[NLRS] Parts is parts

[Dan Larson]

On Thu, 05 Feb 2004 11:30:27 -0600, Dr. Gerald N. Johnson, electrical engineer wrote:

>The PA and the driver module are almost certainly biased only for class
>C, not linear. 

Yah, I figured that out. The data RF Parts, INc. had on their web site 
lists the MHW820-1 as a class C device. 802-870Mhz.

>I think that PA transistor is probably operating in
>grounded base which makes linear biasing a lot more difficult. I suspect
>running the drive up to 902 the combination will put out power, probably
>only 10 or 12 watts.

Well, you're the Engineer, so I'll take your word on that. I am just being
overly pessimistic about it to be safe.

There is a ceramic block silver plated with holes in it which I am assuming is
a resonator / filter of some type, no doubt for the receive front end. I suspect
that it will roll off much more sharply.

>That's not a signal to be ignored, its a useful
>power level. 

At that frequency I am sure it is! I don't think I'd want my head too close to the
antenna though. I would like to avoid resonating my eye balls or other important
glands and organs that might resonate around 900MHz.

>Possibly trimming some of the PC board matching will get
>more power. I'm sure that neither the PA, nor the module cut off rapidly
>outside their specified frequency range. I don't see a Motorola RF parts
>data book near enough to the top of any of the piles about my computer
>to grab quickly.

Thats not a task I am willing to undertake alone without any useful test equipment
up in that range. 

>
>E.F. Johnson may have the manual for that radio available reasonably.
>
>Here's what I'd try:
>
>I'd run the transmitter up to 903.1 or 902.1 which ever is being used
>there. The multipliers may have to be retuned along with the synthesizer
>new programming. Then I'd add a keying circuit to the power control
>stage, to make it transmit CW with the modulation circuit shorted out.
>

Ok, now we're talking about taking over control of the PLL, right? 
That part I can handle. Without a schematic, I doubt that I am going to
do much to the VCO & multipliers, though, especially considering the 
aforementioned lack of test equipment.

>Oh, you want voice modulation? Then I'd run NARROW FM. If you keep the
>FM modulation index way down you get only first order modulation
>products and the signal bandwidth is the same as AM and is very copiable
>with a SSB receiver by zero beating the carrier. This scheme worked well
>on HF in the 30s and 40s and 50s (lack of amplitude modulation kept it
>from being copiable on unshielded and unfiltered TV sets and it was very
>simple to accomplish, no modulation transformers required), and worked
>fine on 2m in the Dallas area in the mid 60s. The theoretical support is
>that with first order FM modulation products only, the amplitude
>spectrum of the signal is exactly that of AM, the difference is that the
>carrier is 90 degrees out of phase from where it would be for AM.
>Phasing SSB rigs like the early Central Electronics had an FM provision
>where they developed double SSB with a balanced modulator then injected
>a phase shifted carrier to make it narrow band FM. They injected a
>carrier in phase with the carrier that fed the balanced modulator to
>produce AM. I thought the NBFM received in my Collins SSB receiver
>sounded better than the signals that were truly SSB.

Very interesting way of generating FM. Very different from modulating the
VCO / PLL. 

>
>For receive, tap off to an IF receiver after the first or second mixer.
>The FM receiver will he still linear at that point. Do the rough tuning
>with the PLL and the fine tuning with the IF receiver.
>

I've seen a similar scheme for obtaining SSB reception by tapping the IF
of the ICOM-R3 scanner.

THere are some 10.7 MHz filters in there, but I presume that is the second IF.
You are talking about tapping off of the first IF, right? I have no way of
telling what the 1st IF is without a service manual or something.

>By working CW or NBFM (and I worked my first 8 or ten states on 432 with
>a slightly modified RCA FM transmitter strip running CW) and using the
>front end as the receive converter (will need retuning, but I suspect an
>E.F. Johnson receiver front end will tune from 800 to 960 MHz at least)

*IF* that ceramic resonator at the front end doesn't get in the way. That 
thing has got to be pretty sharp.

I didn't take down the numbers stamped on it, but it started out with 802....

>you can have receive converter and workable transmitter all in one
>little box. Having an original manual that shows the differences between
>the various models for the available frequency ranges could make some of
>the frequency shifting easier to accomplish.

What do you suppose is the chance of obtaining a schematic or service manual?

>
>73, Jerry, K0CQ

Thanks Jerry!

73

Dan KC0LUY