I have never aligned an FM radio and this morning thought I would give it a go -- no such luck. Maybe someone can tell me what I am doing wrong.

Using: B&K 415 Sweep Marker Generator and a Tektronix 7603 100Mhz scope.

I don't have the factory probes for the B&K 415 nor a manual - that probably is the #1 reason I can't get the response curve to show on my scope.

I set the B&K 415 to 10.7Mhz and connected the output per the radio alignment instructions through a "dummy antenna" .05uf capacitor. I used a straight through cable. That was the only connection I used on the B&K 415.

I connected my scope per the instructions in the radio alignment instructions. I could not see anything like the response curve or marker on the scope. What bandwidth range does the scope need to be set too?

Any suggestions is appreciated.

Thanks

Carl

Does the radio work otherwise? That is, does it only need an alignment?

If it is far out of alignment you may not see anything coming through the IF stages.

Yes, the Radio does work. I was thinking about a minor tweak tune up, and I was curious enough that I wanted to see the response curve on my scope.

Carl

Looks like I am a total newbie with this instrument.
More reading I find that I don't have the probes that work with the B&K 415 nor have I connected the Scope up properly. Looks like I need to connect both the vertical and horizontal channels of my Scope to the B&K415.

Here is a description of the probes:
http://www.cerant.com/Probes-B&K415.pdf

I can make all the probes except for the:
- Demodulator Probe
- 75/300 ohm RF cable
- IF Load block

Interesting instrument - just have no experience using it.

Carl

Just an FYI, not all FM radios used a 10.7 MHz IF. For example a Philco 48-482 is 9.1 MHz

Demodulator probes are usually just a diode and capacitor, and maybe a resistor; 1N34 should work.

The 75 to 300 ohm cable is just an impedance match; usually just resistors and maybe a cap.

I'm not certain what an IF load block is; probably a term that B&K came up with.

IF load block 4700 ohm resistor in series with a .1uF cap.

used in the above mentioned philco and others, its to load the if below critical coupling so it can be peaked correctly.

Am I going down the wrong road? I was thinking of updating my B&K 415 as follows:

- Replace the 4 MIC connectors on B&K 415 with BNC connectors

- Make a couple Direct Probes (S-4916)

- Make a couple 10K isolation resistor Probes (S-4915)

- Make an IF Load Block Probe (S-4918) -- 4700 ohm resistor in series with .1uf

- Make a Demobulator Probe (P-151) -- 1N34 and capacitor

- Make an RF Cable with with built-in Termination (75 or 300 ohms) -- ????
(wonder if I can use a 75ohm/300ohm Balum???)


Then again, is this worth the effort????

Carl

If you have nothing else to do FM alignment, then the answer is yes.