Good morning,

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.

James Adkins, KB0NHX
Repeater Trustee - Nixa Amateur Radio Club, Inc (K0NXA)
www.nixahams.net

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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

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

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

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I have modified a couple of "LM" (Linear Modulation) brand ACSB Repeater PAs for FM Use.? It is quite easy.? There is a switching transistor that gets removed and replaced with a jumper - that's it.? If I recall they are about 500mw in for 100W Out.? I did a bench test and made a chart that I put on the PA with the various input/output levels.? The other benefit is if you get the entire repeater you can remove or modify the Exciter and Receiver modules, replacing them with an FM Receiver and Exciter and have everything in the same chassis.? The power supply uses XLR connectors for 13.8VDC supply to the various modules - so just plug and play any 13.8V receiver/exciter.? I have had one of these on the air for close to 10 years with a pair of Alinco DR-235s and an attenuator on the transmit radio.? It works very well - so well that I found a spare and have kept it around.