[HBR] Re: W1KLK receiver

[N2EY at aol.com]

In a message dated 8/18/2004 10:26:21 AM Eastern Daylight Time, waltah at earthlink.net writes:

>Jim said:
>> Agreed but I read the article a bit differently.
>> 
>> I think you could get adequate image rejection without all those
>> tuned circuits. What 'KLK wanted was not just image rejection but
>> rejection of strong out-of-band signals - meaning anything more
>> than a few dozen kHz away from the desired signals. If the signals
>> don't reach the mixer, it doesn't have to deal with them. 
>
>Yep.   For 80M, however, he probably could have used the 7360 
>mixer 'barefoot' and done even better; there's no serious problem 
>coupling two or three tuned circuits without a tube between if you 
>are only covering 500 kcs at 80M. 

I'm not sure about that. He'd still need 4 tuned circuits between antenna and 7360 grid to get the kind of RF selectivity he wanted. Aligning such a monster would be difficult; with the quiet, low-gain GG 7044 he gets isolation between the two doubletuners. 

I have seen exactly one 7044 in over 30 years of looking. I bought it. Possible subs are 5687 and 2C51. Note the unusual basing of these tubes; they are tailormade for pushpull or GG circuits, unlike most dualtriodes.
>
>I don't know what the ultimate sensitivity of the beam tubes is as 
>mixers but it's pretty good.   I've got 0.25 uV on 40 meters with no 
>RF stage and two tuned circuits preceding the mixer.  

The SquiresSanders article says they got less than 5 dB noise figure from a 7360 mixer - on 10 meters!

For a single 
>band receiver you could use a push-pull 6J6 oscillator, with 12AT7 
>cascode buffer if needed (probably not) -- the design should be a 
>cinch.

You need a pushpull tuning cap, too.

SS used a balanced transformer to drive the 7360 deflectors. With modern toroids and a buffer stage, a bifilar link might be the way to go. Or a phase splitter.

>With just one oscillator he wouldn't have the problems I 
>have with spurious responses.  

G3PDM (or was it G3DPM) has a design in one of the RSGB handbooks of that era. Dualtuner straight into a 7360, xtal filter at 1680 kHz, etc. His solution to the LO problem was interesting:

The actual LO is a dualtriode balanced oscillator, directly driving the 7360 deflectors. It is varactor tuned.

He has a very stable VFO which is premixed with the output of an xtal het osc. This output is compared with a sample of the balanced LO, and the error signal drives the varactors in PLL fashion.

No digital stuff - all analog, mostly hollow but with a few sandstate devices like a UJT that sweeps the LO if phaselock is lost.

No specs on phase noise but pretty slick for ~1968, doncha think?
>
>The purest would probably use both 'top' coupling for the front end 
>coils (with a small cap between the tuned circuits) and 'bottom' 
>(with a shared small coil at the bottom so the gain could be leveled 
>across the band.

It'd be a mess to align, tho.

   In a bandswitched receiver you run out of space 
>pretty fast with so many parts but for a single band it's surely not a 
>problem.

Bigger chassis. If we want small we can just go buy a rig. 

About 1964, W9BRD's DX column carried a tale where he talked about miniaturization. His criteria became whether or not the shack cat (Madame Mu, a Siamese, though her name is done with the Greek letter) could perch atop it. 
>
>An interesting design would be plug in front ends, with different 
>VFOs according to the band.  You could even use different 1st IFs 
>and convert to a common IF to do most of the amplification in the 
>mainframe.   Four tubes, maybe, in the plug-in unit and the rest on 
>the mainframe. 

It's been done. The metalwork is the real killer. Turrets are one solution.

One idea I've toyed with is to have a common VFO/IF, but separate frontends and matching transmitters for each band. 
  
In QST for 1971, a 160-6 meter transceiver was described (the ATR-166). Used the Heath SB het scheme, 898 dial, some really good ideas. Had features you could not get in an SB line. All in one box. You changed bands by swapping modules - RF amplifier, driver, heterodyne oscillator, final tank. It was the inspiration for the Southgate Type 5 and Type 6 transceivers, one version of which still exists. 

>
>> If I understand the process, we hams measure 3rd order IM by injecting two
>> relatively close-spaced signals into the rx and raising the level until an
>> inband distortion product shows up. Typically it's two signals 20 kHz on
>> 20 meters. 
>
>With practical front end tuned circuits testing at 20 kcs spacing on 
>20M tests only the mixer because the practical Q's give you no 
>help rejecting the unwanted signals.   On 80M, both the front end 
>coils and the mixer are tested.   Both tests are of interest.
>
>That actually works out pretty well because there's usually a much 
>bigger problem with IMD on 80M than on 20M. 

My point is that many rxs inhale so many MHz that IM troubles may be caused by signals hundreds of kHz away. 
>
>On the HBR-4 project, I hope to get 30 and 20M working today.   
>The Butler oscillator is actually working reasonably well now, 
>though I am going to go crazy with the retuning all the crystals 
>every time I move that trimmer board to add another band or two.  
>Those 50 mmf trimmers tune so sharply on the high bands that you 
>really have to hunt for the crystal frequency.

I just yanked plates off them...
>
>An additional problem is tuning drift, probably due to heating of the 
>toroid.  It usually takes a couple of retunings after each change to 
>find the point at which the CO will *keep* working as the set warms 
>up.  There are higher stability cores available; I may have to look 
>into that.   Or I can just use a slug tuned coil with a VHF core -- 
>that's probably simpler.

That's a lot of trouble for a crystal oscillator!

I shall dig up one of my old flyers from C-W Crystals 

(moment of silence in memory of a friend I never met)

which has most of the circuits I use, and get that info to you.

73 de Jim, N2EY