The AM Forum

i have a hammarlund hq-100 and was wondering if anyone could point me in the right direction to connect an old eico model 460 oscilloscope to my rx'er so i can see peoples waveform.

i figured i would ask here before i started googeling it so maybe someone with some experinece might be able to save me some time.

thanks
brandon.

Brandon, I grabbed the HQ-100 manual from BAMA.  There does not appear to be an if adapter terminal on the receiver, so you will have to cut directly into the circuitry.

What you really need is George Grammer's October 1953 QST article "Automatic 'Scope Monitoring of Transmission and Reception".  It tells how to build a scope, but more important to you, it tells how to connect any scope to your receiver. The article suggests connecting into the last IF amplifier grid or plate, but I think I would try an earlier stage first.  The more tuned circuits there are in front of the scope, the more an observed signal's spurious components are suppressed, so the scope won't give a true indication of a signals quality -- it will always look better than it really is.

The article has lots of good info.

73,

Al

Thank you sir. I had one part of a 3 part capacitor go out in the hammarlund yesterday. It causes a steady hum on rx no matter the audio gain setting.

i am waiting on permanent replacement capacitors for it now, and i am also doing a few little mods to it from here.

http://www.amwindow.org/tech/htm/hqaudiomods.htm

mouser usualy delivers fast so i would think i should have it finished up by this wekend. i also want to put a plug on the rx off the detector to feed a little audio amp i have for those arm chair copy nights.  ;D

In addition to the excellent article suggested earlier, if you have access to either a Heathkit HO-10 or SB-610 manual they will also contain good information.  Too bad they aren't readily available on the web anymore.

Basically you want to make a connection into the IF with as little circuit loading as possible.  You will still probably need to realign the stage to which you connect.

A scope on the receiver is of limited usefulness and hardly worth the effort.  The effects of the i.f. selectivity, internal and atmospheric noise, QRM, and perturbations in the ionosphere along the signal path including selective fading, usually render the pattern as displayed at the receiver to  have little resemblance to the signal as it is actually transmitted.

yea i am just haivng some fun with it. not lookin for anything more then that. thanks for the input though. i will keep all of that in mind.

I dunno, Don - WA2CYT (ccccrrrrappy......hhhhyelllowwy and...tinnnnny)a.k.a. The Dirkatron has been using one successfully for years to tell people whether or not they're signal is in PHASE. Probably the only time it wouldn't be of some use is when the band is in bad shape late night or those times when propagation just stinks. I'd think signal strength would be the main issue, not much to look at from a peanut whistle 100w rig on 75m during prime time.

The bigger problem would be interpretation or reports. Like audio, they tend to be pretty subjective.

I've never seen much usefulness hanging a scope off the last IF to view received signals other then for the "cute" factor. I'm not sure how CYT can tell if someone's audio is in phase just be looking at one of these scopes. However, I do find a panadapter-type scope hung before the first IF far more useful in looking at signals, band activity, adjacent channel interference, etc.

just fun to look at

WOW I can see out of phase voice on my "lash-up"....scope hung off of the I.F. outpoot immediately. Which reminds me to switch my microphone wires for the Fred Flintstone Show.

Don those $50 words of perturbations has me thinking..............

Fred

He can't. What he can tell you is if your "Christmas Tree" points to the left or to the right. That's all he's looking at, not the amplitude of positive vs. negative peaks.

Before I got a scope I could dedicate to monitor service, I found remote listeners with scopes had pretty good feedback for me (provided they knew what to look for, and what the limitations of their receive chains were). There's more than just audio phase to be determined from your scope pattern.

OK Thom,
you're getting very accurate in your statement coz even with the wrong phase I still see pos peaks, but will see severe baselining of the negative. Switch polarity and I'll see a LOT MORE positive peaks and neg peaks barely touching the baseline. The processing will protect the transmitter from severe overmod.

FRED