EME157 2 & 6M PREAMPLIFIER KITS 
  Thursday 6th June 08

KIT CONSTRUCTORS ALERT:
KIT CONSTRUCTION NOTES:
KIT FAULTS & MODIFICATIONS:
PROTOTYPE TESTS:

EME103 KIT CONSTRUCTORS ALERT

There are no current issues to be announced.

The above Images show how the coils are wound for the 2M 144MHz version of the Kit. Takes note of the winding direction of L1 & L2 especially so that they fit the board correctly. On end on L1 is soldered to the turn 3 on L2. However this was found to not be all that critical in tests on a noise figure meter.

This Image shows the completed board before fitting the SubPC board & Relays

		These Pictures show how the Sub PC board is aligned to the main board & tack soldered into place. After you are sure that you have it aligned correctly, then solder it on both dises to the main board.

Modification to the first batch of EME157 circuit boards to fit a 6dB attenuator after the 1N5711 diodes to reduce the gain to around 16dB & add extra RF protection to the 1N5711 diodes & BF988 MesFET.

The above picture shows the completed Preamplifier ready to mount
in a masthead box.

Above chart shows the measured results of a prototype on a HP8970B Network Analyzer.

KIT FAULTS & MODIFICATIONS

 

1/  There can be various faults with this Kit which are mainly to do with construction. On one Kit we could not get the RX/TX switching circuit working. We found a 62ohm leakage from the gate of the 2N7000 fet to ground. We removed all components on that junction except the 680kohm resistor & still measured 62ohms to ground. We then removed the 680k & the 62ohm leakage disappeared. We can only conclude that it could have been due to something conductive on the board so we cleaned the board thoroughly & reinstalled the components. The RF sensing circuit can be tested by the small 1 to 2 second delay of the Relays engaging when the power is first applied to the Preamp.

2/  On later kits we have been adding a 6dB attenuator on the output of the preaplifier before the relay to reduce the gain & add more protection to the BF988 & 1N5711 diodes. Refer to the picture of the modification on the EME157 page. Some have complained of blowing the diodes & Fet when using up to 100 Watts on FM. The RF sensing circuit should not be used alone for high power, & a separate control voltage to the preamp should be used.

3/ Intermod problems don't seem to be an issue with this Kit & most problems can be directed to the receivers design. We recently have been using the preamp on 2M SSB with local & DX signals up to 60dB over S9 with sporatic E openings only some 10kHz away without any problems. We use a IC275H which are a rather reasonable receiver. Don't expect your TS2000, IC706 or 7000 etc to perform as good as the older receivers. I recommend turning the radios preamp switch off on late model Radios if you are going to use the EME157 2M preamp. On the IC820/821 the attenuator switch can be turned on when using the preamplifier at the Antenna.

4/ Some Radios are prone to producing a spike on the RF output when going into transmitt mode. This can be due to the ALC in the Radio not acting fast enough. This is a sure way to blowing the preamps diodes & BF988. You will have to hard switch the preamp as the RF sensing will not be able to cope with this high level of spike. If you have problems with the preamp being damaged then check on the Internet for any problems that may be associated with your Radios model.