RA 17/40 mHz IF

[bavradio]

Hello all, This is my first thread, so be gentle if I trip over myself.
I just read an old thread about sweep alignment of the RA 17 40 mHz IF. Shortly after buying my first RA17(L), I sought out a Wlitron 910D with the proper plug in for 40 mHz ( it's 100 kHz to 110 mHz? ). Keith's Racal site mentions using this generator for the RA 17 but the section is unfinished and there's no email for him.
So, here I am and here's what I tried. (feel free to laugh at this procedure)
I disconnected the 40 mHz strip at both ends, connected the Wiltron to the input, connected my Tek 454 to the outout through a diode/ capacitor detector,connected the trigger output to the trigger input. and adjusted the sweep for a bandpass looking waveform. I then set the generator to the delta f mode at 40 mhz (F1-F2 didn't give me a discernable hump like I thought it would) I monitored the cw frequency with a counter. So I then tweaked away and re- tweaked till I got the classic looking ramp with the plateau and ramp down on the right end picture.I didn't even power up the RA 17 for this.
I only paid $100 for the Wiltron , so if I'm barking up the wrong tree it's no big deal. Reassembling the radio and testing it revealed no improvement in it's operation which leads me to believe that I didn't make it worse and that my problem is elsewhere.
I really would like to perfect the (a) technique for this alignment procedure in the abscence of a CT501 or Polyscop, or maybe fork up the $$ and buy one of those. This can't really be brain surgery.... can it? Thanks for listening to my mindless rant! Ross 73's W1EKG

[XTC]

From what you say, the Wiltron should be capable of sweeping the filter. A description of the procedure and the curves you should see is given on the recelectronics site.

However, the 40MHz filter is a complicated beast with eight presets to adjust. If you've just bought the Wiltron, it would be an idea to make up some filters and sweep them so that you have a feel for it. Using it to align the 40MHz BPF right off the bat seems like jumping in at the deep end. If you are going to adjust it, mark the positions of the screw slots with a pencil before starting, that way you can reset it to the original state if you get lost.

CT501s are expensive and hard to find, and I don't really see why the Wiltron shouldn't be as good. What's that diode detector like? It may be causing you problems.

The general view here is that the 40MHz BPF rarely gives problems. They were set up in the factory by people who sat there doing it all day. I don't think that setting them up is brain surgery so much as something needing experience, like adjusting the float screw of a multiple section tuning cap. The screws rarely need adjusting and fiddling with them just for the fun of it causes more problems than plenty.

Pete.

[MichaelR]

When sweeping filters the primary rule is to make sure that you do not sweep too fast. Too fast a sweep speed will give you false response shapes.

Moreover you are making a scalar measurement. The detctor is seeing all of the RF it is not frequency selective . For instance if you look at the bandpass response shape and there is an anomaly at say 40 Mhz the detector may not be seeing just the 40mhz from the sweep source it could be seeing a subharmonic/harmonic out of the sweep source that is occuring at some other frequency.

mike

[bavradio]

I picked up a spectrum analyzer today. It covers 1-1,000 mHz. I'll keep you posted... Ross