IC-7000 short term frequency stabilization

The IC-7000 is a nice HF+6m+2m+70cm-transceiver. But it has one stupid design flaw. The crystal oscillator which supplies the reference frequency to all synthesizers does not have any thermal insulation from its surroundings. Since it is a TCXO one can guess that Icom thought that its intrinsic temperature compensation is good enough. But they didn’t think about operating modes like FT8 where a drift of tens of Hz in a few seconds is a serious problem.
The main problem is that the fan is very close to the crystal oscillator and every time a transmission is started the fan starts blowing air into the transceiver. (At least when operating at 144 MHz, not always at HF it seems.) This creates a jump in temperature at the beginning of a transmission cycle, as well as in the beginning of the following reception period when the fan stops. For a tested transceiver, this temperature jump caused a short term frequency drift of some 25 Hz at 144 MHz over a few seconds, after which the temperature compensation in the crystal oscillator had pulled the frequency back again. This made it difficult to work FT8-QSO:s.
Fortunately it is easy to insulate the oscillator from the fan air by placing a piece of foam onto it. The crystal oscillator is mounted on the backside of the DDS board. This is accessible by removing the top lid and unscrewing the DDS-board screws. (One screw is shared with the fan, beneath the fan gasket.)
With a small piece of “double sided tape”, foam with adhesive, onto the crystal oscillator, the drift virtually disappeared.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s