(QSK T/R is grounded)
Re1 - open
Re2 - closed
Re3 - closed

In this case ANT port is disconnected/floating, RCVR input port is grounded and AMP KEY port is grounded too.

According to the theory of operation described above you can make easy and quick test using DMM before you will connect it to your radio and antenna.

1. Apply the 12V DC power to the circuit.

2. Check with DMM that ANT port hot pin is connected to RCVR IN port hot pin and that AMP KEY port hot pin is floating.

3. Using the tweezers or any similar tool short the hot pin of the QSK T/R port to ground.

4. Check that you are able to hear switching clicks of the relays when you are shorting the hot pin of the QSK T/R port to ground. Be very attentive as the chattering of relays is very quiet and fast so it is hard to hear in noisy environment. 

5. Check with DMM that in that state the ANT port hot pin is disconnected from the RCVR IN port (refer to point 2.) and it is floating. Then check that RCVR IN port hot pin is grounded. Finally check that AMP KEY port hot pin is grounded too. 

Update 18Sep2017
Some of the people asked me how to implementing this FES into the Icom radios setup. So here is the layout example for wiring it together with Icom transceivers. (just quick pencil drawing...)

The "PTT output" port on the drawing means port on your transceiver where hot pin goes to ground while transmitting to control external equipment. In our case the FES. On the Icom radios this port is labeled as "SEND"!

See port 10 marked as SEND. This is your PTT for wiring it with FES.

The "Ext RX ant IN" on the drawing means port dedicated to connect an external receiving antenna to your transceiver. On the Icom radios this port is marked as "RX ANT"! See port 1 marked as RX ANT on the Icom rear panel picture above.

Do not hesitate to ask for details if you need but all is clear from the pictures and circuit is pretty simple. Also let me know if you want to help with PCB or even with PRMA 1A12 relays for building your own FES...

With courtesy permission from Martin,

73 - Petr, OK1RP

18 March 2015

RSGB Eclipse QSO Party 2015

good time to remind, because it is this Friday, March 20th...

The RSGB Contest Committee announces an "Eclipse QSO Party" in cooperation with the Propagation Studies Committee during the partial eclipse on the 20th March. Information about the experiments being carried out and links to other relevant sites are here

This is not a contest, but some of the RSGB Contest Committee software and web facilities will be used to collect and display activity reports.

The D layer of the ionosphere may not be as strong due to the eclipse, and stations on the lower bands – 1.8 MHz, 3.5 MHz and perhaps 7 MHz may be heard that would otherwise be inaudible during the day.
All available radio amateurs are invited to participate -- this is an opportunity to contribute to our knowledge of propagation and the ionosphere.
Those who wish to participate but cannot operate on the day of the eclipse may contribute if they have automatic skimmer / wideband RX (e.g. SDR) facilities. Please record the QSO Party and contact the Contest Committee to submit your recording.

See You on the air,
73 - Petr, OK1RP