On 8/30/2011 8:29 AM, Geoffrey S. Mendelson wrote:
Allodoxaphobia wrote:

We still don't have a clear description of what the OP is trying to
accomplish.

Take two radios, two j-poles and a lot of coax and make a repeater.
Obviously I will need some sort of controller in between but that's
irrelevant.

I want to place one J-pole (or similar antenna) at one corner of my garden,
and another at the other one (10 meters apart).


This will actually help a bit

The free space attenuation for 10 meters at 144MHz is
32.4+20*log10(0.01)+20*log10(144) 32.4-40 +43.2 = about 36dB.

If your Tx is 20W (+33dBm), then the receiver is going to see about
-3dBm at the Tx frequency. If you want to get the Tx signal down to
around -40dBm or so, you only need 30-40 dB of attenuation at the Tx freq

Then there's the Tx phase noise to worry about. Figure it's 60dB down,
so +33-60-36 = about -63dBm.. probably enough to completely mask any
received signals (what's your sensitivity.. -130dBM?) so you need a
notch with 70dB rejection on the output of your Tx.

You're 600kHz away, implying you need a Q better than a few hundred.
If you just tune up some of those cans for that, and the Q is too low,
then you'll be attenuating your transmitter.


Any reason why you're using a split of 600kHz? Why not go to a
non-standard split to make life easier. Pick two frequencies 3 MHz apart
(assuming you can get them coordinated, which is more a political than a
technical issue)

One will be used to receive a signal, the other to relay it. They both
will be somewhere on the 144-146mHz band, with the output being a few watts
with a max of 20.

Besides the distance, I was looking for a cheap way of not having
the transmitted signal block the receiver. The duplexer in question
is rated at 75dB isolation with a 3.5mHz split, I can only have .6 mHz.

What I was wondering is that since at a .6mHz split, the isolation will
be a lot less, can I somehow combine the two sides to make a better
filter?

Thanks,

Geoff.

Jim Lux wrote:
Any reason why you're using a split of 600kHz? Why not go to a
non-standard split to make life easier. Pick two frequencies 3 MHz apart
(assuming you can get them coordinated, which is more a political than a
technical issue)

Don't forget that in Region 1, the 2M band is only 2 MHz wide, the
bottom 500 kHz is dedicated to SSB and the top 200 kHz is for satellite.

On 8/30/2011 11:14 AM, Rob wrote:
Jim wrote:
Any reason why you're using a split of 600kHz? Why not go to a
non-standard split to make life easier. Pick two frequencies 3 MHz apart
(assuming you can get them coordinated, which is more a political than a
technical issue)

Don't forget that in Region 1, the 2M band is only 2 MHz wide, the
bottom 500 kHz is dedicated to SSB and the top 200 kHz is for satellite.

Sure, that does make it harder. The OP is in region 2, though, where
there's 4 MHz theoretically available)

flame protective suit on And of course, a lot of the band plans are
basically gentlemen's agreements and have no force of law. As long as
you don't interfere with someone (challenging in some geographical
locations), you can pretty much do what you want.flame suit off

I wouldn't want to put input or output on 144.2, for instance.

But looking at the ARRL band plan, you could put your input up at
147.6-147.99 and put your output at 145.5-145.8 (Misc and experimental,
per ARRL).. not quite 3 MHz, but close, and a whole lot better than 600kHz.

Here in the Los Angeles area, either TASMA or the anti-TASMA folks would
probably round up people to have you tarred, feathered and run out of
town on a rail, no matter what you do. In any case, things move so
slowly that unless you were hideously inconsiderate and egregiously
interfering, you could probably run for a year or more before it would
get too nasty.

There is a 147.585/144.930 pair labeled for "portable repeater" in the
TASMA plan (max 72 hrs/month).. that's 2.5 MHz apart (to make filtering
easier). They also say 144.310-144.375 is for simplex unchannelized,
but I've not heard much on the air there..for an experiment, it would
probably work.

Jim Lux wrote:
On 8/30/2011 11:14 AM, Rob wrote:
Jim wrote:
Any reason why you're using a split of 600kHz? Why not go to a
non-standard split to make life easier. Pick two frequencies 3 MHz apart
(assuming you can get them coordinated, which is more a political than a
technical issue)

Don't forget that in Region 1, the 2M band is only 2 MHz wide, the
bottom 500 kHz is dedicated to SSB and the top 200 kHz is for satellite.

Sure, that does make it harder. The OP is in region 2, though, where
there's 4 MHz theoretically available)

I think he is in Region 1. He posts with 2 callsigns, one is a 4X1
(Israel) and mentions:

but my 2m band is only 144-146
mHz, and the repeater portion is really just 145-146.

flame protective suit on And of course, a lot of the band plans are
basically gentlemen's agreements and have no force of law. As long as
you don't interfere with someone (challenging in some geographical
locations), you can pretty much do what you want.flame suit off

Sure, but to get a permit for unattended operation, at least over here,
you'll need to abide to the band plans.

(in fact in my country, Netherlands, it is even worse: the repeater
frequencies are not coordinated by the ham community itself, but by
the equivalent of the FCC. they work strictly by a set of rules
originally drafted by the amateur societies, in the days the bands
were still overcrowded. arbitrary figures were put in those rules
regarding things like minimal desirable distance between repeaters,
maximum height of antennas, maximum EIRP power, that were originally
just there to regulate the inflow of new repeater projects a bit, so
everyone would have a fair chance of running a repeater. if you were
a few km too close, had an antenna a bit high, or similar, it usually
wasn't a problem. but one day an amateur who got refused a license
went to court claiming that others had gotten a license while not being
within the rules, and as a reaction the authority now strictly follows
the rules and refuses every application that does not fully conform to
all the rules. of course, operating on one of the reserved repeater
channels is one of the rules.)

Jim Lux wrote:

Any reason why you're using a split of 600kHz? Why not go to a
non-standard split to make life easier. Pick two frequencies 3 MHz apart
(assuming you can get them coordinated, which is more a political than a
technical issue)

Thanks for the advice and information.

I'm not in the US. 3Mhz split is more than my entire 2m band. :-(

Geoff.


--
Geoffrey S. Mendelson N3OWJ/4X1GM
Making your enemy reliant on software you support is the best revenge.