receiver antenna input protection

[istovit]

My Kenwood R-1000 went hard of hearing recently and I suspect q1,a 3sk74,was taken out on a longwire. what type of diodes can I put at the input so I only do this once. and at what point does their C value affect HF reception?

[Teledog]

A lot of people use 1n914 silicone (or oddball germanium) back to back.
it seems the standard now is the BAV99.
I took them out of my preamp, as there's more loss in VHF/UHF zone.

Tech Note here;
https://www.ti.com/lit/an/slva898/slva898.pdf

G'Luck!

[Solder_Junkie]

Also make sure you have a static drain on your "long wire", as antenna wires of any reasonable length are very prone to picking up static electricity. While it hasn't happened to me, a friend has damaged the input to his transceiver more than once due to static building up on a large wire antenna.

SJ

[A.Z.]

deep sigh

https://www.kk5jy.net/rf-clipper/

make an educated decision

[iMo]

Also the 1N5711 could be a good candidate too. Btw a storm with lightnings in aprox 40km distance from my QTH created 5-6mm long sparks against ground every 5-8 seconds off my 22m long wire antenna.. An unun at the input might be good solution as well (the unun grounded).

[Teledog]

Thought of it at 5:00 AM this morning..
We used to use a plethora of SMD bi-directional TVS suppressors in VOIP boards.
There are a LOT out there.. for voltage, leakage, frequency, etc.
A study in itself..
G' Luck! 

[biastee]

The front end, i.e. 3SK74, could have been damaged by RF overdrive / indirect lightning strike / static - take your pick.

If it is the latter two, then a unun with a ground connection may help.

Some suggested PN diodes, e.g. 1N914, BAV99, Ge, etc., but they will also act a mixer to bring down the IMD performance. A PIN diode limiter would be a better protection for RF overdrive as it is more linear than a PN diode. The package and configuration are important as you want to minimize loss at higher freq. A good reference: http://www.hp.woodshot.com/hprfhelp/5_downld/lit/diodelit/an1050.pdf

As for the suggestion to use a silicon transient voltage suppressor (TVS), most of them don't have low enough capacitance to be inserted into the RF path.

[vk6zgo]

Or your 3SK74 could have just died of old age, FETS are not immune to aging.