The AM Forum

Yep, probably a take off of a circuit from an ARRL hand-book...

But, a company called DZ Kits, is selling a 40 meter AM hand-held transciever kit..

What a riot!

Might have to get one, "just because"


Sure, 2 watts is LESS than piss-weak, but still would be more fun than a pair of Rat-Shack CB walkies!

Oh yeah... they're gonna have an 80 meter AM hand-held to....


http://dzkit.com/new_products.htm

I question the use of a DC RX for AM reception.

80 AM walkie talkie??

The military had one 60 years ago:

(http://amfone.net/Amforum/gallery/thumb_32_19_04_09_2_48_59.jpg)

http://www.kpjung.de/e_bc611.htm (http://www.kpjung.de/e_bc611.htm)


& frequency?  Why, 3885 kcs of course... 

Unless it includes a PLL to synchronise the oscillator to the AM carrier.

Looks like an interesting little company. I was looking at the assembly manual for their SWR kit and started laughing because it looks so much like the old Heathkit assembly manuals. I kept expecting to see the Heathkit logo on the top.

Who will be the first to work a QSO with a handheld on 3885?

You should read the "About" on their web site:
http://www.dzkit.com/about_dzkit.htm

I wonder if the novelty of the "new" 40m band isn't already wearing off. 

The past few days I have heard little, if any, AM on 7160.  The DX chasers scared everyone away?  Later at night after most Europeans have gone to bed, the band is sometimes still open for good solid stateside QSO's, especially to the west coast.  But I have heard very little west-coast AM operation on 40 since the band changes.

During the daytime I haven't heard much AM activity period, either near 7160 or 7290.  I fired up my automated CQ on 7160 about 1600 GMT this morning and ran several CQ's, and the only response I got (on what sounded like ricebox AM) was someone griping about how  long my CQ's were (the recording runs 2 minutes, then pauses for 30 seconds), but he apparently wasn't interested enough in a QSO to came back to my call or even to give his call sign.

And where are all the Euro-AM'ers?  I have yet to hear a single one of the 3705 crew anywhere on 40m AM.

French stations were allowed on 7.1-7.2 as of 29 March, but so far I have heard only one F-station (on SSB) period.

How do they expect anyone to receive AM signals on the HT-4 and HT-7 unless that direct conversion receiver is set up for synchronous detection?  I couldn't tell if it has that feature from their web site; the link to the manual is dead.

Last evening would have been great for stateside QSO. Lots of big signals, even from stations a few hundred miles away. It might have been one of the few times everyone in a rountable could hear everyone else.

Where are all those big AM mauls, KAYMOAN?

Hmmm.... Two minutes MIGHT be a little long for a CQ, I dunno.... ;D    On ssb or CW it would be, but maybe OK on AM.  Probably the ssb crowd down below 7200 aren't used to CQ's that long.

Anyway, I heard an interesting CQing technique from a Russian station the other day.  His used an automated tape on ssb, 40M.  What he did was repeat his call over and over and added in a CQ in once in awhile. It would pause every 10 seconds.  I found it very effective cuz if you're tuning the band, you would hear the callsign and wonder what was going on. It caught my attention and I called him. 

He got quite a bit of action with the 10 second calls and frequent pauses.  For you, it would go something like, "Calling CQ AM, K4KYV, K4KYV, K4KYV in Tennesee, Kilo 4 Kilo Yankee, Victor.... calling CQ AM and listening."  Pause for 5 seconds.  Then repeat the 10 second tape until an answer arrives in your AM inbox.

In contrast, I remember as a JN novice hearing some CW stations calling CQ CQ CQ CQ CQ for up to a full minute before giving their call and then repeating it all again before pausing. That was mentally abusive.   :-X


T

My digital recording AM CQ is 27 seconds long. The SSB CQ recordings 15 seconds. Back in the  "good old days" many AM CQ's could go on for many minutes before there would be a stand-by to listen. I generally tried to stay away from these types since , most likely, they would typically "old buzzard" each transmission if they made a contact. I didn't need any sleep inducement when I was on the air.

I emailed them and told them the link was broken.....

Supposedly it's working now....

Link works.

Notice the shape of their logo is the same shape as Heathkit?  I thought if you get something in a kit form to build it yourself it was supposed to be easier on your wallet than a commercial product ready for an appliance operator!

Ouch..  It is direct conversion... But, the RX uses a crystal ladder filter at the
operating frequency?????  AM, suppressed sideband reception?  No way to
QSY using that rig.  A deal killer.

Pete

Among other "oddities" I noticed he says that the total "AM power" is 1.5 times the carrier power when 100% modulated....


As far as price goes...pretty reasonable...
Once you consider the cost of a costom enclosure, having boards made, parts...
And let's not forget the R&D, and documentation time...


I think, though, I'll hold out until my class-e/pwm ammo-box project is done...
( PW 50cal.  ;D  )

I have a rare Midland 13-778 5W handheld 3 channel AM/SSB CB.  Never got around to converting it to 10M.  Might be fun for the next sunspot cycle, but it's probably worth more to a CB collector.  :)

(http://www.cbgazette.com/wt2_13-778_4sale.jpg)

"We'll do our best to provide new kits for you in the finest of Heathkit traditions."

Ahhh... that explains it Pete. Thanks for the link.

More RCA connectors?  :P

Nothing odd at all; that is the correct figure when modulating a carrier with a sine wave tone.  It takes a modulating signal at 50% of the carrier power to modulate a carrier 100%.  Therefore, a 100 watt carrier 100% modulated with a  sine wave tone has 50 watts of total sideband power, in addition to the carrier power.  That makes a total of 150 watts output power.

With high level plate modulation, it can be calculated the same way using input power.  100 watts DC input to the final requires 50 watts of sine wave audio power to modulate the carrier 100%.

With voice waveforms, the average power is much less, and the full 50% figure occurs only on instantaneous maximum voice peaks.  So the average audio power required for 100% voice modulation is more like 25% of the steady carrier power, but the modulator must still be capable of delivering 50% of the carrier power, without distortion, for the duration of the modulation peaks.  Just as in the case of slopbucket, because of the lower duty cycle of voice modulation, you can get away with smaller tubes and a lighter duty power supply than would be necessary for tone modulating a carrier 100% with a continuous sine wave at a 100% duty cycle.

Thinking in terms of high level plate modulation, the 50% figure can be derived mathematically from the fact that the instantaneous peak audio voltage and instantaneous peak audio current impressed on the modulated final at 100% modulation must be exactly equal to the steady DC plate voltage and DC plate current at the final stage.  The r.m.s. voltage = .707 X peak voltage, and r.m.s. current = .707 X peak current.  R.m.s. voltage X r.m.s. current = mean or average power (with a sine wave) = 0.5 X DC input power. 

Add the carrier power to the sideband power, and you end up with a total output power of 1.5 times the carrier power.