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FAQ's

Q: Which preamplifier type should I use, GaAsFET, DGFET or bipolar?

A:
The type of amplifier you choose depends to some extent on your application. However, the GaAsFET type does offer the best noise figure (N.F.) and therefore the best sensitivity of the various types. It also has the most gain and best immunity to overload. Looking at the 1 dB compression (1 dB comp.) characteristics, the GaAsFET is 12 dB better than the DGFET type and 32 dB better than the low noise bipolar.

Q: What is 1 dB comp?

A:
1 dB compression is a measure of strong signal handling capability of an amplifier. 1 dB compression is the power output, in dBm, at which the preamplifier goes into gain compression. The output no longer follows the input linearly once the preamplifier is in gain compression. Although the preamplifier is not normally run at these levels it serves as a good method for comparing one amplifier to another. DBm is db referenced to 1 milliwatt. 0 dBm = 1 milliwatt, +10 dBm = 10 milliwatts and so on.

Q: Can the preamplifiers be detuned for less gain?

A:
Detuning the preamplifier to reduce the gain is not a good idea as it will adversely affect the noise figure and overload characteristics of the preamplifier. In the rare instances that a preamplifier has too much gain for a particular receiver system a resistive attenuator placed between the output of the preamplifier and the input to the receiver is the proper course of action. The value of attenuation reduces the preamplifier gain by a like amount. For example a 24 dB gain preamplifier followed by a 6 dB attenuator will yield a combined gain of 18 dB.

Q: My repeater has some desence. Will a preamplifier help that situation?

A:
No. Adding a preamplifier under these conditions will only make the situation worse. Desence is caused by the lack of isolation in the duplexer allowing sufficient transmitter energy into the receiver to compromise the receivers ability to detect weak signals. The duplexer must be retuned or more cavities must be added to improve isolation before adding the preamplifier. A repeater that does not suffer from desence will not normally have a problem when a preamplifier is added.

Q: What other connector types are available?

A:
P, SP, DCINJ and PD series come standard with BNC type connectors. Type F and RCA phono are available at no additional cost. Type N, SMA, TNC and mini UHF are available for an additional $10.00. Standard UHF is not available. MSP series come standard with N connectors. UHF is available at no additional cost. All connectors used are female.

Q: Can I run more than 25 watts through an SP series preamplifier?

A:
We recommend no more than 25 watts be run through the SP series preamplifiers in the interest of long relay life. 30 watts maybe, but beyond that you're on your own.

Q: If the preamplifier is turned off can I run more than 25 watts through it?

A:
No. Whether the preamplifier is turned on or off, the transmitter power must still pass through the relays. Therefore, the same situation applies to both the on and off conditions.

Q: How do I connect to the vdc connector on the P, SP, and DCINJ units?

A:
That connection device is called a feedthrough capacitor and provides an rf shielded means to get power to the preamplifier. Simply solder directly to the center pin of the feedthrough capacitor.

Q: Can P and SP series be tower mounted as is?

A:
No. P and SP series preamplifiers are not waterproof. They will easily take the environmental temperature extremes, however, they should be placed in waterproof enclosures such as many NEMA approved enclosures.

Q: What temperature extremes will the preamplifiers take?

A:
Preamplifiers are specified for operation from at least -25° to +60° C. We have numerous preamplifiers operating for years on end in the Antarctic and various equatorial locations.

Q: Do you sell through distributors?

A:
It has been our policy to sell factory direct only. In this manner, we can provide the ultimate in customer service for stock or special frequency/connector preamplifiers. Most units, even special frequency/connector units are shipped the same or next day.

Q: Do you offer quantity discounts?

A:
Yes. Quantity discounts start at 5 pieces of the same part number. Contact factory for pricing.

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