More Expert HRO Advice Needed!

[ashart]

In aligning my HRO-60, I've gone through the procedure to align the 455 kc I.F., seemingly ok.

However, the process of finding the correct I.F. frequency for alignment, involves finding the resonant freq of the crystal in the crystal filter.  My crystal shows a very sharp peak, so sharp that even a 10hz change in excitation frequency (HP 8657A) gives a noticible decrease from peak.  No other peak is evident.

All the IF transformers peak just fine, and all appears well, but:

The book states that the correct I.F. frequency is 453 to 457 Kcs.  My determined frequency is 452.84 Kcs.  

Need I be concerned with the IF being 160 cps out of the spec'd range?  I'm loath to take the rcvr all apart to clean the crystal, and the very sharp peak seems to indicate a properaly-working crystal.

(1) Do crystals drift over the years?

(2)  Might tuning the IF cans 160 cps away from the specified lower limit, cause any degradation of the IF response curve?

I'll appreciate all relevant comments, and thank you.


-al hart, w8vr

[Jim, W5JO]

Al the short answer is you are ok.  In your case the crystal drifted .16 Kc low, that is all.  Just align to that frequency and let it play.  Be sure of the tuning of the crystal filter.  That is  critical.

[ke7trp]

Yep. Your fine.  Mine was at 3.  I dont see any trouble.   Glad you are on the road to success with the 60!  I just got a Select O Ject for FREE. I should have it wired up to the HRO50T today.  I will have to take some video of it in action!



Clark

[k4kyv]

I wouldn't worry about a 150~ frequency error. Collins mechanical filters sometimes have more C.F error than that.

I think crystals do drift with age. Many of my old Bliley and Valpey crystals in the round holders are up to 1-2 kc/s off from the nominal marked frequency.  Of course, a 0.01% error with an 80m crystal is still about 400~.

[ashart]

Thanks, everybody - I'll ignore the slight discrepancy in IF frequency, and move on to my next problem!

-al hart, w8vr

[KA2DZT]

When that HRO was made you couldn't even measure frequency that close.  You're within a reasonable range of the IF's limits.

Fred