HF station monitor

[KL2ZZ]

I have a pair of DZ Kits HT-7 handy talkies, and just finished building the 2nd one. The final assembly steps for these things is adjusting three resistors and a varicap for the best sound and sensitivity. I've been doing this by ear with another receiver, but it's hard to judge what exactly I should be adjusting by the sound alone.

What I think I need is a station monitor. I see some Kenwood SM-220's and -230's on eBay, but these look like they're really meant for Kenwood equipment.

What sort of test equipment do you use to fine tune kit transcievers like these?

Thanks!

[N8YX]

Welcome to our Island!

I think what you're after here is a service (not a station) monitor. The Kenwood SM- series of accessories are in reality a low-bandwidth oscilloscope with a built-in line sampler and two-tone test generator. Useful for looking at your transmitted HF waveform or monitoring your rig's IF during receive, but as a general-purpose lab scope they're a little limited.

A good service monitor incorporates scope, RF and AF signal generators, spectrum analyzer and a number of other functions into one portable assembly. They're pricy - even used - but worth it.

Of course, one can do the same job with a bench full of separates. To set your HTs up you'll need a lab scope with a bandwidth equal to that of their highest covered frequency and an RF signal generator which covers the same range. A two-tone AF generator isn't necessary for your application but a single-tone device is. You'll need some way to generate a stable modulation envelope which can then be checked via scope.

An SM-220 could be used in a pinch but I think if you did a bit of judicious online or hamfest shopping you could find a lab grade setup for about the same amount of money. Head over to the Ham Radio Chit-Chat section of the site and look for my "Best kept secret" threads - specifically, the one which discusses Tektronix TM-500 stuff.

A TM506 power module, SC-502 scope, SG-502 signal generator, FG-502 function generator, DM-502A DMM and a DC-504 counter would give you everything needed to align a transceiver covering 20M and lower. You could possibly assemble the complete set for a few hundred bucks.

[wa6mhz]

I use my 200 Mhz O-Scope to peak circuit signals and observer any irregularities. Also, the 22 Ghz Spectrum Analyzer shows how clean the signal is (harmonics and Spurious emissions). An ordinary Ham scope (SB-610, SM-220, etc) are just good for telling U there is a signal there, but won't show much info on it. Nice to see when you are transmitting to see you are not splattering or producing Key clicks.

[w0aew]

Would it be easier to locate a local ham who would be willing to help? If he locates himself a few blocks away with a screwdriver or whatever tool is needed, you could both adjust the audio quality and just leave it at that. Wouldn't that be sufficient for a low-power, poor ERP 40-m HT?

[KL2ZZ]

Yeah, sort of. Figuring it out by ear is what I did with the first HT I built, but I could never get it just right. I could send a signal over a couple of blocks but I'd still be just trying to figure out if the dang thing is exactly on frequency, or maybe the mic gain is too hot.

I work in the computer business, and building many of the radio kits is a little more hands on, but a lot like "building" your own computer. Card A to Slot B, make sure those memory modules are the right speed, etc.

I still have a lot to learn about how the internals of a radio works, and I want to SEE what is happening when I change things.

Besides, I want to start building from scratch. I can tell my neighbor watches his plasma TV for much of the day. It would be a shame if I put together a transmitter that interefered with the enjoyment of his hobby, and a service monitor would help avoid that!

[N8YX]

Would it be easier to locate a local ham who would be willing to help?

If this was a one-off project that's exactly what I would counsel. However, it appears we have a budding experimenter in our midst:

I still have a lot to learn about how the internals of a radio works, and I want to SEE what is happening when I change things.

Besides, I want to start building from scratch. I can tell my neighbor watches his plasma TV for much of the day. It would be a shame if I put together a transmitter that interfered with the enjoyment of his hobby, and a service monitor would help avoid that!

If you're going to do anything with RF at all, you'll require a decent oscilloscope - and if building transmitters or power amplifiers you'll want a spectrum analyzer.

Can you get both on a budget? Sure. As far as separates go, have a look at a Tek 468, 475 or 2400 series scope (or their HP equivalents) and a 492 spectrum analyzer. I went the modular route and got hold of a couple 7603 mainframes plus a spectrum analyzer plugin, an assortment of timebases and vertical amplifiers, frequency counter/DMM plugins and a few miscellaneous units including a dual-channel sampling plugin. Depending on model, the sampling plugins will let you observe repetitive waveforms into the GHz region and higher on a 100MHz scope.

Unfortunately, you'll still need signal sources...the 7000 series gear didn't incorporate such offerings as a sweep or standard signal generator. That's where I would look to a 500 or 5000-series (preferred) power module and plugins. Scout around for an SG-5030, an FG-5010 and a DC-5010...plug 'em into a TM5006 and you'll have everything needed to do most RF work into the lower UHF region.

[AE1PT]

Alignments 'by ear' are a recipe for a whole lot of nothing. Believe it or not, the antiquated VTVM is still one of the best instruments available for peaking VCO, RF and IF alignment response. Get one, and a few probe varieties such as Demod, RF, and HV to go with it. My favorite is the RCA WV-98C.

[XE1/N5AL]

If you go for a surplus Tektronix 2465, 2465A, 2465B, or 2467B; be sure that the scope CRT still displays normal traces. Like many advanced oscilloscopes, they use custom ICs. On the scopes mentioned, there is a Horizontal Output chip that statistically experiences a greater than normal failure rate, causing loss of CRT traces (or greatly reduced trace length). Google "Tektronix U800" and you can read more about the failure problem. If this chip has gone bad, the scope is useless and you will have a very difficult time finding a replacement for it.

Edit: changed 2467 to 2467B

[AE1PT]

If you go for a surplus Tektronix 2465, 2465A, 2465B, or 2467; be sure that the scope CRT still displays normal traces. Like many advanced oscilloscopes, they use custom ICs. On the scopes mentioned, there is a Horizontal Output chip that statistically experiences a greater than normal failure rate, causing loss of CRT traces (or greatly reduced trace length). Google "Tektronix U800" and you can read more about the failure problem. If this chip has gone bad, the scope is useless and you will have a very difficult time finding a replacement for it.

Thank you for pointing that out. There is a lot of formerly high end lab gear out there that one with patience can acquire for a reasonable price. But unless one's game is repair and calibration of old lab gear--and is prepared to sift through enough junk to find high failure unobtainium LSIC OEM replacement components--it's best to stick to the common stuff that can be had very cheap.

[N8YX]

Thank you for pointing that out. There is a lot of formerly high end lab gear out there that one with patience can acquire for a reasonable price. But unless one's game is repair and calibration of old lab gear--and is prepared to sift through enough junk to find high failure unobtainium LSIC OEM replacement components--it's best to stick to the common stuff that can be had very cheap.

For all things Tek I recommend Tucker Electronics in Texas, QService in Greece or Barry Electronics in Canada. Ebay occasionally lists working custom Tek ICs for sale and I've refurbed a few pieces of gear by finding needed parts there.

Sad that one of their nicer scopes has this problem. Makes me feel better about my 7000 stuff, and there's so much of it available as surplus I doubt I'll ever run out of parts.