Paul's current plan is derived from the approach that I have used in the past
that worked very well for 10M IF use. I started with a Vectronics DL300M dummy
load, HRO currently lists them at $50. The de-rating graph in its manual
suggest it should be good for 100W indefinitely (not sure I believe that). I
then drilled a hole under the SO 239 connector to accommodate a BNC. I then
connected the BNC via a pi resistive attenuator configuration. Even though the
big dummy load resistor didn't match the formula for the shunt input R of a
true pi resistive 50 ohm attenuator, it was close enough. And I don't recall
the R values I ended up with for the series and output R values, but they were
standard R values that were closest to what the pi attenuator calculator called
for. When I checked that attenuator it was in the vicinity of 25 dB, which was
close to what I was shooting for. I also suspect there may be some capacitive
coupling occurring as well. Again having a precision level of attenuation
didn't matter for 10M TX IF use, the DL300M modified into an attenuator was
good enough.
I then ran the IF radio at around 10-15W TX power. So even a worst case boo boo
of hitting it with 100W the transverter would only ever be over driven by 6-8
dB or so. No doubt the transverter output signal would be bad, but I don't
think that level of over drive would have let the smoke out either. The reason
I picked the 10-15W range was that I also wanted the IF radio TX power to be
somewhat above the lowest level that TX was capable, mainly to keep the
desired TX signal well above the quiescent broadband hash of the 10M PA. That
broadband hash would find its way into the VHF band TX signal.
At that time I was using Ten Tec Pegasus IFs that were minimally modified to
support a split IF. I was in fact running multiple RX IF radios on each of the
bands at that time. The N4PY control software allowed configuring the
transverter bands such that the TX power control when set to 100% was the 10M
10-15W level that I desired. It all worked very well and reliably.
I have since shifted all the IF radios to PC based SDRs including some HPSDR
Hermes boards, they work even better, and are super easy to mate to the
transverters.
Duane
N9DG
--------------------------------------------
On Sun, 2/5/17, Steve Kavanagh via VHFcontesting <vhfcontesting@contesting.com>
wrote:
Subject: Re: [VHFcontesting] FN55 - Transverter drive control?
To: vhfcontesting@contesting.com
Date: Sunday, February 5, 2017, 9:43 AM
Paul
Just one more approach....if you can source ordinary
resistors at a good price you can build your own power
attenuators for 28 MHz quite easily. It looks like 100 1
watt resistors would be around $30 from Digi-key, maybe 1/10
of that from Chinese vendors on Ebay. Each resistor is
probably somewhat inductive at 28 MHz, but with enough in
parallel the inductance is divided by the number of
resistors and becomes pretty much negligible. Here's a
100 W (or so) dummy load using that approach - the SWR is
great on 10m, but not so good on 6m:
http://www.qsl.net/ve3sma/HFDummyLoad.pdf
.
Occasionally I think about converting it into an attenuator,
but haven't gotten around to it yet.
73,
Steve VE3SMA
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