DEMI transverters - questions and WTB
Clay W7CE
Unfortunately, the kit was missing two trimmer caps and an inductor so I
have to wait for the parts to show up before I can complete it. In the
meantime, I'm thinking about painting the outside of the aluminum case and
heatsink black. Can anyone think of a reason why painting it might be a bad
idea? I don't have a particularly good reason other than I think it will
look more finished with a paint job.
Also, I'm thinking about ordering 25W 33cm and 23cm transverters from DEMI,
but they are only available fully assembled. Does anyone have recent
experience with their actual shipping times for completed transverters?
Someone (can't recall who) told me at Seaside that they had been waiting 8
months, even though the original quote was 2 months. I know my 222 kit was
quoted at 2 weeks and took over 2 months to arrive last spring. I'd like to
place orders now, but would like some degree of confidence that they'll show
up before the June VHF contest. If not, I need to look at other options.
If anyone has a DEMI 25W 33cm or 23cm transverter (kit or assembled) that
they'd like to sell, please contact me.
73,
Clay W7CE
Edward Cole
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Clay,
I was surprised to see that the 33cm and 23cm transverters were only
available assembled. I was thinking of getting a 60w 2m xvtr from
them and I see that the 2m & 6m line is under redesign, so who knows
how long it will be till they are available, again. I can say I got
rapid delivery of my 10-4 board kit. I ordered on the evening of
Dec. 18 and Steve and Sandra were going on vacation Dec. 19-Jan.
3. I was pleasantly surprised to receive the kit last week. I
suppose they had them in stock and sent it out the day they left on
vacation. I was happy that it came so fast as I have received a
PLL-VCO for my 1296 xvtr and want to use my Rubidium as
reference. The 10-4 splits the output 4-ways.
So have no idea what to advise regarding DEMI. I sent my circa 2000
144/1296 xvtr to them for repair this fall and it came back in about a month.
I would guess painting the outside of the enclosure should prove no
problem. The diecast enclosure will retain good grounds with
connectors on the inside surface. You do need to tape off the
connectors to avoid painting them (Of course).
73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
500-KHz/CW, 144-MHz EME, 1296-MHz EME
DUBUS Magazine USA Rep dubu...@hotmail.com
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Mark K7HPT
impression of the DEMI 222 transverter and did you also get your 33cm
transverter form DEMI or SSB. I would like to add both bands to my
station and have looked at both websites. I would appreciate input
from you or any one using transverters.
I keep seeing the Motorola 900 cell phone amps on eBay so I got one.
$20 for 150 watts I thought was cheep. Is anybody using these amps on
900 MHz?
Thanks,
Mark
K7HPT
Marshall Williams
1)Advertised as 150W, actually makes 105W after conversion. Requires about 2-3W of drive.
2)Advertised as 300W, actually makes 250+W after conversion. Requires 5-6W of drive.
3Advertised as 600W, actually makes 400+ W after conversion. Requires 50-150mw of drive. Yes mw.
Conversion articles for all three amps are on www.vhfsouth.com under Tech Info.
Eric(that is white bus Eric) has some of the "600W" units. The "300W" units make great amps and they are only $50 on eBay. Conversion of the 150W and 300W units is very easy. The conversion of the 600W units is also easy, but more difficult than the first two. I have converted about a dozen of the 150 and 300W units. If I can do it, it must be easy.
Some advice....these units are rated for +26V NOT +28V. However, I know that some are being run at +28 and they work OK. You pays your money and you takes your chances there. What we do is to put a deep cycle battery in series with the car's electrical system--that is +12V + 14.6V = 26.6V...this works perfectly in the rovers. In the home station, get a +28V supply and turn it down to +26V....easy.
There is a problem now with 1) and 2). The new DEMI transverter puts out only 0.5W. That will grossly over drive 3)[you can turn it down with the internal pot], but it is not enough drive at all for 1) or 2). The older DEMI 902/3 transverters put out 10W and were perfect for 1) and 2)--you just had to turn down the drive with the internal pot. I don't know how to solve this one other than to try to purchase one of the "older" DEMI transverters that put out 10W.
