Folks,

I have an old eBay Chinese flat pack that I put on the bench to tune for a temporary use repeater. I can notch it down to 90dB just fine. But the insertion loss is horrible. I'm getting around 5dB of loss. I thought something was wrong with the SA/Tracking Generator and plugged it in to the service monitor to test before/after power output and sure enough, 5.4dB insertion loss. SWR is horrible for the actual pass frequency.

I don't think this got dropped (at least not that I know of). I hate to bash a cheap mobile duplexer from China, but I wondering if this has been other's experience of these knock off brand mobile duplexers?

The split is the same as factory...just a few Khz down.

Both sides are within a dB of each other.

-J

开云体育

开云体育

开云体育

Yes, I believe there is.? I think you can select "CSQ", or something similar... but it's been so long since I programmed mine, I seriously can't remember where the selection is.

Thanks - I should have thought of that.

On 9/16/18 11:10 AM, James Adkins adkins.james@... [Repeater-Builder] wrote:

This question is for all the 220 MHz repeater owners on the list.

We have a 25W repeater and would like to add an amplifier as it hears much
better than its transmit coverage. Our exciter output is variable from 1
to 25 Watts. Our antenna is a DB224-JJ.

What type of amplifier are you using? I’m really looking for options other
than Henry and TE Systems but not seeing very many.

I use TE systems, as Henry has failed me before. Henry also takes some time
to actually get them, and power falls off as they warm up.

The TE systems desktop amp with a good fan has worked well for us, but they do
offer the continuous duty option too. TE can operate in a linear mode too.

One of the things I didn't care for with TE systems was they jacked the price
up when I went to order. We'd got the approval of our board for what was
listed on their website plus shipping. When I ordered I was told it would be
about 75 dollars more as "we've not touched the website in 10 years, and
prices have gone up". I'm sure I could have made a thing about it, but it's
just typical old ham mentality.

BTW if you need a circulator or BPF for 220, hit me up.

73's
--
Bryan Fields

727-409-1194 - Voice

High Band MT500.

At 03:34 PM 9/15/18 +0000, you wrote:

Is there a way to program the code plug so that there is no PL tone
transmitted?

You can set both RX and TX to be CSQ, according to both - the help
files - and the test I just did in the program, with an archived codeplug.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

- Adam -

At 9/16/2018 07:39 AM, you wrote:

As you saw, you can improve the input match somewhat by tuning the input
away from the point of lowest noise figure.? At the point of best match, the
NF will be above 1 dB.? For repeater service when the preamp is following
filtering, this is often a better trade-off - I'll take the improved match
over the fraction of a dB of noise figure any day.

If the tradeoff of NF is small (0.2-0.3 dB) I'd agree.? The NF spec on the ARR 440 preamp is 0.5 dB, so if it's meeting spec w/o tuning I wouldn't be so keen on degrading the NF by half a dB just for a better input return loss.? I once had a preamp in service that had an input RL of only ~3 dB & in service it performed identically to an identical model that had much better RL.? No doubt the duplexer got detuned a bit by the poor RL, but in this case it wasn't enough to affect actual on-air performance.? My point is that a preamp with poor RL can still perform well, whereas a preamp with poor NF will not.

Certainly the optimal solution would be good input RL without degrading the NF.? In tests I've conducted on the Mini-Circuits PGA-103 I was able to increase the input RL to > 25 dB over a 25 MHz bandwidth with corresponding NF degradation of 0.15 dB.? IMO this is quite acceptable.

Bob NO6B

I do not know about the RF Amp they use if it could be modified
to work on our 220 Band.

It's quite possible and relatively straight-forward to move a lot of
amplifiers up and down to a new desired band segment. The physical
construction of the amplifier can lend itself to being a modification
candidate. If the form of the amplifier construction, lends itself
to modification(s), then the devices can be evaluated for operation
at the new location (frequency). You might "get away with" operating
the existing transistors a the new location, or you can replace the devices
with better, more optimal (in this example) for 224 MHz operation...
transistors/fets.

I once moved a VHF Micor style PA up to 224 MHz, it was a major pain
in the a$$ and the results were barely 35% of the 152 MHz operation,
mostly because the gain of the transistors, falls off pretty fast. Did the
same thing moving an 800 MHz Micor PA up to 906 MHz, fairly similar
results. But back in the mid 1980's 35 watts on 906 MHz was worth
operating and putting the effort in to doing, because of limited available
alternatives.

We can share that you can buy a VHF TPL, MFJ, RF Concept, 100
Watt VHF/UHF mobile amplifier and rebuild/rework it down or up on to
the 224 MHz band. Again, certain brands and models better lend
themselves to this type of project.

Addressing a few reader concerns... yes, it's a mobile amplifier
with RF sensed "TR" (transmit-receive) switching. The input relay
and TR system can be bypassed easy enough. Others of you have
concerns about the heat buildup. Put the darn thing in a wind tunnel
box and have two fans moving constant air past the heat sink. You
might notice this method is used in some current amplifier products
to reduce the form factor (size) and increase the duty cycle (tuna-fish).

Other more creative types can relocate an amplifier board/circuit on to
a new/larger/faster/bigger/narley/beefier heat sink. Lazier people like
Liberal Democrats can just roughly bolt more heat sink material on to
the existing amplifier, and additionally blow air across the surface(s).

Certain TPL amplifiers are often made up of modules and those modules
lend themselves to relatively easy modification & access. The power
combiner portions of the circuit can be resized for the 224 MHz range,
and there should be no shocking surprises. Part value changes where
required follow fairly well known rules and requirements. Where 60 to
120 Watt level - mobile TPL Amplifiers used/dead/still working can often
be had for a bargain... to the patient and resourceful ham willing to take
on a project.

And many RB Group Members have completed this type of modification
method, numerous times.
They've just not mentioned it before because now the price of a used,
dead, mouse-pee'd on, dusty, muddy, Ebay, flea market, girlfriends
hope-chest found 80 to 100 watt TPL (or similar) amplifier will rise up
past reasonable... but you can always keep your eyes open if you
want to be resourceful and save some money.

cheers,

Milcom Crescend

This question is for all the 220 MHz repeater owners on the list.
We have a 25W repeater and would like to add an amplifier.

Do we actually have to own a 224 MHz repeater to answer these
questions?

I’m really looking for options other than Henry and TE Systems
but not seeing very many.

There is not yet a practical reply in the queue because you
should provide an answer to the following question(s).

Do you want to buy a complete and ready to operate ("plug
and play") amplifier, or would you be willing to modify or repair
an existing product? Even more involved, would you consider
actually building an amplifier? .... from scratch? from parts?
from a parts donor amplifier? ... from your neighbors discarded
microwave oven?

As with that famous pine tree... many parts are edible. We might
like a better idea of what you're willing to chew on.

cheers,
Grape Nuts

开云体育

开云体育

At 9/15/2018 05:31 PM, you wrote:

Matt W6KGB makes darned GOOD preamps - the performance is equal or
better than the no-longer-available Anglelinear in every way (and
a helluva lot better than ARR, in fact the last time I was in
Matt's shop he was repairing a few dead ARRs for a customer in
the midwest).

I 2nd the above, though with all the duplicated messages on Yahoogroups lately this may turn into a 3rd, 4th, 5th,...

Bob NO6B