Cheapo Frequency Counter Question

[Henry Finley]

For the last 3 years I've done a good many radio alignments with my Hickok 288X. And using one of these el-cheapo frequency counters . I've been happy by using one of the exact same model (attached) to  set my Hickok on frequency just before I hook it up to the radio. But it necessitates I first set the Hickok attenuation to full blast before the counter will lock on. Then reduce the Hickok output to more sensible output for the alignment. I had an idea to buy one of these cheapo wide band amplifiers (also pictured), to feed my Hickok into it to kick up the frequency counter sensitivity a bit so it can lock on frequency a little better. A lot of times by the time I get up the 30 or more mc, I have the dickens of a time getting it to lock on to the Hickok. Or any other signal generator for that matter. Will my idea of putting the counter on one of these wide band amplifiers be helpful? Thank you.

[blue_lateral]

You'll just have to try it and see if it is any better.

My guess is you will have way too much signal leakage and have to turn it way up and down anyway. The counter needs to be inside the generator to keep RF leakage under control, but if you put one in there after the fact, you screw up the shielding. The counter (and amp if used) need to be highly shielded too if they are carrying the signal. The connecting cables need to be double shielded and the connectors excellent. Otherwise the generator signal will just leak around whatever you are trying to align. The deck is further stacked against you because old service grade generators had a dirty waveform on purpose. It made them useful at higher frequencies than they could generate natively. But, which of the many harmonics coming from the output jack shall the counter lock on? There are many choices. The generator probably drifts too, so you have to keep jacking the level up to all the time to recheck frequency.

In my opinion save the Hickok for jobs that do not need that kind of accuracy. If you really don't want to use something modern maybe get an old HP 8640B with some issues and rebuild it. The counter is built in, it has phase lock (avoid the ruggedized military version because it doesn't), the shielding is very good and the signal level can go down quite low. The output is free of harmonics and can go to 500mhz or so. They are however 50 years old and you are likely to have some problems to solve. One caveat is they can only reach down to about 455khz, so if you find yourself aligning IF amps on a lot of simple AM radios and some of them have IFs lower than 455khz it might not be the best choice.

[theHWcave]

I assume you are using the PLJ-8LED counter? I have 2 of them and generally not seeing the "lock-on" issue. The counters have gain adjustment pots and it might be worth trying to adjust that. So, while locking on the signal generally works, I normally do not connect them to the signal output but rather to the sync output of the generator (if there is one). The problem is that the input circuit generally butchers the signal shape. Also note from the attached schematics (which matches my counters) that high frequency input and low frequency input are connected together which makes the signal loading/distortion worse. There are suggestions out there to separate the two by doing some surgery on the PCB. I have not done that, so no opinion on how feasible that is.

[Wallace Gasiewicz]

May I suggest buying an old freq counter.  We have seen demand and price for these go down in last few years.   
Less than $100 for a good one.  We have some sitting on the shelf at the radio shop for months without selling.   Possibly more people are using the nice cheap Spectrum Analyzers rather than a stand alone Freq Counter.   I suppose that is another option.   
I use a Service Monitor that is calibrated to a GPSDO, but these things are expensive.  (I think Service Monitors are worth the prices though) 
Heath had some nice counters and even old HP counters are cheap. I have both.Any instrument is only as accurate as their internal reference oscillator but that is usually plenty good for radio alignment.   
Some have facility for an external reference, which can make them more accurate.   
Consider one that meets your frequency requirements.  Heath had nice ones that will measure well over 100 MHz for FM radio work.  However most freq counters need a sizable input to work, some are more sensitive than others and some have variable inputs with attenuators. Spectrum Analyzers are much more sensitive.   

Usually I use a S9 signal for the input of radios that I am working on.  S9 is -73 dBm.   My HP counter will not show a freq until it has a -20 dBm signal and my Heath will read a -40 dBm signal  (at 30 MHz). No where near S9. The cheaper counters are probably less sensitive. The cheap spectrum analyzers can read signals far below these. I do not have any of the newer cheap SA so possibly someone may comment about the practicality.

Also, as I recall, the output from your venerable Hickok can be quite low at the higher end of the frequency output, If you put the RF amp inside the Hickok case, it may help the high end output.    There should be plenty of room in the case.   
I used two of the type of 50 ohm amps you have posted to amplify a 400 MHz signal that I needed. I used a SAW filter to limit the input to the amps to get the desired freq. It worked very well, I got about a 40 dB gain that I needed. If there are undesired more powerful frequencies on the input to any amp,  it may overload the amp and the amp may not amplify your desired freq enough..   

[Henry Finley]

referring to the last post above, what is a SAW filter and how is it used?

[Henry Finley]

Reporting back, I finished up my frequency counter idea and it didn't work. To make sure, here is how I wired it: The 9VDC positive went to the Vcc of the amplifier chip and the 9V negative to the ground. The signal from the signal generator went to the input side and the  frequency counter went to the output side. Since I didn't have any mini BNC connectors I soldered directly to the amplifier chip. The counter registered all zeros. So I had to cut out the amplifier chip and go straight to the counter. This means above about 19 MC's the counter can't lock in. One of the previous posts said there was a control on the counter to increase sensitivity, but there is no such control. You can adjust LED brightness and frequency offset. But not sensitivity. Disappointing experiment after a lot of work.

[theHWcave]

Hmm, can you provide more info and pictures of your counter module since it is obviously not a a PLJ-8LED?

[Wallace Gasiewicz]

SAW filters are commonly used in higher freq applications than you are using. I was mostly using it to block lower frequency signals that are mush larger than my desired signal.

https://en.wikipedia.org/wiki/Surface_acoustic_wave   

Your counter does not have sensitivity adjustment.  Even the ones that are adjustable have fairly high input power requirements compared to things like spectrum analyzers and even scopes.   I tried to elucidate that.
Apparently your amplifier is not doing anything. Do you know what volt supply you should be using?   

[Henry Finley]

Is this the input capacitor I should try shorting?