[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: RE: 2m to 10m to 70cm converters



High-power varactors are very hard to obtain and 1N4148's generate only tens
of milliwatts. The cheapest solution today may be a direct conversion
transmitter using the T1 kits from Kanga US, followed by some RF
amplification. Kanga doesn't supply VFOs for frequencies above HF, but the
ARRL has published designs.

I'm laying out some boards for the OFDM modem project that consist of a
VCXO, delta-sigma PLL, VCO, quadrature modulator IC and two MMIC amplifiers.
These are intended to take the baseband output from 2 DACs and generate 100
mW of RF for the 70 cm band. The VCO specification shows -104 dBc/Hz phase
noise at a 10 kHz offset and the quadrature modulator specification is 34 dB
minimum opposite sideband suppression, so they could be used as an SSB
exciter if combined with the audio phase shift network that Kanga produces.

There are pin-compatible VCOs and quadrature modulators for 400-2500 MHz so
this may work for other satellite uplink bands. I've got an audio phase
shift board in my junkbox so I'll try it when I get boards back.

73,

John
KD6OZH

----- Original Message -----
From: "Robert Bruninga" <bruninga@usna.edu>
To: <amsat-bb@amsat.org>; <pe1rah@yahoo.com>
Sent: Sunday, June 05, 2005 16:24 UTC
Subject: RE: RE: [amsat-bb] 2m to 10m to 70cm converters


> >>> William Leijenaar <pe1rah@yahoo.com>
> >The biggest problem is only to get from
> >HF on 70cm uplink.  These upconverters from
> >28MHz to 435MHz are very rare and...expensive.
>
> But they dont have to be I dont think.  Remember
> the old high-level varactor diodes.  Just one
> active part.  Hit it with plenty of power at 14
> MHz SSB and plenty of power at 449 MHz
> carrier from two rigs and then filter the resulting
> RF mess to only pass 435 MHz and you should
> be able to get a few watts there.
>
> In fact, I thought these days if you cant find the
> old high-power varactor diodes, that  you can
> simply parallel say about 36 1N4148's to handle
> the power and do the same thing.
>
> This depends heavily on people building the
> good filters on the output to keep all
> spurrs down.  But it should work.  This high-level
> mixer doesnt even need a power supply.
> It is totally passive.
>
> I'd love to have time to experiment with this,
> but alas, no time...
>
> de Wb4APR, Bob
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home