You will be very happy with the Motorola amps on 902/3. They work perfectly and after conversion are "no brains necessary" in the operation department. They just work.
I hope everyone did well in the contest. We did not. Propagation was absolutely terrible here and Murphy came early and set up residence here. We had several equipment disasters just before and during the contest. This was our worst Jan in several years.
73 Marshall K5QE
Clay W7CE
First, thanks for the activating DN16 and DN17 in the contest. I heard you
several times on 1296 while you were in DN17 on Sunday morning. Local QRM
prevented me from being able to work you though (it's not often we have to
fight QRM on 1296).
The 902 transverter is an older SSB Electronics LT33S which is no longer
manufactured. Shortly after I got it, the PA failed and I was left with the
driver stage which provides about 1/4W out. The transistors are no longer
available, so I've been pondering how to use it. Marshall, K5QE, mentioned
to me that the Motorola 600W units only require about 100-150mW of drive, so
I bought one of those from Eric, KB7DQH. I removed the old PA from the
LT33S, brought out the driver output to a BNC on the rear panel and things
are working great (until I get a bigger power supply working, I am running
80W output). I believe the 150W amp that you have also can be driven with
fairly low power.
For 222, I'm using an FT-736R, but I recently built a DEMI 222 transverter
kit to use with my Flex 5000A transceiver. It is functional now, but the
output power is low. I traced the problem down to low gain in the final
driver stage before the PA. I need to remove it from the case tomorow and
do a visual inspection to see if there is anything obvious (the MMIC is
mounted on the bottom side of the PCB). I suspect it will be something
simple or a defective MMIC, so I should have it up to full output in a week
or so. Currently I'm only getting about 4W out when I should get at least
25W. I had it on the air just before the contest and received good reports
on the audio quality.
There were a couple of issues with assembling the DEMI transverter. First
problem was three missing parts that DEMI promptly shipped to me (4 day
turnaround). The next problem was incorrect instructions based on small
construction changes that weren't documented (no errata of any kind in the
kit). In one case, there was a jumper required if one of two options was
installed, but the instructions only indicated that it should be installed
for one of those options (I have the other one). And the instructions were
generally vague about exactly what needed to be installed based on which
options were installed. I spent a couple of hours really studying the
schematic and my options to make sure that I was assembling it correctly.
The only other issue during initial testing is frequency stability. The LO
drifts rapidly for the first 10 minutes or so and then slows down and
continues to drift for a long time. I haven't fully quantified it yet, but
after several hours in standby, the frequency has drifted a few hundred
Hertz. I will probably go to a PLL-based LO that is locked to a stable 10
MHz reference.
One final note: I bought my DEMI kit about 9 months ago. Since then,
Downeast has discontinued all transverter kits below 902 MHz (some have been
unavailable for over a year now). There is a link on their home page
discussing their new transverter design that they claim will be available in
March or April. I'm not real hopeful that they will actually make that
schedule based on past performance. However, the new designs look really
good and I they will be worth the wait. Despite the minor issues, I plan to
order DEMI 902 and 1296 transverters to use with the Flex 5000A.
73,
Clay W7CE
Thanks,
Mark
K7HPT
--
Edward Cole
Thanks for the heads up on 26v vs 28v. I will be installing a 28v - 50A supply at the base of the tower so probably will have a little voltage drop 50-feet up the tower. The PS will supply a 500-KHz linear and maybe other amps (2304?), some day.
My recent progress is getting the Efracom LPRO-101 Rubidium reference unit installed and distributing 4-ways. I have my EIP-538 mw counter locked and soon to have my DEMI 144/1296 xvtr locked using an Israeli PLL-VCO. I have a webpage for the Rubidium:
http://www.kl7uw.com/Rubidium.htm
73, Ed - KL7UW
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73, Ed - KL7UW, WD2XSH/45