The New INRAD 2.8 kHz SSB Filter for the Drake TR-7
By: Jeff Covelli WA8SAJ email@example.com
The Drake TR-7 has a standard 2.3 kHz 8-pole SSB filter installed from the factory and many folks have ask if there was a way to increase the band width. Well, INRAD has just come out with the new 2.8 kHz wide SSB filter # 1714.2. This filter has a 1.7:1 shape factor which is about the same as the original 2.3 kHz made by Network Science back in 1978 when the TR-7 came out. It is a 50 ohm filter at 5645 kHz and will drop right into the original slot where the 2.3 filter is now.
INRAD info is: International Radio
Web is: www.inrad.net
NOTE: The filter cannot be used correctly unless the "carrier" set-points are done and the carrier "null" performed. This is very simple with the pictures and description provided here. If not done the side-bands will be into the opposite side and will not sound very good.
Assuming the TR-7 you have is already aligned or at least works like normal, you only have to "tweak" two pots located on the regulator board on the front right side of the TR-7 and one more pot after those two are done.
Here is the procedure for alignment: Have the TR-7 in a dummy load before adjustment.
1) On the TR-7, set the radio to 14 MHz band and "push" the DOWN button to select the band for alignment with the volume up and "MODE" switch in "USB" first. NOTE: Make sure the pass-band button is in the "OUT" position when doing this!!
2) Dial up 13.693.3 MHz on the readout and set the "USB" pot for "ZERO BEAT".
3) Next, dial up 13.696.7 MHz on the readout and set the "LSB" pot for "ZERO BEAT".
4) Turn the microphone gain down and now set the "CARRIER BALANCE" pot for lowest signal in LSB and USB using another receiver dialed to a ham band on the 14 MHz band. Adjust so the balance is about the same on both side-bands. Usually they will be.
5) This sets up the new 2.8 kHz filter in the correct pass-band since it is wider than the 2.3 kHz filter. Your filter will start at 300 ~ and up to 3100~ which is 2.8 kHz wide now.
6) You can use the old 2.3 kHz filter in one of the 3 receive slots and have extra receive selectivity using the pass-band tuner.
7) Refer to the pictures provided for a better look at what you are adjusting for the new 2.8 kHz wide filter, and enjoy!
73, Jeff Covelli / WA8SAJ